fix checkout again

.dockerignore

@@ -0,0 +1,68 @@
+# .dockerignore for go-cart-actor
+#
+# Goal: Keep Docker build context lean & reproducible.
+# Adjust as project structure evolves.
+
+# Version control & CI metadata
+.git
+.git/
+.gitignore
+.github
+
+# Local tooling / editors
+.vscode
+.idea
+*.iml
+
+# Build artifacts / outputs
+bin/
+build/
+dist/
+out/
+coverage/
+*.coverprofile
+
+# Temporary files
+*.tmp
+*.log
+tmp/
+.tmp/
+
+# Dependency/vendor caches (not used; rely on go modules download)
+vendor/
+
+# Examples / scripts (adjust if you actually need them in build context)
+examples/
+scripts/
+
+# Docs (retain README.md explicitly)
+docs/
+CHANGELOG*
+**/*.md
+!README.md
+
+# Tests (not needed for production build)
+**/*_test.go
+
+# Node / frontend artifacts (if any future addition)
+node_modules/
+
+# Docker / container metadata not needed inside image
+Dockerfile
+
+# Editor swap/backup files
+*~
+*.swp
+
+# Go race / profiling outputs
+*.pprof
+
+# Security / secret placeholders (ensure real secrets never copied)
+*.secret
+*.key
+*.pem
+
+# Keep proto and generated code (do NOT ignore proto/)
+!proto/
+
+# End of file

.gitea/workflows/build.yaml

@@ -1,30 +1,77 @@
 name: Build and Publish
-run-name: ${{ gitea.actor }} is building 🚀
+run-name: ${{ gitea.actor }} build 🚀
 on: [push]
 
 jobs:
-  BuildAndDeployAmd64:
+    Metadata:
-    runs-on: amd64
+        runs-on: arm64
-    steps:
+        outputs:
-      - name: Check out repository code
+            version: ${{ steps.meta.outputs.version }}
-        uses: actions/checkout@v4
+            git_commit: ${{ steps.meta.outputs.git_commit }}
-      - name: Build docker image
+            build_date: ${{ steps.meta.outputs.build_date }}
-        run: docker build --progress=plain -t registry.knatofs.se/go-cart-actor-amd64:latest .
+        steps:
-      - name: Push to registry
+            - name: Checkout
-        run: docker push registry.knatofs.se/go-cart-actor-amd64:latest
+              uses: actions/checkout@v4
-      - name: Deploy to Kubernetes
+            - id: meta
-        run: kubectl apply -f deployment/deployment.yaml -n cart
+              name: Derive build metadata
-      - name: Rollout amd64 deployment
+              run: |
-        run: kubectl rollout restart deployment/cart-actor-x86 -n cart
+                  GIT_COMMIT=$(git rev-parse HEAD)
-  
+                  if git describe --tags --exact-match >/dev/null 2>&1; then
-  BuildAndDeploy:
+                    VERSION=$(git describe --tags --exact-match)
-    runs-on: arm64
+                  else
-    steps:
+                    VERSION=$(git rev-parse --short=12 HEAD)
-      - name: Check out repository code
+                  fi
-        uses: actions/checkout@v4
+                  BUILD_DATE=$(date -u +"%Y-%m-%dT%H:%M:%SZ")
-      - name: Build docker image
+                  echo "git_commit=$GIT_COMMIT" >> $GITHUB_OUTPUT
-        run: docker build --progress=plain -t registry.knatofs.se/go-cart-actor .
+                  echo "version=$VERSION" >> $GITHUB_OUTPUT
-      - name: Push to registry
+                  echo "build_date=$BUILD_DATE" >> $GITHUB_OUTPUT
-        run: docker push registry.knatofs.se/go-cart-actor
+
-      - name: Rollout arm64 deployment
+    BuildAndDeployAmd64:
-        run: kubectl rollout restart deployment/cart-actor-arm64 -n cart
+        needs: Metadata
+        runs-on: amd64
+        steps:
+            - uses: actions/checkout@v4
+            - name: Build amd64 image
+              run: |
+                  docker build \
+                    --build-arg VERSION=${{ needs.Metadata.outputs.version }} \
+                    --build-arg GIT_COMMIT=${{ needs.Metadata.outputs.git_commit }} \
+                    --build-arg BUILD_DATE=${{ needs.Metadata.outputs.build_date }} \
+                    --progress=plain \
+                    -t registry.knatofs.se/go-cart-actor-amd64:latest \
+                    -t registry.knatofs.se/go-cart-actor-amd64:${{ needs.Metadata.outputs.version }} \
+                    .
+            - name: Push amd64 images
+              run: |
+                  docker push registry.knatofs.se/go-cart-actor-amd64:latest
+                  docker push registry.knatofs.se/go-cart-actor-amd64:${{ needs.Metadata.outputs.version }}
+            - name: Apply deployment manifests
+              run: kubectl apply -f deployment/deployment.yaml -n cart
+            - name: Rollout amd64 deployment (pin to version)
+              run: |
+                  kubectl set image deployment/cart-actor-x86 -n cart cart-actor-amd64=registry.knatofs.se/go-cart-actor-amd64:${{ needs.Metadata.outputs.version }}
+                  kubectl rollout status deployment/cart-actor-x86 -n cart
+
+    BuildAndDeployArm64:
+        needs: Metadata
+        runs-on: arm64
+        steps:
+            - uses: actions/checkout@v4
+            - name: Build arm64 image
+              run: |
+                  docker build \
+                    --build-arg VERSION=${{ needs.Metadata.outputs.version }} \
+                    --build-arg GIT_COMMIT=${{ needs.Metadata.outputs.git_commit }} \
+                    --build-arg BUILD_DATE=${{ needs.Metadata.outputs.build_date }} \
+                    --progress=plain \
+                    -t registry.knatofs.se/go-cart-actor:latest \
+                    -t registry.knatofs.se/go-cart-actor:${{ needs.Metadata.outputs.version }} \
+                    .
+            - name: Push arm64 images
+              run: |
+                  docker push registry.knatofs.se/go-cart-actor:latest
+                  docker push registry.knatofs.se/go-cart-actor:${{ needs.Metadata.outputs.version }}
+            - name: Rollout arm64 deployment (pin to version)
+              run: |
+                  kubectl set image deployment/cart-actor-arm64 -n cart cart-actor-arm64=registry.knatofs.se/go-cart-actor:${{ needs.Metadata.outputs.version }}
+                  kubectl rollout status deployment/cart-actor-arm64 -n cart

Dockerfile

@@ -1,17 +1,75 @@
-# syntax=docker/dockerfile:1
+# syntax=docker/dockerfile:1.7
+#
+# Multi-stage build:
+#  1. Build static binary with pinned Go version (matching go.mod).
+#  2. Copy into distroless static nonroot runtime image.
+#
+# Build args (optional):
+#   VERSION      - semantic/app version (default: dev)
+#   GIT_COMMIT   - git SHA (default: unknown)
+#   BUILD_DATE   - RFC3339 build timestamp
+#
+# Example build:
+#   docker build \
+#     --build-arg VERSION=$(git describe --tags --always) \
+#     --build-arg GIT_COMMIT=$(git rev-parse HEAD) \
+#     --build-arg BUILD_DATE=$(date -u +%Y-%m-%dT%H:%M:%SZ) \
+#     -t go-cart-actor:dev .
+#
+# If you add subpackages or directories, no Dockerfile change needed (COPY . .).
+# Ensure a .dockerignore exists to keep context lean.
 
-FROM golang:alpine AS build-stage
+############################
-WORKDIR /app
+# Build Stage
+############################
+FROM golang:1.25-alpine AS build
+WORKDIR /src
+
+# Build metadata (can be overridden at build time)
+ARG VERSION=dev
+ARG GIT_COMMIT=unknown
+ARG BUILD_DATE=unknown
+
+# Ensure reproducible static build
+# Multi-arch build args (TARGETOS/TARGETARCH provided automatically by buildx)
+ARG TARGETOS
+ARG TARGETARCH
+ENV CGO_ENABLED=0 GOOS=${TARGETOS:-linux} GOARCH=${TARGETARCH}
+
+# Dependency caching
 COPY go.mod go.sum ./
-RUN go mod download
+RUN --mount=type=cache,target=/go/pkg/mod \
+    go mod download
 
-COPY proto ./proto
+# Copy full source (relay on .dockerignore to prune)
-COPY *.go ./
+COPY . .
 
-RUN CGO_ENABLED=0 GOOS=linux go build -o /go-cart-actor
+# (Optional) If you do NOT check in generated protobuf code, uncomment generation:
+# RUN go install google.golang.org/protobuf/cmd/protoc-gen-go@latest && \
+#     go install google.golang.org/grpc/cmd/protoc-gen-go-grpc@latest && \
+#     protoc --go_out=. --go_opt=paths=source_relative \
+#            --go-grpc_out=. --go-grpc_opt=paths=source_relative \
+#            proto/*.proto
 
-FROM gcr.io/distroless/base-debian11
+# Build with minimal binary size and embedded metadata
+RUN --mount=type=cache,target=/go/build-cache \
+    go build -trimpath -ldflags="-s -w \
+      -X main.Version=${VERSION} \
+      -X main.GitCommit=${GIT_COMMIT} \
+      -X main.BuildDate=${BUILD_DATE}" \
+      -o /out/go-cart-actor .
+
+############################
+# Runtime Stage
+############################
+# Using distroless static (nonroot) for minimal surface area.
+FROM gcr.io/distroless/static-debian12:nonroot AS runtime
 WORKDIR /
 
-COPY --from=build-stage /go-cart-actor /go-cart-actor
+COPY --from=build /out/go-cart-actor /go-cart-actor
-ENTRYPOINT ["/go-cart-actor"]
+
+# Document (not expose forcibly) typical ports: 8080 (HTTP), 1337 (gRPC)
+EXPOSE 8080 1337
+
+USER nonroot:nonroot
+ENTRYPOINT ["/go-cart-actor"]

GRPC-MIGRATION-PLAN.md

@@ -1,396 +0,0 @@
-# gRPC Migration Plan
-
-File: GRPC-MIGRATION-PLAN.md  
-Author: (Generated plan)  
-Status: Draft for review  
-Target Release: Next major version (breaking change – no mixed compatibility)
-
----
-
-## 1. Overview
-
-This document describes the full migration of the current custom TCP frame-based protocol (both the cart mutation/state channel on port `1337` and the control plane on port `1338`) to gRPC. We will remove all legacy packet framing (`FrameWithPayload`, `RemoteGrain`, `GenericListener` handlers for these two ports) and replace them with two gRPC services:
-
-1. Cart Actor Service (mutations + state retrieval)
-2. Control Plane Service (cluster membership, negotiation, ownership change, lifecycle)
-
-We intentionally keep:
-- Internal `CartGrain` logic, message storage format, disk persistence, and JSON cart serialization.
-- Existing message type numeric mapping for backward compatibility with persisted event logs.
-- HTTP/REST API layer unchanged (it still consumes JSON state from the local/remote grain pipeline).
-
-We do NOT implement mixed-version compatibility; migration occurs atomically (cluster restart with new image).
-
----
-
-## 2. Goals
-
-- Remove custom binary frame protocol & simplify maintenance.
-- Provide clearer, strongly defined interfaces via `.proto` schemas.
-- Improve observability via gRPC interceptors (metrics & tracing hooks).
-- Reduce per-call overhead compared with the current manual connection pooling + handwritten framing (HTTP/2 multiplexing + connection reuse).
-- Prepare groundwork for future enhancements (streaming, typed state, event streaming) without rewriting again.
-
----
-
-## 3. Non-Goals (Phase 1)
-
-- Converting the cart state payload from JSON to a strongly typed proto.
-- Introducing authentication / mTLS (may be added later).
-- Changing persistence or replay format.
-- Changing the HTTP API contract.
-- Implementing streaming watchers or push updates.
-
----
-
-## 4. Architecture After Migration
-
-Ports:  
-- `:1337` → gRPC CartActor service.  
-- `:1338` → gRPC ControlPlane service.
-
-Each node:
-- Runs one gRPC server with both services (can use a single listener bound to two services or keep two separate listeners; we will keep two ports initially to minimize operational surprise, but they could be merged later).
-- Maintains a connection pool of `*grpc.ClientConn` objects keyed by remote hostname (one per remote host, reused for both services).
-
-Call Flow (Mutation):
-1. HTTP request hits `PoolServer`.
-2. `SyncedPool.getGrain(cartId)`:
-   - Local: direct invocation.
-   - Remote: uses `RemoteGrainGRPC` (new) which invokes `CartActor.Mutate`.
-3. Response JSON returned unchanged.
-
-Control Plane Flow:
-- Discovery (K8s watch) still triggers `AddRemote(host)`.
-- Instead of custom `Ping`, `Negotiate`, etc. via frames, call gRPC methods on `ControlPlane` service.
-- Ownership changes use `ConfirmOwner` RPC.
-
----
-
-## 5. Proto Design
-
-### 5.1 Cart Actor Proto (Envelope Pattern)
-
-We keep an envelope with `bytes payload` holding the serialized underlying cart mutation proto (existing types in `messages.proto`). This minimizes churn.
-
-Indented code block (proto sketch):
-
-    syntax = "proto3";
-    package cart;
-    option go_package = "git.tornberg.me/go-cart-actor/proto;proto";
-
-    enum MutationType {
-      MUTATION_TYPE_UNSPECIFIED = 0;
-      MUTATION_ADD_REQUEST = 1;
-      MUTATION_ADD_ITEM = 2;
-      MUTATION_REMOVE_ITEM = 4;
-      MUTATION_REMOVE_DELIVERY = 5;
-      MUTATION_CHANGE_QUANTITY = 6;
-      MUTATION_SET_DELIVERY = 7;
-      MUTATION_SET_PICKUP_POINT = 8;
-      MUTATION_CREATE_CHECKOUT_ORDER = 9;
-      MUTATION_SET_CART_ITEMS = 10;
-      MUTATION_ORDER_COMPLETED = 11;
-    }
-
-    message MutationRequest {
-      string cart_id = 1;
-      MutationType type = 2;
-      bytes payload = 3;          // Serialized specific mutation proto
-      int64 client_timestamp = 4; // Optional; server fills if zero
-    }
-
-    message MutationReply {
-      int32 status_code = 1;
-      bytes payload = 2; // JSON cart state or error string
-    }
-
-    message StateRequest {
-      string cart_id = 1;
-    }
-
-    message StateReply {
-      int32 status_code = 1;
-      bytes payload = 2; // JSON cart state
-    }
-
-    service CartActor {
-      rpc Mutate(MutationRequest) returns (MutationReply);
-      rpc GetState(StateRequest) returns (StateReply);
-    }
-
-### 5.2 Control Plane Proto
-
-    syntax = "proto3";
-    package control;
-    option go_package = "git.tornberg.me/go-cart-actor/proto;proto";
-
-    message Empty {}
-
-    message PingReply {
-      string host = 1;
-      int64 unix_time = 2;
-    }
-
-    message NegotiateRequest {
-      repeated string known_hosts = 1;
-    }
-    message NegotiateReply {
-      repeated string hosts = 1; // Healthy hosts returned
-    }
-
-    message CartIdsReply {
-      repeated string cart_ids = 1;
-    }
-
-    message OwnerChangeRequest {
-      string cart_id = 1;
-      string new_host = 2;
-    }
-    message OwnerChangeAck {
-      bool accepted = 1;
-      string message = 2;
-    }
-
-    message ClosingNotice {
-      string host = 1;
-    }
-
-    service ControlPlane {
-      rpc Ping(Empty) returns (PingReply);
-      rpc Negotiate(NegotiateRequest) returns (NegotiateReply);
-      rpc GetCartIds(Empty) returns (CartIdsReply);
-      rpc ConfirmOwner(OwnerChangeRequest) returns (OwnerChangeAck);
-      rpc Closing(ClosingNotice) returns (OwnerChangeAck);
-    }
-
----
-
-## 6. Message Type Mapping
-
-| Legacy Constant | Numeric | New Enum Value              |
-|-----------------|---------|-----------------------------|
-| AddRequestType  | 1       | MUTATION_ADD_REQUEST        |
-| AddItemType     | 2       | MUTATION_ADD_ITEM           |
-| RemoveItemType  | 4       | MUTATION_REMOVE_ITEM        |
-| RemoveDeliveryType | 5    | MUTATION_REMOVE_DELIVERY    |
-| ChangeQuantityType | 6    | MUTATION_CHANGE_QUANTITY    |
-| SetDeliveryType | 7       | MUTATION_SET_DELIVERY       |
-| SetPickupPointType | 8    | MUTATION_SET_PICKUP_POINT   |
-| CreateCheckoutOrderType | 9 | MUTATION_CREATE_CHECKOUT_ORDER |
-| SetCartItemsType | 10     | MUTATION_SET_CART_ITEMS     |
-| OrderCompletedType | 11   | MUTATION_ORDER_COMPLETED    |
-
-Persisted events keep original numeric codes; reconstruction simply casts to `MutationType`.
-
----
-
-## 7. Components To Remove / Replace
-
-Remove (after migration complete):
-- `remote-grain.go`
-- `rpc-server.go`
-- Any packet/frame-specific types solely used by the above (search: `FrameWithPayload`, `RemoteHandleMutation`, `RemoteGetState` where not reused by disk or internal logic).
-- The constants representing network frame types in `synced-pool.go` (RemoteNegotiate, AckChange, etc.) replaced by gRPC calls.
-- netpool usage for remote cart channel (control plane also no longer needs `Connection` abstraction).
-
-Retain (until reworked or optionally cleaned later):
-- `message.go` (for persistence)
-- `message-handler.go`
-- `cart-grain.go`
-- `messages.proto` (underlying mutation messages)
-- HTTP API server and REST handlers.
-
----
-
-## 8. New / Modified Components
-
-New files (planned):
-- `proto/cart_actor.proto`
-- `proto/control_plane.proto`
-- `grpc/cart_actor_server.go` (server impl)
-- `grpc/cart_actor_client.go` (client adapter implementing `Grain`)
-- `grpc/control_plane_server.go`
-- `grpc/control_plane_client.go`
-- `grpc/interceptors.go` (metrics, logging, optional tracing hooks)
-- `remote_grain_grpc.go` (adapter bridging existing interfaces)
-- `control_plane_adapter.go` (replaces frame handlers in `SyncedPool`)
-
-Modified:
-- `synced-pool.go` (remote host management now uses gRPC clients; negotiation logic updated)
-- `main.go` (initialize both gRPC services on startup)
-- `go.mod` (add `google.golang.org/grpc`)
-
----
-
-## 9. Step-by-Step Migration Plan
-
-1. Add proto files and generate Go code (`protoc --go_out --go-grpc_out`).
-2. Implement `CartActorServer`:
-   - Translate `MutationRequest` to `Message`.
-   - Use existing handler registry for payload encode/decode.
-   - Return JSON cart state.
-3. Implement `CartActorClient` wrapper (`RemoteGrainGRPC`) implementing:
-   - `HandleMessage`: Build envelope, call `Mutate`.
-   - `GetCurrentState`: Call `GetState`.
-4. Implement `ControlPlaneServer` with methods:
-   - `Ping`: returns host + time.
-   - `Negotiate`: merge host lists; emulate old logic.
-   - `GetCartIds`: iterate local grains.
-   - `ConfirmOwner`: replicate quorum flow (accept always; error path for future).
-   - `Closing`: schedule remote removal.
-5. Implement `ControlPlaneClient` used inside `SyncedPool.AddRemote`.
-6. Refactor `SyncedPool`:
-   - Replace frame handlers registration with gRPC client calls.
-   - Replace `Server.AddHandler(...)` start-up with launching gRPC server.
-   - Implement periodic health checks using `Ping`.
-7. Remove old connection constructs for 1337/1338.
-8. Metrics:
-   - Add unary interceptor capturing duration and status.
-   - Replace packet counters with `cart_grpc_mutate_calls_total`, `cart_grpc_control_calls_total`, histograms for latency.
-9. Update `main.go` to start:
-   - gRPC server(s).
-   - HTTP server as before.
-10. Delete legacy files & update README build instructions.
-11. Load testing & profiling on Raspberry Pi hardware (or ARM emulation).
-12. Final cleanup & dead code removal (search for now-unused constants & structs).
-13. Tag release.
-
----
-
-## 10. Performance Considerations (Raspberry Pi Focus)
-
-- Single `*grpc.ClientConn` per remote host (HTTP/2 multiplexing) to reduce file descriptor and handshake overhead.
-- Use small keepalive pings (optional) only if connections drop; default may suffice.
-- Avoid reflection / dynamic dispatch in hot path: pre-build a mapping from `MutationType` to handler function.
-- Reuse byte buffers:
-  - Implement a `sync.Pool` for mutation serialization to reduce GC pressure.
-- Enforce per-RPC deadlines (e.g. 300–400ms) to avoid pile-ups.
-- Backpressure:
-  - Before dispatch: if local grain pool at capacity and target grain is remote, abort early with 503 to caller (optional).
-- Disable gRPC compression for small payloads (mutation messages are small). Condition compression if payload > threshold (e.g. 8KB).
-- Compile with `-ldflags="-s -w"` in production to reduce binary size (optional).
-- Enable `GOMAXPROCS` tuned to CPU cores; Pi often benefits from leaving default but monitor.
-- Use histograms with limited buckets to reduce Prometheus cardinality.
-
----
-
-## 11. Testing Strategy
-
-Unit:
-- Message type mapping tests (legacy -> enum).
-- Envelope roundtrip: Original proto -> payload -> gRPC -> server decode -> internal Message.
-
-Integration:
-- Two-node cluster simulation:
-  - Mutate cart on Node A, ownership moves, verify remote access from Node B.
-  - Quorum failure simulation (temporarily reject `ConfirmOwner`).
-- Control plane negotiation: start nodes in staggered order, assert final membership.
-
-Load/Perf:
-- Benchmark local mutation vs remote mutation latency.
-- High concurrency test (N goroutines each performing X mutations).
-- Memory profiling (ensure no large buffer retention).
-
-Failure Injection:
-- Kill a node mid-mutation; client call should timeout and not corrupt local state.
-- Simulated network partition: drop `Ping` replies; ensure host removal path triggers.
-
----
-
-## 12. Rollback Strategy
-
-Because no mixed-version compatibility is provided, rollback = redeploy previous version containing legacy protocol:
-1. Stop all new-version pods.
-2. Deploy old version cluster-wide.
-3. No data migration needed (event persistence unaffected).
-
-Note: Avoid partial upgrades; perform full rolling restart quickly to prevent split-brain (new nodes won’t talk to old nodes).
-
----
-
-## 13. Risks & Mitigations
-
-| Risk | Description | Mitigation |
-|------|-------------|------------|
-| Full-cluster restart required | No mixed compatibility | Schedule maintenance window |
-| gRPC adds CPU overhead | Envelope + marshaling cost | Buffer reuse, keep small messages uncompressed |
-| Ownership race | Timing differences after refactor | Add explicit logs + tests around `RequestOwnership` path |
-| Hidden dependency on frame-level status codes | Some code may assume `FrameWithPayload` fields | Wrap gRPC responses into minimal compatibility structs until fully removed |
-| Memory growth | Connection reuse & pooled buffers not implemented initially | Add `sync.Pool` & track memory via pprof early |
-
----
-
-## 14. Logging & Observability
-
-- Structured log entries for:
-  - Ownership changes
-  - Negotiation rounds
-  - Remote spawn events
-  - Mutation failures (with cart id, mutation type)
-- Metrics:
-  - `cart_grpc_mutate_duration_seconds` (histogram)
-  - `cart_grpc_mutate_errors_total`
-  - `cart_grpc_control_duration_seconds`
-  - `cart_remote_hosts` (gauge)
-  - Retain existing grain counts.
-- Optional future: OpenTelemetry tracing (span per remote mutation).
-
----
-
-## 15. Future Enhancements (Post-Migration)
-
-- Replace JSON state with `CartState` proto and provide streaming watch API.
-- mTLS between nodes (certificate rotation via K8s Secret or SPIRE).
-- Distributed tracing integration.
-- Ownership leasing with TTL and optimistic renewal.
-- Delta replication or CRDT-based conflict resolution for experimentation.
-
----
-
-## 16. Task Breakdown & Estimates
-
-| Task | Estimate |
-|------|----------|
-| Proto definitions & generation | 0.5d |
-| CartActor server/client | 1.0d |
-| ControlPlane server/client | 1.0d |
-| SyncedPool refactor | 1.0d |
-| Metrics & interceptors | 0.5d |
-| Remove legacy code & cleanup | 0.5d |
-| Tests (unit + integration) | 1.5d |
-| Benchmark & tuning | 0.5–1.0d |
-| Total | ~6–7d |
-
----
-
-## 17. Open Questions (Confirm Before Implementation)
-
-1. Combine both services on a single port (simplify ops) or keep dual-port first? (Default here: keep dual, but easy to merge.)
-2. Minimum Go version remains 1.24.x—acceptable to add `google.golang.org/grpc` latest?
-3. Accept adding `sync.Pool` micro-optimizations in first pass or postpone?
-
----
-
-## 18. Acceptance Criteria
-
-- All previous integration tests (adjusted to gRPC) pass.
-- Cart operations (add, remove, delivery, checkout) function across at least a 2‑node cluster.
-- Control plane negotiation forms consistent host list.
-- Latency for a remote mutation does not degrade beyond an acceptable threshold (define baseline before merge).
-- Legacy networking code fully removed.
-
----
-
-## 19. Next Steps (If Approved)
-
-1. Implement proto files and commit.
-2. Scaffold server & client code.
-3. Refactor `SyncedPool` and `main.go`.
-4. Add metrics and tests.
-5. Run benchmark on target Pi hardware.
-6. Review & merge.
-
----
-
-End of Plan.

Makefile

@@ -0,0 +1,132 @@
+# ------------------------------------------------------------------------------
+# Makefile for go-cart-actor
+#
+# Key targets:
+#   make protogen      - Generate protobuf + gRPC code into proto/
+#   make clean_proto   - Remove generated proto *.pb.go files
+#   make verify_proto  - Ensure no stray root-level *.pb.go files exist
+#   make build         - Build the project
+#   make test          - Run tests (verbose)
+#   make tidy          - Run go mod tidy
+#   make regen         - Clean proto, regenerate, tidy, verify, build
+#   make help          - Show this help
+#
+# Conventions:
+#   - All .proto files live in $(PROTO_DIR)
+#   - Generated Go code is emitted under $(PROTO_DIR) via go_package mapping
+#   - go_package is set to: git.tornberg.me/go-cart-actor/proto;messages
+# ------------------------------------------------------------------------------
+
+MODULE_PATH := git.tornberg.me/go-cart-actor
+PROTO_DIR   := proto
+PROTOS      := $(PROTO_DIR)/messages.proto $(PROTO_DIR)/cart_actor.proto $(PROTO_DIR)/control_plane.proto
+
+# Allow override: make PROTOC=/path/to/protoc
+PROTOC ?= protoc
+
+# Tools (auto-detect; can override)
+PROTOC_GEN_GO        ?= $(shell command -v protoc-gen-go 2>/dev/null)
+PROTOC_GEN_GO_GRPC   ?= $(shell command -v protoc-gen-go-grpc 2>/dev/null)
+
+GO        ?= go
+
+# Colors (optional)
+GREEN  := \033[32m
+RED    := \033[31m
+YELLOW := \033[33m
+RESET  := \033[0m
+
+# ------------------------------------------------------------------------------
+
+.PHONY: protogen clean_proto verify_proto tidy build test regen help check_tools
+
+help:
+	@echo "Available targets:"
+	@echo "  protogen      Generate protobuf & gRPC code"
+	@echo "  clean_proto   Remove generated *.pb.go files in $(PROTO_DIR)"
+	@echo "  verify_proto  Ensure no root-level *.pb.go files (old layout)"
+
+	@echo "  tidy          Run go mod tidy"
+	@echo "  build         Build the module"
+	@echo "  test          Run tests (verbose)"
+	@echo "  regen         Clean proto, regenerate, tidy, verify, and build"
+	@echo "  check_tools   Verify protoc + plugins are installed"
+
+check_tools:
+	@if [ -z "$(PROTOC_GEN_GO)" ] || [ -z "$(PROTOC_GEN_GO_GRPC)" ]; then \
+		echo "$(RED)Missing protoc-gen-go or protoc-gen-go-grpc in PATH.$(RESET)"; \
+		echo "Install with:"; \
+		echo "  go install google.golang.org/protobuf/cmd/protoc-gen-go@latest"; \
+		echo "  go install google.golang.org/grpc/cmd/protoc-gen-go-grpc@latest"; \
+		exit 1; \
+	fi
+	@if ! command -v "$(PROTOC)" >/dev/null 2>&1; then \
+		echo "$(RED)protoc not found. Install protoc (e.g. via package manager)$(RESET)"; \
+		exit 1; \
+	fi
+	@echo "$(GREEN)All required tools detected.$(RESET)"
+
+protogen: check_tools
+	@echo "$(YELLOW)Generating protobuf code (outputs -> ./proto)...$(RESET)"
+	$(PROTOC) -I $(PROTO_DIR) \
+	  --go_out=./proto --go_opt=paths=source_relative \
+	  --go-grpc_out=./proto --go-grpc_opt=paths=source_relative \
+	  $(PROTOS)
+	@echo "$(GREEN)Protobuf generation complete.$(RESET)"
+
+clean_proto:
+	@echo "$(YELLOW)Removing generated protobuf files...$(RESET)"
+	@rm -f $(PROTO_DIR)/*_grpc.pb.go $(PROTO_DIR)/*.pb.go
+	@rm -f *.pb.go
+	@rm -rf git.tornberg.me
+	@echo "$(GREEN)Clean complete.$(RESET)"
+
+verify_proto:
+	@echo "$(YELLOW)Verifying proto layout...$(RESET)"
+	@if ls *.pb.go >/dev/null 2>&1; then \
+		echo "$(RED)ERROR: Found root-level generated *.pb.go files (should be only under $(PROTO_DIR)/).$(RESET)"; \
+		ls -1 *.pb.go; \
+		exit 1; \
+	fi
+	@echo "$(GREEN)Proto layout OK (no root-level *.pb.go files).$(RESET)"
+
+
+
+
+
+
+
+
+
+
+
+
+
+tidy:
+	@echo "$(YELLOW)Running go mod tidy...$(RESET)"
+	$(GO) mod tidy
+	@echo "$(GREEN)tidy complete.$(RESET)"
+
+build:
+	@echo "$(YELLOW)Building...$(RESET)"
+	$(GO) build ./...
+	@echo "$(GREEN)Build success.$(RESET)"
+
+test:
+	@echo "$(YELLOW)Running tests...$(RESET)"
+	$(GO) test -v ./...
+	@echo "$(GREEN)Tests completed.$(RESET)"
+
+regen: clean_proto protogen tidy verify_proto build
+	@echo "$(GREEN)Full regenerate cycle complete.$(RESET)"
+
+# Utility: show proto sources and generated outputs
+print_proto:
+	@echo "Proto sources:"
+	@ls -1 $(PROTOS)
+	@echo ""
+	@echo "Generated files (if any):"
+	@ls -1 $(PROTO_DIR)/*pb.go 2>/dev/null || echo "(none)"
+
+# Prevent make from treating these as file targets if similarly named files appear.
+.SILENT: help check_tools protogen clean_proto verify_proto tidy build test regen print_proto

README.md

@@ -1,5 +1,36 @@
 # Go Cart Actor
 
+## Migration Notes (Ring-based Ownership Transition)
+
+This release removes the legacy ConfirmOwner ownership negotiation RPC in favor of deterministic ownership via the consistent hashing ring.
+
+Summary of changes:
+- ConfirmOwner RPC removed from the ControlPlane service.
+- OwnerChangeRequest message removed (was only used by ConfirmOwner).
+- OwnerChangeAck retained solely as the response type for the Closing RPC.
+- SyncedPool now relies exclusively on the ring for ownership (no quorum negotiation).
+- Remote proxy creation includes a bounded readiness retry to reduce first-call failures.
+- New Prometheus ring metrics: 
+  - cart_ring_epoch
+  - cart_ring_hosts
+  - cart_ring_vnodes
+  - cart_ring_host_share{host}
+  - cart_ring_lookup_local_total
+  - cart_ring_lookup_remote_total
+
+Action required for consumers:
+1. Regenerate protobuf code after pulling (requires protoc-gen-go and protoc-gen-go-grpc installed).
+2. Remove any client code or automation invoking ConfirmOwner (calls will now return UNIMPLEMENTED if using stale generated stubs).
+3. Update monitoring/alerts that referenced ConfirmOwner or ownership quorum failures—use ring metrics instead.
+4. If you previously interpreted “ownership flapping” via ConfirmOwner logs, now check for:
+   - Rapid changes in ring epoch (cart_ring_epoch)
+   - Host churn (cart_ring_hosts)
+   - Imbalance in vnode distribution (cart_ring_host_share)
+
+No data migration is necessary; cart IDs and grain state are unaffected.
+
+---
+
 A distributed cart management system using the actor model pattern.
 
 ## Prerequisites
@@ -175,4 +206,239 @@ curl --cookie cookies.txt http://localhost:8080/cart/add/TEST-SKU-123
 
 - Always regenerate protobuf Go code after modifying any `.proto` files (messages/cart_actor/control_plane)
 - The generated `messages.pb.go` file should not be edited manually
-- Make sure your PATH includes the protoc-gen-go binary location (usually `$GOPATH/bin`)
+- Make sure your PATH includes the protoc-gen-go binary location (usually `$GOPATH/bin`)
+
+---
+
+## Architecture Overview
+
+The system is a distributed, sharded (by cart id) actor model implementation:
+
+- Each cart is a grain (an in‑memory struct `*CartGrain`) that owns and mutates its own state.
+- A **local grain pool** holds grains owned by the node.
+- A **synced (cluster) pool** (`SyncedPool`) coordinates multiple nodes and exposes local or remote grains through a uniform interface (`GrainPool`).
+- All inter‑node communication is gRPC:
+  - Cart mutation & state RPCs (CartActor service).
+  - Control plane RPCs (ControlPlane service) for membership, ownership negotiation, liveness, and graceful shutdown.
+
+### Key Processes
+
+1. Client HTTP request (or gRPC client) arrives with a cart identifier (cookie or path).
+2. The pool resolves ownership:
+   - If local grain exists → use it.
+   - If a remote host is known owner → a remote grain proxy (`RemoteGrainGRPC`) is used; it performs gRPC calls to the owning node.
+   - If ownership is unknown → node attempts to claim ownership (quorum negotiation) and spawns a local grain.
+3. Mutation is executed via the **mutation registry** (registry wraps domain logic + optional totals recomputation).
+4. Updated state returned to caller; ownership preserved unless relinquished later (not yet implemented to shed load).
+
+---
+
+## Grain & Mutation Model
+
+- `CartGrain` holds items, deliveries, pricing aggregates, and checkout/order metadata.
+- All mutations are registered via `RegisterMutation[T]` with signature:
+  ```
+  func(*CartGrain, *T) error
+  ```
+- `WithTotals()` flag triggers automatic recalculation of totals after successful handlers.
+- The old giant `switch` in `CartGrain.Apply` has been replaced by registry dispatch; unregistered mutations fail fast.
+- Adding a mutation:
+  1. Define proto message.
+  2. Generate code.
+  3. Register handler (optionally WithTotals).
+  4. Add gRPC RPC + request wrapper if the mutation must be remotely invokable.
+  5. (Optional) Add HTTP endpoint mapping to the mutation.
+
+---
+
+## Local Grain Pool
+
+- Manages an in‑memory map `map[CartId]*CartGrain`.
+- Lazy spawn: first mutation or explicit access triggers `spawn(id)`.
+- TTL / purge loop periodically removes expired grains unless they changed recently (basic memory pressure management).
+- Capacity limit (`PoolSize`); oldest expired grain evicted first when full.
+
+---
+
+## Synced (Cluster) Pool
+
+`SyncedPool` wraps a local pool and tracks:
+
+- `remoteHosts`: known peer nodes (gRPC connections).
+- `remoteIndex`: mapping of cart id → remote grain proxy (`RemoteGrainGRPC`) for carts owned elsewhere.
+
+Responsibilities:
+
+1. Discovery integration (via a `Discovery` interface) adds/removes hosts.
+2. Periodic ping health checks (ControlPlane.Ping).
+3. Ring-based deterministic ownership:
+   - Ownership is derived directly from the consistent hashing ring (no quorum RPC or `ConfirmOwner`).
+4. Remote spawning:
+   - When a remote host reports its cart ids (`GetCartIds`), the pool creates remote proxies for fast routing.
+
+---
+
+## Remote Grain Proxies
+
+A `RemoteGrainGRPC` implements the `Grain` interface but delegates:
+
+- `Apply` → Specific CartActor per‑mutation RPC (e.g., `AddItem`, `RemoveItem`) constructed from the mutation type. (Legacy envelope removed.)
+- `GetCurrentState` → `CartActor.GetState`.
+
+Return path:
+
+1. gRPC reply (CartMutationReply / StateReply) → proto `CartState`.
+2. `ToCartState` / mapping reconstructs a local `CartGrain` snapshot for callers expecting grain semantics.
+
+---
+
+## Control Plane (Inter‑Node Coordination)
+
+Defined in `proto/control_plane.proto`:
+
+| RPC | Purpose |
+|-----|---------|
+| `Ping` | Liveness; increments missed ping counter if failing. |
+| `Negotiate` | Merges membership views; used after discovery events. |
+| `GetCartIds` | Enumerate locally owned carts for remote index seeding. |
+| `Closing` | Graceful shutdown notice; peers remove host & associated remote grains. |
+
+### Ownership / Quorum Rules
+
+- If total participating hosts < 3 → all must accept.
+- Otherwise majority acceptance (`ok >= total/2`).
+- On failure → local tentative grain is removed (rollback to avoid split‑brain).
+
+---
+
+## Request / Mutation Flow Examples
+
+### Local Mutation
+1. HTTP handler parses request → determines cart id.
+2. `SyncedPool.Apply`:
+   - Finds local grain (or spawns new after quorum).
+   - Executes registry mutation.
+3. Totals updated if flagged.
+4. HTTP response returns updated JSON (via `ToCartState`).
+
+### Remote Mutation
+1. `SyncedPool.Apply` sees cart mapped to a remote host.
+2. Routes to `RemoteGrainGRPC.Apply`.
+3. Remote node executes mutation locally and returns updated state over gRPC.
+4. Proxy materializes snapshot locally (not authoritative, read‑only view).
+
+### Checkout (Side‑Effecting, Non-Pure)
+- HTTP `/checkout` uses current grain snapshot to build payload (pure function).
+- Calls Klarna externally (not a mutation).
+- Applies `InitializeCheckout` mutation to persist reference + status.
+- Returns Klarna order JSON to client.
+
+---
+
+## Scaling & Deployment
+
+- **Horizontal scaling**: Add more nodes; discovery layer (Kubernetes / service registry) feeds hosts to `SyncedPool`.
+- **Sharding**: Implicit by cart id hash. Ownership is first-claim with quorum acceptance.
+- **Hot spots**: A single popular cart remains on one node; for heavy multi-client concurrency, future work could add read replicas or partitioning (not implemented).
+- **Capacity tuning**: Increase `PoolSize` & memory limits; adjust TTL for stale cart eviction.
+
+### Adding Nodes
+1. Node starts gRPC server (CartActor + ControlPlane).
+2. After brief delay, begins discovery watch; on event:
+   - New host → dial + negotiate → seed remote cart ids.
+3. Pings maintain health; failed hosts removed (proxies invalidated).
+
+---
+
+## Failure Handling
+
+| Scenario | Behavior |
+|----------|----------|
+| Remote host unreachable | Pings increment `MissedPings`; after threshold host removed. |
+| Ownership negotiation fails | Tentative local grain discarded. |
+| gRPC call error on remote mutation | Error bubbled to caller; no local fallback. |
+| Missing mutation registration | Fast failure with explicit error message. |
+| Partial checkout (Klarna fails) | No local state mutation for checkout; client sees error; cart remains unchanged. |
+
+---
+
+## Mutation Registry Summary
+
+- Central, type-safe registry prevents silent omission.
+- Each handler:
+  - Validates input.
+  - Mutates `*CartGrain`.
+  - Returns error for rejection.
+- Automatic totals recomputation reduces boilerplate and consistency risk.
+- Coverage test (add separately) can enforce all proto mutations are registered.
+
+---
+
+## gRPC Interfaces
+
+- **CartActor**: Per-mutation unary RPCs + `GetState`. (Checkout logic intentionally excluded; handled at HTTP layer.)
+- **ControlPlane**: Cluster coordination (Ping, Negotiate, GetCartIds, Closing) — ownership now ring-determined (no ConfirmOwner).
+
+**Ports** (default / implied):
+- CartActor & ControlPlane share the same gRPC server/listener (single port, e.g. `:1337`).
+- Legacy frame/TCP code has been removed.
+
+---
+
+## Security & Future Enhancements
+
+| Area | Potential Improvement |
+|------|------------------------|
+| Transport Security | Add TLS / mTLS to gRPC servers & clients. |
+| Auth / RBAC | Intercept CartActor RPCs with auth metadata. |
+| Backpressure | Rate-limit remote mutation calls per host. |
+| Observability | Add per-mutation Prometheus metrics & tracing spans. |
+| Ownership | Add lease timeouts / fencing tokens for stricter guarantees. |
+| Batch Ops | Introduce batch mutation RPC or streaming updates (WatchState). |
+| Persistence | Reintroduce event log or snapshot persistence layer if durability required. |
+
+---
+
+## Adding a New Node (Operational Checklist)
+
+1. Deploy binary/container with same proto + registry.
+2. Expose gRPC port.
+3. Ensure discovery lists the new host.
+4. Node dials peers, negotiates membership.
+5. Remote cart proxies seeded.
+6. Traffic routed automatically based on ownership.
+
+---
+
+## Adding a New Mutation (Checklist Recap)
+
+1. Define proto message (+ request wrapper & RPC if remote invocation needed).
+2. Regenerate protobuf code.
+3. Implement & register handler (`RegisterMutation`).
+4. Add client (HTTP/gRPC) endpoint.
+5. Write unit + integration tests.
+6. (Optional) Add to coverage test list and docs.
+
+---
+
+## High-Level Data Flow Diagram (Text)
+
+```
+Client -> HTTP Handler -> SyncedPool -> (local?) -> Registry -> Grain State
+                       \-> (remote?) -> RemoteGrainGRPC -> gRPC -> Remote CartActor -> Registry -> Grain
+ControlPlane: Discovery Events <-> Negotiation/Ping <-> SyncedPool state (ring determines ownership)
+```
+
+---
+
+## Troubleshooting
+
+| Symptom | Likely Cause | Action |
+|---------|--------------|--------|
+| New cart every request | Secure cookie over plain HTTP or not sending cookie jar | Disable Secure locally or use HTTPS & proper curl `-b` |
+| Unsupported mutation error | Missing registry handler | Add `RegisterMutation` for that proto |
+| Ownership imbalance | Ring host distribution skew or rapid host churn | Examine `cart_ring_host_share`, `cart_ring_hosts`, and logs for host add/remove; rebalance or investigate instability |
+| Remote mutation latency | Network / serialization overhead | Consider batching or colocating hot carts |
+| Checkout returns 500 | Klarna call failed | Inspect logs; no grain state mutated |
+
+---

TODO.md

@@ -0,0 +1,245 @@
+# TODO / Roadmap
+
+A living roadmap for improving the cart actor system. Focus areas:
+1. Reliability & correctness
+2. Simplicity of mutation & ownership flows
+3. Developer experience (DX)
+4. Operability (observability, tracing, metrics)
+5. Performance & scalability
+6. Security & multi-tenant readiness
+
+---
+
+## 1. Immediate Next Steps (High-Leverage)
+
+| Priority | Task | Goal | Effort | Owner | Notes |
+|----------|------|------|--------|-------|-------|
+| P0 | Add mutation registry coverage test | Ensure no unregistered mutations silently fail | S |  | Failing fast in CI |
+| P0 | Add decodeJSON helper + 400 mapping for EOF | Reduce noisy 500 logs | S |  | Improves client API clarity |
+| P0 | Regenerate protos & prune unused messages (CreateCheckoutOrder, Checkout RPC remnants) | Eliminate dead types | S |  | Avoid confusion |
+| P0 | Add integration test: multi-node ownership negotiation | Validate quorum logic | M |  | Spin up 2–3 nodes ephemeral |
+| P1 | Export Prometheus metrics for per-mutation counts & latency | Operability | M |  | Wrap registry handlers |
+| P1 | Add graceful shutdown ordering (Closing → wait for acks → stop gRPC) | Reduce in-flight mutation failures | S |  | Add context cancellation |
+| P1 | Add coverage for InitializeCheckout / OrderCreated flows | Checkout reliability | S |  | Simulate Klarna stub |
+| P2 | Add optional batching client (apply multiple mutations locally then persist) | Performance | M |  | Only if needed |
+
+---
+
+## 2. Simplification Opportunities
+
+### A. RemoteGrain Proxy Mapping
+Current: manual switch building each RPC call.
+Simplify by:
+- Generating a thin client adapter from proto RPC descriptors (codegen).
+- Or using a registry similar to mutation registry but for “outbound call constructors”.
+Benefit: adding a new mutation = add proto + register server handler + register outbound invoker (no switch edits).
+
+### B. Ownership Negotiation
+Current: ad hoc quorum rule in `SyncedPool`.
+Simplify:
+- Introduce explicit `OwnershipLease{holder, expiresAt, version}`.
+- Use monotonic version increment—reject stale ConfirmOwner replies.
+- Optional: add randomized backoff to reduce thundering herd on contested cart ids.
+
+### C. CartId Handling
+Current: ephemeral 16-byte array with trimmed string semantics.
+Simplify:
+- Use ULID / UUIDv7 (time-ordered, collision-resistant) for easier external correlation.
+- Provide helper `NewCartIdString()` and keep internal fixed-size if still desired.
+
+### D. Mutation Signatures
+Current: registry assumes `func(*CartGrain, *T) error`.
+Extension option: allow pure transforms returning a delta struct (for audit/logging):
+```
+type MutationResult struct {
+  Changed bool
+  Events  []interface{}
+}
+```
+Only implement if auditing/event-sourcing reintroduced.
+
+---
+
+## 3. Developer Experience Improvements
+
+| Task | Rationale | Approach |
+|------|-----------|----------|
+| Makefile targets: `make run-single`, `make run-multi N=3` | Faster local cluster spin-up | Docker compose or background “mini cluster” scripts |
+| Template for new mutation (generator) | Reduce boilerplate | `go:generate` scanning proto for new RPCs |
+| Lint config (golangci-lint) | Catch subtle issues early | Add `.golangci.yml` |
+| Pre-commit hook for proto regeneration check | Avoid stale generated code | Script compares git diff after `make protogen` |
+| Example client (Go + curl snippets auto-generated) | Onboarding | Codegen a markdown from proto comments |
+
+---
+
+## 4. Observability / Metrics / Tracing
+
+| Area | Metric / Trace | Notes |
+|------|----------------|-------|
+| Mutation registry | `cart_mutations_total{type,success}`; duration histogram | Wrap handler |
+| Ownership negotiation | `cart_ownership_attempts_total{result}` | result=accepted,rejected,timeout |
+| Remote latency | `cart_remote_mutation_seconds{method}` | Use client interceptors |
+| Pings | `cart_remote_missed_pings_total{host}` | Already count, expose |
+| Checkout flow | `checkout_attempts_total`, `checkout_failures_total` | Differentiate Klarna vs internal errors |
+| Tracing | Span: HTTP handler → SyncedPool.Apply → (Remote?) gRPC → mutation handler | Add OpenTelemetry instrumentation |
+
+---
+
+## 5. Performance & Scalability
+
+| Concern | Idea | Trade-Off |
+|---------|------|-----------|
+| High mutation rate on single cart | Introduce optional mutation queue (serialize explicitly) | Slight latency increase per op |
+| Remote call overhead | Add client-side gRPC pooling & per-host circuit breaker | Complexity vs resilience |
+| TTL purge efficiency | Use min-heap or timing wheel instead of slice scan | More code, better big-N performance |
+| Batch network latency | Add `BatchMutate` RPC (list of mutations applied atomically) | Lost single-op simplicity |
+
+---
+
+## 6. Reliability Features
+
+| Feature | Description | Priority |
+|---------|-------------|----------|
+| Lease fencing token | Include `ownership_version` in all remote mutate requests | M |
+| Retry policy | Limited retry for transient network errors (idempotent mutations only) | L |
+| Dead host reconciliation | On host removal, proactively attempt re-acquire of its carts | M |
+| Drain mode | Node marks itself “draining” → refuses new ownership claims | M |
+
+---
+
+## 7. Security & Hardening
+
+| Area | Next Step | Detail |
+|------|-----------|--------|
+| Transport | mTLS on gRPC | Use SPIFFE IDs or simple CA |
+| AuthN/AuthZ | Interceptor enforcing service token | Inject metadata header |
+| Input validation | Strengthen JSON decode responses | Disallow unknown fields globally |
+| Rate limiting | Per-IP / per-cart throttling | Guard hotspot abuse |
+| Multi-tenancy | Tenant id dimension in cart id or metadata | Partition metrics & ownership |
+
+---
+
+## 8. Testing Strategy Enhancements
+
+| Gap | Improvement |
+|-----|------------|
+| No multi-node integration test in CI | Spin ephemeral in-process servers on randomized ports |
+| Mutation regression | Table-driven tests auto-discover handlers via registry |
+| Ownership race | Stress test: concurrent Apply on same new cart id from N goroutines |
+| Checkout external dependency | Klarna mock server (HTTptest) + deterministic responses |
+| Fuzzing | Fuzz `BuildCheckoutOrderPayload` & mutation handlers for panics |
+
+---
+
+## 9. Cleanup / Tech Debt
+
+| Item | Action |
+|------|--------|
+| Remove deprecated proto remnants (CreateCheckoutOrder, Checkout RPC) | Delete & regenerate |
+| Consolidate duplicate tax computations | Single helper with tax config |
+| Delivery price hard-coded (4900) | Config or pricing strategy interface |
+| Mixed naming (camel vs snake JSON historically) | Provide stable external API doc; accept old forms if needed |
+| Manual remote mutation switch (if still present) | Replace with generated outbound registry |
+| Mixed error responses (string bodies) | Standardize JSON: `{ "error": "...", "code": 400 }` |
+
+---
+
+## 10. Potential Future Features
+
+| Feature | Value | Complexity |
+|---------|-------|------------|
+| Streaming `WatchState` RPC | Real-time cart updates for clients | Medium |
+| Event sourcing / audit log | Replay, analytics, debugging | High |
+| Promotion / coupon engine plugin | Business extensibility | Medium |
+| Partial cart reservation / inventory lock | Stock accuracy under concurrency | High |
+| Multi-currency pricing | Globalization | Medium |
+| GraphQL facade | Client flexibility | Medium |
+
+---
+
+## 11. Suggested Prioritized Backlog (Condensed)
+
+1. Coverage test + decode error mapping (P0)
+2. Proto regeneration & cleanup (P0)
+3. Metrics wrapper for registry (P1)
+4. Multi-node ownership integration test (P1)
+5. Delivery pricing abstraction (P2)
+6. Lease version in remote RPCs (P2)
+7. BatchMutate evaluation (P3)
+8. TLS / auth hardening (P3) if going multi-tenant/public
+9. Event sourcing (Evaluate after stability) (P4)
+
+---
+
+## 12. Simplifying the Developer Workflow
+
+| Pain | Simplifier |
+|------|------------|
+| Manual mutation boilerplate | Code generator for registry stubs |
+| Forgetting totals | Enforce WithTotals lint: fail if mutation touches items/deliveries without flag |
+| Hard to inspect remote ownership | `/internal/ownership` debug endpoint (JSON of local + remoteIndex) |
+| Hard to see mutation timings | Add `?debug=latency` header to return per-mutation durations |
+| Cookie dev confusion (Secure flag) | Env var: `DEV_INSECURE_COOKIES=1` |
+
+---
+
+## 13. Example: Mutation Codegen Sketch (Future)
+
+Input: cart_actor.proto  
+Output: `mutation_auto.go`
+- Detect messages used in RPC wrappers (e.g., `AddItemRequest` → payload field).
+- Generate `RegisterMutation` template if handler not found.
+- Mark with `// TODO implement logic`.
+
+---
+
+## 14. Risk / Impact Matrix (Abbreviated)
+
+| Change | Risk | Mitigation |
+|--------|------|-----------|
+| Replace remote switch with registry | Possible missing registration → runtime error | Coverage test gating CI |
+| Lease introduction | Split-brain if version mishandled | Increment + assert monotonic; test race |
+| BatchMutate | Large atomic operations starving others | Size limits & fair scheduling |
+| Event sourcing | Storage + replay complexity | Start with append-only log + compaction job |
+
+---
+
+## 15. Contributing Workflow (Proposed)
+
+1. Add / modify proto → run `make protogen`
+2. Implement mutation logic → add `RegisterMutation` invocation
+3. Add/Update tests (unit + integration)
+4. Run `make verify` (lint, test, coverage, proto diff)
+5. Open PR (template auto-checklist referencing this TODO)
+6. Merge requires green CI + coverage threshold
+
+---
+
+## 16. Open Questions
+
+| Question | Notes |
+|----------|-------|
+| Do we need sticky sessions for HTTP layer scaling? | Currently cart id routing suffices |
+| Should deliveries prune invalid line references on SetCartRequest? | Inconsistency risk; add optional cleanup |
+| Is checkout idempotency strict enough? | Multiple create vs update semantics |
+| Add version field to CartState for optimistic concurrency? | Could enable external CAS writes |
+
+---
+
+## 17. Tracking
+
+Mark any completed tasks with `[x]`:
+
+- [ ] Coverage test
+- [ ] Decode helper + 400 mapping
+- [ ] Proto cleanup
+- [ ] Registry metrics instrumentation
+- [ ] Ownership multi-node test
+- [ ] Lease versioning
+- [ ] Delivery pricing abstraction
+- [ ] TLS/mTLS internal
+- [ ] BatchMutate design doc
+
+---
+
+_Last updated: roadmap draft – refine after first metrics & scaling test run._

amqp-order-handler.go

@@ -1,83 +1,61 @@
 package main
 
 import (
-	"log"
+	"context"
+	"fmt"
+	"time"
 
 	amqp "github.com/rabbitmq/amqp091-go"
 )
 
 type AmqpOrderHandler struct {
 	Url        string
-	connection *amqp.Connection
+	Connection *amqp.Connection
-	//channel    *amqp.Channel
+	Channel    *amqp.Channel
 }
 
-const (
+func (h *AmqpOrderHandler) Connect() error {
-	topic = "order-placed"
+	conn, err := amqp.Dial(h.Url)
-)
-
-func (t *AmqpOrderHandler) Connect() error {
-
-	conn, err := amqp.DialConfig(t.Url, amqp.Config{
-		//Vhost:      "/",
-		Properties: amqp.NewConnectionProperties(),
-	})
-
 	if err != nil {
-		return err
+		return fmt.Errorf("failed to connect to RabbitMQ: %w", err)
 	}
-	t.connection = conn
+	h.Connection = conn
+
 	ch, err := conn.Channel()
 	if err != nil {
-		return err
+		return fmt.Errorf("failed to open a channel: %w", err)
-	}
-	defer ch.Close()
-	if err := ch.ExchangeDeclare(
-		topic,   // name
-		"topic", // type
-		true,    // durable
-		false,   // auto-delete
-		false,   // internal
-		false,   // noWait
-		nil,     // arguments
-	); err != nil {
-		return err
-	}
-
-	if _, err = ch.QueueDeclare(
-		topic, // name of the queue
-		true,  // durable
-		false, // delete when unused
-		false, // exclusive
-		false, // noWait
-		nil,   // arguments
-	); err != nil {
-		return err
 	}
+	h.Channel = ch
 
 	return nil
 }
 
-func (t *AmqpOrderHandler) Close() error {
+func (h *AmqpOrderHandler) Close() error {
-	log.Println("Closing master channel")
+	if h.Channel != nil {
-	return t.connection.Close()
+		h.Channel.Close()
-	//return t.channel.Close()
+	}
+	if h.Connection != nil {
+		return h.Connection.Close()
+	}
+	return nil
 }
 
-func (t *AmqpOrderHandler) OrderCompleted(data []byte) error {
+func (h *AmqpOrderHandler) OrderCompleted(body []byte) error {
-	ch, err := t.connection.Channel()
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
-	if err != nil {
+	defer cancel()
-		return err
+
-	}
+	err := h.Channel.PublishWithContext(ctx,
-	defer ch.Close()
+		"orders", // exchange
-	return ch.Publish(
+		"new",    // routing key
-		topic,
+		false,    // mandatory
-		topic,
+		false,    // immediate
-		true,
-		false,
 		amqp.Publishing{
 			ContentType: "application/json",
-			Body:        data,
+			Body:        body,
-		},
+		})
-	)
+	if err != nil {
+		return fmt.Errorf("failed to publish a message: %w", err)
+	}
+
+	return nil
 }

cart-grain.go

@@ -1,13 +1,9 @@
 package main
 
 import (
-	"bytes"
 	"encoding/json"
 	"fmt"
-	"log"
-	"slices"
 	"sync"
-	"time"
 
 	messages "git.tornberg.me/go-cart-actor/proto"
 )
@@ -93,7 +89,6 @@ type CartGrain struct {
 	mu                sync.RWMutex
 	lastItemId        int
 	lastDeliveryId    int
-	storageMessages   []Message
 	Id                CartId          `json:"id"`
 	Items             []*CartItem     `json:"items"`
 	TotalPrice        int64           `json:"totalPrice"`
@@ -108,8 +103,8 @@ type CartGrain struct {
 
 type Grain interface {
 	GetId() CartId
-	HandleMessage(message *Message, isReplay bool) (*FrameWithPayload, error)
+	Apply(content interface{}, isReplay bool) (*CartGrain, error)
-	GetCurrentState() (*FrameWithPayload, error)
+	GetCurrentState() (*CartGrain, error)
 }
 
 func (c *CartGrain) GetId() CartId {
@@ -117,20 +112,12 @@ func (c *CartGrain) GetId() CartId {
 }
 
 func (c *CartGrain) GetLastChange() int64 {
-	if len(c.storageMessages) == 0 {
+	// Legacy event log removed; return 0 to indicate no persisted mutation history.
-		return 0
+	return 0
-	}
-	return *c.storageMessages[len(c.storageMessages)-1].TimeStamp
 }
 
-func (c *CartGrain) GetCurrentState() (*FrameWithPayload, error) {
+func (c *CartGrain) GetCurrentState() (*CartGrain, error) {
-	result, err := json.Marshal(c)
+	return c, nil
-	if err != nil {
-		ret := MakeFrameWithPayload(0, 400, []byte(err.Error()))
-		return &ret, nil
-	}
-	ret := MakeFrameWithPayload(0, 200, result)
-	return &ret, nil
 }
 
 func getInt(data float64, ok bool) (int, error) {
@@ -201,30 +188,23 @@ func getItemData(sku string, qty int, country string) (*messages.AddItem, error)
 	}, nil
 }
 
-func (c *CartGrain) AddItem(sku string, qty int, country string, storeId *string) (*FrameWithPayload, error) {
+func (c *CartGrain) AddItem(sku string, qty int, country string, storeId *string) (*CartGrain, error) {
 	cartItem, err := getItemData(sku, qty, country)
 	if err != nil {
 		return nil, err
 	}
 	cartItem.StoreId = storeId
-	return c.HandleMessage(&Message{
+	return c.Apply(cartItem, false)
-		Type:    2,
-		Content: cartItem,
-	}, false)
 }
 
-func (c *CartGrain) GetStorageMessage(since int64) []StorableMessage {
+/*
-	c.mu.RLock()
+Legacy storage (event sourcing) removed in oneof refactor.
-	defer c.mu.RUnlock()
+Kept stub (commented) for potential future reintroduction using proto envelopes.
-	ret := make([]StorableMessage, 0)
 
-	for _, message := range c.storageMessages {
+func (c *CartGrain) GetStorageMessage(since int64) []interface{} {
-		if *message.TimeStamp > since {
+	return nil
-			ret = append(ret, message)
-		}
-	}
-	return ret
 }
+*/
 
 func (c *CartGrain) GetState() ([]byte, error) {
 	return json.Marshal(c)
@@ -279,324 +259,17 @@ func GetTaxAmount(total int64, tax int) int64 {
 	return int64(float64(total) / float64((1 + taxD)))
 }
 
-func (c *CartGrain) HandleMessage(message *Message, isReplay bool) (*FrameWithPayload, error) {
+func (c *CartGrain) Apply(content interface{}, isReplay bool) (*CartGrain, error) {
-	if message.TimeStamp == nil {
-		now := time.Now().Unix()
-		message.TimeStamp = &now
-	}
 	grainMutations.Inc()
-	var err error
-	switch message.Type {
-	case SetCartItemsType:
-		msg, ok := message.Content.(*messages.SetCartRequest)
-		if !ok {
-			err = fmt.Errorf("expected SetCartItems")
-		} else {
 
-			c.mu.Lock()
+	updated, err := ApplyRegistered(c, content)
-			c.Items = make([]*CartItem, 0, len(msg.Items))
-			c.mu.Unlock()
-			for _, item := range msg.Items {
-				c.AddItem(item.Sku, int(item.Quantity), item.Country, item.StoreId)
-			}
-
-		}
-	case AddRequestType:
-		msg, ok := message.Content.(*messages.AddRequest)
-		if !ok {
-			err = fmt.Errorf("expected AddRequest")
-		} else {
-
-			existingItem, found := c.FindItemWithSku(msg.Sku)
-			if found {
-				existingItem.Quantity += int(msg.Quantity)
-				c.UpdateTotals()
-			} else {
-				return c.AddItem(msg.Sku, int(msg.Quantity), msg.Country, msg.StoreId)
-			}
-
-		}
-	case AddItemType:
-		msg, ok := message.Content.(*messages.AddItem)
-		if !ok {
-			err = fmt.Errorf("expected AddItem")
-		} else {
-
-			if msg.Quantity < 1 {
-				return nil, fmt.Errorf("invalid quantity")
-			}
-			existingItem, found := c.FindItemWithSku(msg.Sku)
-			if found {
-				existingItem.Quantity += int(msg.Quantity)
-				c.UpdateTotals()
-			} else {
-				c.mu.Lock()
-				c.lastItemId++
-				tax := 2500
-				if msg.Tax > 0 {
-					tax = int(msg.Tax)
-				}
-
-				taxAmount := GetTaxAmount(msg.Price, tax)
-
-				c.Items = append(c.Items, &CartItem{
-					Id:          c.lastItemId,
-					ItemId:      int(msg.ItemId),
-					Quantity:    int(msg.Quantity),
-					Sku:         msg.Sku,
-					Name:        msg.Name,
-					Price:       msg.Price,
-					TotalPrice:  msg.Price * int64(msg.Quantity),
-					TotalTax:    int64(taxAmount * int64(msg.Quantity)),
-					Image:       msg.Image,
-					Stock:       StockStatus(msg.Stock),
-					Disclaimer:  msg.Disclaimer,
-					Brand:       msg.Brand,
-					Category:    msg.Category,
-					Category2:   msg.Category2,
-					Category3:   msg.Category3,
-					Category4:   msg.Category4,
-					Category5:   msg.Category5,
-					OrgPrice:    msg.OrgPrice,
-					ArticleType: msg.ArticleType,
-					Outlet:      msg.Outlet,
-					SellerId:    msg.SellerId,
-					SellerName:  msg.SellerName,
-					Tax:         int(taxAmount),
-					TaxRate:     tax,
-					StoreId:     msg.StoreId,
-				})
-				c.UpdateTotals()
-				c.mu.Unlock()
-			}
-
-		}
-	case ChangeQuantityType:
-		msg, ok := message.Content.(*messages.ChangeQuantity)
-		if !ok {
-			err = fmt.Errorf("expected ChangeQuantity")
-		} else {
-
-			for i, item := range c.Items {
-				if item.Id == int(msg.Id) {
-					if msg.Quantity <= 0 {
-						//c.TotalPrice -= item.Price * int64(item.Quantity)
-						c.Items = append(c.Items[:i], c.Items[i+1:]...)
-					} else {
-						//diff := int(msg.Quantity) - item.Quantity
-						item.Quantity = int(msg.Quantity)
-						//c.TotalPrice += item.Price * int64(diff)
-					}
-
-					break
-				}
-			}
-			c.UpdateTotals()
-
-		}
-	case RemoveItemType:
-		msg, ok := message.Content.(*messages.RemoveItem)
-		if !ok {
-			err = fmt.Errorf("expected RemoveItem")
-		} else {
-
-			items := make([]*CartItem, 0, len(c.Items))
-			for _, item := range c.Items {
-				if item.Id == int(msg.Id) {
-					//c.TotalPrice -= item.Price * int64(item.Quantity)
-				} else {
-					items = append(items, item)
-				}
-			}
-			c.Items = items
-			c.UpdateTotals()
-		}
-	case SetDeliveryType:
-		msg, ok := message.Content.(*messages.SetDelivery)
-		if !ok {
-			err = fmt.Errorf("expected SetDelivery")
-		} else {
-
-			c.lastDeliveryId++
-			items := make([]int, 0)
-			withDelivery := c.ItemsWithDelivery()
-			if len(msg.Items) == 0 {
-				items = append(items, c.ItemsWithoutDelivery()...)
-			} else {
-				for _, id := range msg.Items {
-					for _, item := range c.Items {
-						if item.Id == int(id) {
-							if slices.Contains(withDelivery, item.Id) {
-								return nil, fmt.Errorf("item already has delivery")
-							}
-							items = append(items, int(item.Id))
-							break
-						}
-					}
-				}
-			}
-			if len(items) > 0 {
-				c.Deliveries = append(c.Deliveries, &CartDelivery{
-					Id:          c.lastDeliveryId,
-					Provider:    msg.Provider,
-					PickupPoint: msg.PickupPoint,
-					Price:       4900,
-					Items:       items,
-				})
-
-				c.UpdateTotals()
-
-			}
-
-		}
-	case RemoveDeliveryType:
-		msg, ok := message.Content.(*messages.RemoveDelivery)
-		if !ok {
-			err = fmt.Errorf("expected RemoveDelivery")
-		} else {
-
-			deliveries := make([]*CartDelivery, 0, len(c.Deliveries))
-			for _, delivery := range c.Deliveries {
-				if delivery.Id == int(msg.Id) {
-					c.TotalPrice -= delivery.Price
-				} else {
-					deliveries = append(deliveries, delivery)
-				}
-			}
-			c.Deliveries = deliveries
-			c.UpdateTotals()
-		}
-	case SetPickupPointType:
-		msg, ok := message.Content.(*messages.SetPickupPoint)
-		if !ok {
-			err = fmt.Errorf("expected SetPickupPoint")
-		} else {
-
-			for _, delivery := range c.Deliveries {
-				if delivery.Id == int(msg.DeliveryId) {
-					delivery.PickupPoint = &messages.PickupPoint{
-						Id:      msg.Id,
-						Address: msg.Address,
-						City:    msg.City,
-						Zip:     msg.Zip,
-						Country: msg.Country,
-						Name:    msg.Name,
-					}
-					break
-				}
-			}
-
-		}
-	case CreateCheckoutOrderType:
-		msg, ok := message.Content.(*messages.CreateCheckoutOrder)
-		if !ok {
-			err = fmt.Errorf("expected CreateCheckoutOrder")
-		} else {
-
-			orderLines := make([]*Line, 0, len(c.Items))
-
-			c.PaymentInProgress = true
-			c.Processing = true
-			for _, item := range c.Items {
-
-				orderLines = append(orderLines, &Line{
-					Type:           "physical",
-					Reference:      item.Sku,
-					Name:           item.Name,
-					Quantity:       item.Quantity,
-					UnitPrice:      int(item.Price),
-					TaxRate:        2500, // item.TaxRate,
-					QuantityUnit:   "st",
-					TotalAmount:    int(item.TotalPrice),
-					TotalTaxAmount: int(item.TotalTax),
-					ImageURL:       fmt.Sprintf("https://www.elgiganten.se%s", item.Image),
-				})
-			}
-			for _, line := range c.Deliveries {
-				if line.Price > 0 {
-					orderLines = append(orderLines, &Line{
-						Type:           "shipping_fee",
-						Reference:      line.Provider,
-						Name:           "Delivery",
-						Quantity:       1,
-						UnitPrice:      int(line.Price),
-						TaxRate:        2500, // item.TaxRate,
-						QuantityUnit:   "st",
-						TotalAmount:    int(line.Price),
-						TotalTaxAmount: int(GetTaxAmount(line.Price, 2500)),
-					})
-				}
-			}
-			order := CheckoutOrder{
-				PurchaseCountry:    "SE",
-				PurchaseCurrency:   "SEK",
-				Locale:             "sv-se",
-				OrderAmount:        int(c.TotalPrice),
-				OrderTaxAmount:     int(c.TotalTax),
-				OrderLines:         orderLines,
-				MerchantReference1: c.Id.String(),
-				MerchantURLS: &CheckoutMerchantURLS{
-					Terms:        msg.Terms,
-					Checkout:     msg.Checkout,
-					Confirmation: msg.Confirmation,
-					Validation:   msg.Validation,
-					Push:         msg.Push,
-				},
-			}
-			orderPayload, err := json.Marshal(order)
-			if err != nil {
-				return nil, err
-			}
-			var klarnaOrder *CheckoutOrder
-			if c.OrderReference != "" {
-				log.Printf("Updating order id %s", c.OrderReference)
-				klarnaOrder, err = KlarnaInstance.UpdateOrder(c.OrderReference, bytes.NewReader(orderPayload))
-			} else {
-				klarnaOrder, err = KlarnaInstance.CreateOrder(bytes.NewReader(orderPayload))
-			}
-			// log.Printf("Order result: %+v", klarnaOrder)
-			if nil != err {
-				log.Printf("error from klarna: %v", err)
-				return nil, err
-			}
-			if c.OrderReference == "" {
-				c.OrderReference = klarnaOrder.ID
-				c.PaymentStatus = klarnaOrder.Status
-			}
-
-			orderData, err := json.Marshal(klarnaOrder)
-			if nil != err {
-				return nil, err
-			}
-
-			result := MakeFrameWithPayload(RemoteCreateOrderReply, 200, orderData)
-			return &result, nil
-		}
-	case OrderCompletedType:
-		msg, ok := message.Content.(*messages.OrderCreated)
-		if !ok {
-			log.Printf("expected OrderCompleted, got %T", message.Content)
-			err = fmt.Errorf("expected OrderCompleted")
-		} else {
-			c.OrderReference = msg.OrderId
-			c.PaymentStatus = msg.Status
-			c.PaymentInProgress = false
-		}
-	default:
-		err = fmt.Errorf("unknown message type %d", message.Type)
-	}
 	if err != nil {
+		if err == ErrMutationNotRegistered {
+			return nil, fmt.Errorf("unsupported mutation type %T (not registered)", content)
+		}
 		return nil, err
 	}
-
+	return updated, nil
-	if !isReplay {
-		c.mu.Lock()
-		c.storageMessages = append(c.storageMessages, *message)
-		c.mu.Unlock()
-	}
-	result, err := json.Marshal(c)
-	msg := MakeFrameWithPayload(RemoteHandleMutationReply, 200, result)
-	return &msg, err
 }
 
 func (c *CartGrain) UpdateTotals() {

cart_id.go

@@ -0,0 +1,327 @@
+package main
+
+import (
+	"crypto/rand"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"strings"
+)
+
+// cart_id.go
+//
+// Compact CartID implementation using 64 bits of cryptographic randomness,
+// base62 encoded (0-9 A-Z a-z). Typical length is 11 characters (since 62^11 > 2^64).
+//
+// Motivation:
+//   * Shorter identifiers for cookies / URLs than legacy padded 16-byte CartId
+//   * O(1) hashing (raw uint64) for consistent hashing ring integration
+//   * Extremely low collision probability (birthday bound negligible at scale)
+//
+// Backward Compatibility Strategy (Phased):
+//   Phase 1: Introduce CartID helpers while continuing to accept legacy CartId.
+//   Phase 2: Internally migrate maps to key by uint64 (CartID.Raw()).
+//   Phase 3: Canonicalize all inbound IDs to short base62; reissue Set-Cart-Id header.
+//
+// NOTE:
+//   The legacy type `CartId [16]byte` is still present elsewhere; helper
+//   UpgradeLegacyCartId bridges that representation to the new form without
+//   breaking deterministic mapping for existing carts.
+//
+// Security / Predictability:
+//   Uses crypto/rand for generation. If ever required, you can layer an
+//   HMAC-based derivation for additional secrecy. Current approach already
+//   provides 64 bits of entropy (brute force infeasible for practical risk).
+//
+// Future Extensions:
+//   * Time-sortable IDs: prepend a 48-bit timestamp field and encode 80 bits.
+//   * Add metrics counters for: generated_new, parsed_existing, legacy_fallback.
+//   * Add a pool of pre-generated IDs for ultra-low-latency hot paths (rarely needed).
+//
+// Public Surface Summary:
+//   NewCartID() (CartID, error)
+//   ParseCartID(string) (CartID, bool)
+//   FallbackFromString(string) CartID
+//   UpgradeLegacyCartId(CartId) CartID
+//   CanonicalizeIncoming(string) (CartID, bool /*wasGenerated*/, error)
+//
+// Encoding Details:
+//   encodeBase62 / decodeBase62 maintain a stable alphabet. DO NOT change
+//   alphabet order once IDs are in circulation, or previously issued IDs
+//   will change meaning.
+//
+// Zero Values:
+//   The zero value CartID{} has raw=0, txt="0". Treat it as valid but
+//   usually you will call NewCartID instead.
+//
+// ---------------------------------------------------------------------------
+
+const base62Alphabet = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
+
+// Precomputed reverse lookup table for decode (255 = invalid).
+var base62Rev [256]byte
+
+func init() {
+	for i := range base62Rev {
+		base62Rev[i] = 0xFF
+	}
+	for i := 0; i < len(base62Alphabet); i++ {
+		base62Rev[base62Alphabet[i]] = byte(i)
+	}
+}
+
+// CartID is the compact representation of a cart identifier.
+// raw: 64-bit entropy (also used directly for consistent hashing).
+// txt: cached base62 textual form.
+type CartID struct {
+	raw uint64
+	txt string
+}
+
+// String returns the canonical base62 encoded ID.
+func (c CartID) String() string {
+	if c.txt == "" { // lazily encode if constructed manually
+		c.txt = encodeBase62(c.raw)
+	}
+	return c.txt
+}
+
+// Raw returns the 64-bit numeric value (useful for hashing / ring lookup).
+func (c CartID) Raw() uint64 {
+	return c.raw
+}
+
+// IsZero reports whether this CartID is the zero value.
+func (c CartID) IsZero() bool {
+	return c.raw == 0
+}
+
+// NewCartID generates a new cryptographically random 64-bit ID.
+func NewCartID() (CartID, error) {
+	var b [8]byte
+	if _, err := rand.Read(b[:]); err != nil {
+		return CartID{}, fmt.Errorf("NewCartID: %w", err)
+	}
+	u := binary.BigEndian.Uint64(b[:])
+	// Reject zero if you want to avoid ever producing "0" (optional).
+	if u == 0 {
+		// Extremely unlikely; recurse once.
+		return NewCartID()
+	}
+	return CartID{raw: u, txt: encodeBase62(u)}, nil
+}
+
+// MustNewCartID panics on failure (suitable for tests / initialization).
+func MustNewCartID() CartID {
+	id, err := NewCartID()
+	if err != nil {
+		panic(err)
+	}
+	return id
+}
+
+// ParseCartID attempts to parse a base62 canonical ID.
+// Returns (id, true) if fully valid; (zero, false) otherwise.
+func ParseCartID(s string) (CartID, bool) {
+	if len(s) == 0 {
+		return CartID{}, false
+	}
+	// Basic length sanity; allow a bit of headroom for future timestamp variant.
+	if len(s) > 16 {
+		return CartID{}, false
+	}
+	u, ok := decodeBase62(s)
+	if !ok {
+		return CartID{}, false
+	}
+	return CartID{raw: u, txt: s}, true
+}
+
+// FallbackFromString produces a deterministic CartID from arbitrary input
+// using a 64-bit FNV-1a hash. This allows legacy or malformed IDs to map
+// consistently into the new scheme (collision probability still low).
+func FallbackFromString(s string) CartID {
+	const (
+		offset64 = 1469598103934665603
+		prime64  = 1099511628211
+	)
+	h := uint64(offset64)
+	for i := 0; i < len(s); i++ {
+		h ^= uint64(s[i])
+		h *= prime64
+	}
+	return CartID{raw: h, txt: encodeBase62(h)}
+}
+
+// UpgradeLegacyCartId converts the old 16-byte CartId (padded) to CartID
+// by hashing its trimmed string form. Keeps stable mapping across restarts.
+func UpgradeLegacyCartId(old CartId) CartID {
+	return FallbackFromString(old.String())
+}
+
+// CanonicalizeIncoming normalizes user-provided ID strings.
+// Behavior:
+//
+//	Empty string  -> generate new ID (wasGenerated = true)
+//	Valid base62  -> parse and return (wasGenerated = false)
+//	Anything else -> fallback deterministic hash (wasGenerated = false)
+//
+// Errors only occur if crypto/rand fails during generation.
+func CanonicalizeIncoming(s string) (CartID, bool, error) {
+	if s == "" {
+		id, err := NewCartID()
+		return id, true, err
+	}
+	if cid, ok := ParseCartID(s); ok {
+		return cid, false, nil
+	}
+	// Legacy heuristic: if length == 16 and contains non-base62 chars, treat as legacy padded ID.
+	if len(s) == 16 && !isAllBase62(s) {
+		return FallbackFromString(strings.TrimRight(s, "\x00")), false, nil
+	}
+	return FallbackFromString(s), false, nil
+}
+
+// isAllBase62 returns true if every byte is in the base62 alphabet.
+func isAllBase62(s string) bool {
+	for i := 0; i < len(s); i++ {
+		if base62Rev[s[i]] == 0xFF {
+			return false
+		}
+	}
+	return true
+}
+
+// encodeBase62 turns a uint64 into base62 text.
+// Complexity: O(log_62 n) ~ at most 11 iterations for 64 bits.
+func encodeBase62(u uint64) string {
+	if u == 0 {
+		return "0"
+	}
+	// 62^11 = 743008370688 > 2^39; 62^11 > 2^64? Actually 62^11 ~= 5.18e19 < 2^64 (1.84e19)? 2^64 ≈ 1.84e19.
+	// 62^11 ≈ 5.18e19 > 2^64? Correction: 2^64 ≈ 1.844e19, so 62^11 > 2^64. Thus 11 chars suffice.
+	var buf [11]byte
+	i := len(buf)
+	for u > 0 {
+		i--
+		buf[i] = base62Alphabet[u%62]
+		u /= 62
+	}
+	return string(buf[i:])
+}
+
+// decodeBase62 converts a base62 string to uint64.
+// Returns (value, false) if any invalid character appears.
+func decodeBase62(s string) (uint64, bool) {
+	var v uint64
+	for i := 0; i < len(s); i++ {
+		c := s[i]
+		d := base62Rev[c]
+		if d == 0xFF {
+			return 0, false
+		}
+		v = v*62 + uint64(d)
+	}
+	return v, true
+}
+
+// ErrInvalidCartID can be returned by higher-level validation layers if you decide
+// to reject fallback-derived IDs (currently unused here).
+var ErrInvalidCartID = errors.New("invalid cart id")
+
+// ---------------------------------------------------------------------------
+// Legacy / Compatibility Conversion Helpers
+// ---------------------------------------------------------------------------
+
+// CartIDToLegacy converts a CartID (base62) into the legacy fixed-size CartId
+// ([16]byte) by copying the textual form (truncated or zero-padded).
+// NOTE: If the base62 string is longer than 16 (should not happen with current
+// 64-bit space), it will be truncated.
+func CartIDToLegacy(c CartID) CartId {
+	var id CartId
+	txt := c.String()
+	copy(id[:], []byte(txt))
+	return id
+}
+
+// LegacyToCartID upgrades a legacy CartId (padded) to a CartID by hashing its
+// trimmed string form (deterministic). This preserves stable mapping without
+// depending on original randomness.
+func LegacyToCartID(old CartId) CartID {
+	return UpgradeLegacyCartId(old)
+}
+
+// CartIDToKey returns the numeric key representation (uint64) for map indexing.
+func CartIDToKey(c CartID) uint64 {
+	return c.Raw()
+}
+
+// LegacyToCartKey converts a legacy CartId to the numeric key via deterministic
+// fallback hashing. (Uses the same logic as LegacyToCartID then returns raw.)
+func LegacyToCartKey(old CartId) uint64 {
+	return LegacyToCartID(old).Raw()
+}
+
+// ---------------------- Optional Helper Utilities ----------------------------
+
+// CartIDOrNew tries to parse s; if empty OR invalid returns a fresh ID.
+func CartIDOrNew(s string) (CartID, bool /*wasParsed*/, error) {
+	if cid, ok := ParseCartID(s); ok {
+		return cid, true, nil
+	}
+	id, err := NewCartID()
+	return id, false, err
+}
+
+// MustParseCartID panics if s is not a valid base62 ID (useful in tests).
+func MustParseCartID(s string) CartID {
+	if cid, ok := ParseCartID(s); ok {
+		return cid
+	}
+	panic(fmt.Sprintf("invalid CartID: %s", s))
+}
+
+// DebugString returns a verbose description (for logging / diagnostics).
+func (c CartID) DebugString() string {
+	return fmt.Sprintf("CartID(raw=%d txt=%s)", c.raw, c.String())
+}
+
+// Equal compares two CartIDs by raw value.
+func (c CartID) Equal(other CartID) bool {
+	return c.raw == other.raw
+}
+
+// CanonicalizeOrLegacy preserves legacy (non-base62) IDs without altering their
+// textual form, avoiding the previous behavior where fallback hashing replaced
+// the original string with a base62-encoded hash (which broke deterministic
+// key derivation across mixed call paths).
+//
+// Behavior:
+//   - s == ""      -> generate new CartID (generatedNew = true, wasBase62 = true)
+//   - base62 ok    -> return parsed CartID (generatedNew = false, wasBase62 = true)
+//   - otherwise    -> treat as legacy: raw = hash(s), txt = original s
+//
+// Returns:
+//
+//	cid          - CartID (txt preserved for legacy inputs)
+//	generatedNew - true only when a brand new ID was created due to empty input
+//	wasBase62    - true if the input was already canonical base62 (or generated)
+//	err          - only set if crypto/rand fails when generating a new ID
+func CanonicalizeOrLegacy(s string) (cid CartID, generatedNew bool, wasBase62 bool, err error) {
+	if s == "" {
+		id, e := NewCartID()
+		if e != nil {
+			return CartID{}, false, false, e
+		}
+		return id, true, true, nil
+	}
+	if parsed, ok := ParseCartID(s); ok {
+		return parsed, false, true, nil
+	}
+	// Legacy path: keep original text so downstream legacy-to-key hashing
+	// (which uses the visible string) yields consistent keys across code paths.
+	hashCID := FallbackFromString(s)
+	// Preserve original textual form
+	hashCID.txt = s
+	return hashCID, false, false, nil
+}

cart_id_test.go

@@ -0,0 +1,259 @@
+package main
+
+import (
+	"crypto/rand"
+	"encoding/binary"
+	"fmt"
+	mrand "math/rand"
+	"testing"
+)
+
+// TestEncodeDecodeBase62RoundTrip verifies encodeBase62/decodeBase62 are inverse.
+func TestEncodeDecodeBase62RoundTrip(t *testing.T) {
+	mrand.Seed(42)
+	for i := 0; i < 1000; i++ {
+		// Random 64-bit value
+		v := mrand.Uint64()
+		s := encodeBase62(v)
+		dec, ok := decodeBase62(s)
+		if !ok {
+			t.Fatalf("decodeBase62 failed for %d encoded=%s", v, s)
+		}
+		if dec != v {
+			t.Fatalf("round trip mismatch: have %d got %d (encoded=%s)", v, dec, s)
+		}
+	}
+	// Explicit zero test
+	if s := encodeBase62(0); s != "0" {
+		t.Fatalf("expected encodeBase62(0) == \"0\", got %q", s)
+	}
+	if v, ok := decodeBase62("0"); !ok || v != 0 {
+		t.Fatalf("decodeBase62(0) unexpected result v=%d ok=%v", v, ok)
+	}
+}
+
+// TestNewCartIDUniqueness generates a number of IDs and checks for duplicates.
+func TestNewCartIDUniqueness(t *testing.T) {
+	const n = 10000
+	seen := make(map[string]struct{}, n)
+	for i := 0; i < n; i++ {
+		id, err := NewCartID()
+		if err != nil {
+			t.Fatalf("NewCartID error: %v", err)
+		}
+		s := id.String()
+		if _, exists := seen[s]; exists {
+			t.Fatalf("duplicate CartID generated: %s", s)
+		}
+		seen[s] = struct{}{}
+		if id.IsZero() {
+			t.Fatalf("NewCartID returned zero value")
+		}
+	}
+}
+
+// TestParseCartIDValidation tests parsing of valid and invalid base62 strings.
+func TestParseCartIDValidation(t *testing.T) {
+	id, err := NewCartID()
+	if err != nil {
+		t.Fatalf("NewCartID error: %v", err)
+	}
+	parsed, ok := ParseCartID(id.String())
+	if !ok {
+		t.Fatalf("ParseCartID failed for valid id %s", id)
+	}
+	if parsed.raw != id.raw {
+		t.Fatalf("parsed raw mismatch: %d vs %d", parsed.raw, id.raw)
+	}
+
+	if _, ok := ParseCartID(""); ok {
+		t.Fatalf("expected empty string to be invalid")
+	}
+	// Invalid char ('-')
+	if _, ok := ParseCartID("abc-123"); ok {
+		t.Fatalf("expected invalid chars to fail parse")
+	}
+	// Overly long ( >16 )
+	if _, ok := ParseCartID("1234567890abcdefg"); ok {
+		t.Fatalf("expected overly long string to fail parse")
+	}
+}
+
+// TestFallbackDeterminism ensures fallback hashing is deterministic.
+func TestFallbackDeterminism(t *testing.T) {
+	inputs := []string{
+		"legacy-cart-1",
+		"legacy-cart-2",
+		"UPPER_lower_123",
+		"🚀unicode", // unicode bytes (will hash byte sequence)
+	}
+	for _, in := range inputs {
+		a := FallbackFromString(in)
+		b := FallbackFromString(in)
+		if a.raw != b.raw || a.String() != b.String() {
+			t.Fatalf("fallback mismatch for %q: %+v vs %+v", in, a, b)
+		}
+	}
+	// Distinct inputs should almost always differ; sample check
+	a := FallbackFromString("distinct-A")
+	b := FallbackFromString("distinct-B")
+	if a.raw == b.raw {
+		t.Fatalf("unexpected identical fallback hashes for distinct inputs")
+	}
+}
+
+// TestCanonicalizeIncomingBehavior covers main control flow branches.
+func TestCanonicalizeIncomingBehavior(t *testing.T) {
+	// Empty => new id
+	id1, generated, err := CanonicalizeIncoming("")
+	if err != nil || !generated || id1.IsZero() {
+		t.Fatalf("CanonicalizeIncoming empty failed: id=%v gen=%v err=%v", id1, generated, err)
+	}
+
+	// Valid base62 => parse; no generation
+	id2, gen2, err := CanonicalizeIncoming(id1.String())
+	if err != nil || gen2 || id2.raw != id1.raw {
+		t.Fatalf("CanonicalizeIncoming parse mismatch: id2=%v gen2=%v err=%v", id2, gen2, err)
+	}
+
+	// Legacy-like random containing invalid chars -> fallback
+	fallbackInput := "legacy\x00\x00padding"
+	id3, gen3, err := CanonicalizeIncoming(fallbackInput)
+	if err != nil || gen3 {
+		t.Fatalf("CanonicalizeIncoming fallback unexpected: id3=%v gen3=%v err=%v", id3, gen3, err)
+	}
+
+	// Deterministic fallback
+	id4, _, _ := CanonicalizeIncoming(fallbackInput)
+	if id3.raw != id4.raw {
+		t.Fatalf("fallback canonicalization not deterministic")
+	}
+}
+
+// TestUpgradeLegacyCartId ensures mapping of old CartId is stable.
+func TestUpgradeLegacyCartId(t *testing.T) {
+	var legacy CartId
+	copy(legacy[:], []byte("legacy-123456789")) // 15 bytes + padding
+	up1 := UpgradeLegacyCartId(legacy)
+	up2 := UpgradeLegacyCartId(legacy)
+	if up1.raw != up2.raw {
+		t.Fatalf("UpgradeLegacyCartId not deterministic: %v vs %v", up1, up2)
+	}
+	if up1.String() != up2.String() {
+		t.Fatalf("UpgradeLegacyCartId string mismatch: %s vs %s", up1, up2)
+	}
+}
+
+// BenchmarkNewCartID gives a rough idea of generation cost.
+func BenchmarkNewCartID(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		if _, err := NewCartID(); err != nil {
+			b.Fatalf("error: %v", err)
+		}
+	}
+}
+
+// BenchmarkEncodeBase62 measures encode speed in isolation.
+func BenchmarkEncodeBase62(b *testing.B) {
+	// Random sample of values
+	samples := make([]uint64, 1024)
+	for i := range samples {
+		var buf [8]byte
+		if _, err := rand.Read(buf[:]); err != nil {
+			b.Fatalf("rand: %v", err)
+		}
+		samples[i] = binary.BigEndian.Uint64(buf[:])
+	}
+	b.ResetTimer()
+	var sink string
+	for i := 0; i < b.N; i++ {
+		sink = encodeBase62(samples[i%len(samples)])
+	}
+	_ = sink
+}
+
+// BenchmarkDecodeBase62 measures decode speed.
+func BenchmarkDecodeBase62(b *testing.B) {
+	// Pre-encode
+	encoded := make([]string, 1024)
+	for i := range encoded {
+		encoded[i] = encodeBase62(uint64(i)<<32 | uint64(i))
+	}
+	b.ResetTimer()
+	var sum uint64
+	for i := 0; i < b.N; i++ {
+		v, ok := decodeBase62(encoded[i%len(encoded)])
+		if !ok {
+			b.Fatalf("decode failed")
+		}
+		sum ^= v
+	}
+	_ = sum
+}
+
+// TestLookupNDeterminism (ring integration smoke test) ensures LookupN
+// returns distinct hosts and stable ordering for a fixed ring.
+func TestLookupNDeterminism(t *testing.T) {
+	rb := NewRingBuilder().WithEpoch(1).WithVnodesPerHost(8).WithHosts([]string{"a", "b", "c"})
+	ring := rb.Build()
+	if ring.Empty() {
+		t.Fatalf("expected non-empty ring")
+	}
+	id := MustNewCartID()
+	owners1 := ring.LookupN(id.Raw(), 3)
+	owners2 := ring.LookupN(id.Raw(), 3)
+	if len(owners1) != len(owners2) {
+		t.Fatalf("LookupN length mismatch")
+	}
+	for i := range owners1 {
+		if owners1[i].Host != owners2[i].Host {
+			t.Fatalf("LookupN ordering instability at %d: %v vs %v", i, owners1[i], owners2[i])
+		}
+	}
+	// Distinct host constraint
+	seen := map[string]struct{}{}
+	for _, v := range owners1 {
+		if _, ok := seen[v.Host]; ok {
+			t.Fatalf("duplicate host in LookupN result: %v", owners1)
+		}
+		seen[v.Host] = struct{}{}
+	}
+}
+
+// TestRingFingerprintChanges ensures fingerprint updates with membership changes.
+func TestRingFingerprintChanges(t *testing.T) {
+	b1 := NewRingBuilder().WithEpoch(1).WithHosts([]string{"node1", "node2"})
+	r1 := b1.Build()
+	b2 := NewRingBuilder().WithEpoch(2).WithHosts([]string{"node1", "node2", "node3"})
+	r2 := b2.Build()
+	if r1.Fingerprint() == r2.Fingerprint() {
+		t.Fatalf("expected differing fingerprints after host set change")
+	}
+}
+
+// TestRingDiffHosts verifies added/removed host detection.
+func TestRingDiffHosts(t *testing.T) {
+	r1 := NewRingBuilder().WithEpoch(1).WithHosts([]string{"a", "b"}).Build()
+	r2 := NewRingBuilder().WithEpoch(2).WithHosts([]string{"b", "c"}).Build()
+	added, removed := r1.DiffHosts(r2)
+	if fmt.Sprintf("%v", added) != "[c]" {
+		t.Fatalf("expected added [c], got %v", added)
+	}
+	if fmt.Sprintf("%v", removed) != "[a]" {
+		t.Fatalf("expected removed [a], got %v", removed)
+	}
+}
+
+// TestRingLookupConsistency ensures direct Lookup and LookupID are aligned.
+func TestRingLookupConsistency(t *testing.T) {
+	ring := NewRingBuilder().WithEpoch(1).WithHosts([]string{"alpha", "beta"}).WithVnodesPerHost(4).Build()
+	id, _ := ParseCartID("1")
+	if id.IsZero() {
+		t.Fatalf("expected parsed id non-zero")
+	}
+	v1 := ring.Lookup(id.Raw())
+	v2 := ring.LookupID(id)
+	if v1.Host != v2.Host || v1.Hash != v2.Hash {
+		t.Fatalf("Lookup vs LookupID mismatch: %+v vs %+v", v1, v2)
+	}
+}

cart_state_mapper.go

@@ -0,0 +1,212 @@
+package main
+
+import (
+	messages "git.tornberg.me/go-cart-actor/proto"
+)
+
+// cart_state_mapper.go
+//
+// Utilities to translate between internal CartGrain state and the gRPC
+// (typed) protobuf representation CartState. This replaces the previous
+// JSON blob framing and enables type-safe replies over gRPC, as well as
+// internal reuse for HTTP handlers without an extra marshal / unmarshal
+// hop (you can marshal CartState directly for JSON responses if desired).
+//
+// Only the one‑way mapping (CartGrain -> CartState) is strictly required
+// for mutation / state replies. A reverse helper is included in case
+// future features (e.g. snapshot import, replay, or migration) need it.
+
+// ToCartState converts the in‑memory CartGrain into a protobuf CartState.
+func ToCartState(c *CartGrain) *messages.CartState {
+	if c == nil {
+		return nil
+	}
+
+	items := make([]*messages.CartItemState, 0, len(c.Items))
+	for _, it := range c.Items {
+		if it == nil {
+			continue
+		}
+		itemDiscountPerUnit := max(0, it.OrgPrice-it.Price)
+		itemTotalDiscount := itemDiscountPerUnit * int64(it.Quantity)
+
+		items = append(items, &messages.CartItemState{
+			Id:            int64(it.Id),
+			ItemId:        int64(it.ItemId),
+			Sku:           it.Sku,
+			Name:          it.Name,
+			Price:         it.Price,
+			Qty:           int32(it.Quantity),
+			TotalPrice:    it.TotalPrice,
+			TotalTax:      it.TotalTax,
+			OrgPrice:      it.OrgPrice,
+			TaxRate:       int32(it.TaxRate),
+			TotalDiscount: itemTotalDiscount,
+			Brand:         it.Brand,
+			Category:      it.Category,
+			Category2:     it.Category2,
+			Category3:     it.Category3,
+			Category4:     it.Category4,
+			Category5:     it.Category5,
+			Image:         it.Image,
+			Type:          it.ArticleType,
+			SellerId:      it.SellerId,
+			SellerName:    it.SellerName,
+			Disclaimer:    it.Disclaimer,
+			Outlet:        deref(it.Outlet),
+			StoreId:       deref(it.StoreId),
+			Stock:         int32(it.Stock),
+		})
+	}
+
+	deliveries := make([]*messages.DeliveryState, 0, len(c.Deliveries))
+	for _, d := range c.Deliveries {
+		if d == nil {
+			continue
+		}
+		itemIds := make([]int64, 0, len(d.Items))
+		for _, id := range d.Items {
+			itemIds = append(itemIds, int64(id))
+		}
+		var pp *messages.PickupPoint
+		if d.PickupPoint != nil {
+			// Copy to avoid accidental shared mutation (proto points are fine but explicit).
+			pp = &messages.PickupPoint{
+				Id:      d.PickupPoint.Id,
+				Name:    d.PickupPoint.Name,
+				Address: d.PickupPoint.Address,
+				City:    d.PickupPoint.City,
+				Zip:     d.PickupPoint.Zip,
+				Country: d.PickupPoint.Country,
+			}
+		}
+		deliveries = append(deliveries, &messages.DeliveryState{
+			Id:          int64(d.Id),
+			Provider:    d.Provider,
+			Price:       d.Price,
+			Items:       itemIds,
+			PickupPoint: pp,
+		})
+	}
+
+	return &messages.CartState{
+		Id:                c.Id.String(),
+		Items:             items,
+		TotalPrice:        c.TotalPrice,
+		TotalTax:          c.TotalTax,
+		TotalDiscount:     c.TotalDiscount,
+		Deliveries:        deliveries,
+		PaymentInProgress: c.PaymentInProgress,
+		OrderReference:    c.OrderReference,
+		PaymentStatus:     c.PaymentStatus,
+	}
+}
+
+// FromCartState merges a protobuf CartState into an existing CartGrain.
+// This is optional and primarily useful for snapshot import or testing.
+func FromCartState(cs *messages.CartState, g *CartGrain) *CartGrain {
+	if cs == nil {
+		return g
+	}
+	if g == nil {
+		g = &CartGrain{}
+	}
+	g.Id = ToCartId(cs.Id)
+	g.TotalPrice = cs.TotalPrice
+	g.TotalTax = cs.TotalTax
+	g.TotalDiscount = cs.TotalDiscount
+	g.PaymentInProgress = cs.PaymentInProgress
+	g.OrderReference = cs.OrderReference
+	g.PaymentStatus = cs.PaymentStatus
+
+	// Items
+	g.Items = g.Items[:0]
+	for _, it := range cs.Items {
+		if it == nil {
+			continue
+		}
+		outlet := toPtr(it.Outlet)
+		storeId := toPtr(it.StoreId)
+		g.Items = append(g.Items, &CartItem{
+			Id:          int(it.Id),
+			ItemId:      int(it.ItemId),
+			Sku:         it.Sku,
+			Name:        it.Name,
+			Price:       it.Price,
+			Quantity:    int(it.Qty),
+			TotalPrice:  it.TotalPrice,
+			TotalTax:    it.TotalTax,
+			OrgPrice:    it.OrgPrice,
+			TaxRate:     int(it.TaxRate),
+			Brand:       it.Brand,
+			Category:    it.Category,
+			Category2:   it.Category2,
+			Category3:   it.Category3,
+			Category4:   it.Category4,
+			Category5:   it.Category5,
+			Image:       it.Image,
+			ArticleType: it.Type,
+			SellerId:    it.SellerId,
+			SellerName:  it.SellerName,
+			Disclaimer:  it.Disclaimer,
+			Outlet:      outlet,
+			StoreId:     storeId,
+			Stock:       StockStatus(it.Stock),
+			// Tax, TaxRate already set via Price / Totals if needed
+		})
+		if it.Id > int64(g.lastItemId) {
+			g.lastItemId = int(it.Id)
+		}
+	}
+
+	// Deliveries
+	g.Deliveries = g.Deliveries[:0]
+	for _, d := range cs.Deliveries {
+		if d == nil {
+			continue
+		}
+
+		intIds := make([]int, 0, len(d.Items))
+		for _, id := range d.Items {
+			intIds = append(intIds, int(id))
+		}
+		var pp *messages.PickupPoint
+		if d.PickupPoint != nil {
+			pp = &messages.PickupPoint{
+				Id:      d.PickupPoint.Id,
+				Name:    d.PickupPoint.Name,
+				Address: d.PickupPoint.Address,
+				City:    d.PickupPoint.City,
+				Zip:     d.PickupPoint.Zip,
+				Country: d.PickupPoint.Country,
+			}
+		}
+		g.Deliveries = append(g.Deliveries, &CartDelivery{
+			Id:          int(d.Id),
+			Provider:    d.Provider,
+			Price:       d.Price,
+			Items:       intIds,
+			PickupPoint: pp,
+		})
+		if d.Id > int64(g.lastDeliveryId) {
+			g.lastDeliveryId = int(d.Id)
+		}
+	}
+
+	return g
+}
+
+// Helper to safely de-reference optional string pointers to value or "".
+func deref(p *string) string {
+	if p == nil {
+		return ""
+	}
+	return *p
+}
+
+func toPtr(s string) *string {
+	if s == "" {
+		return nil
+	}
+	return &s
+}

checkout_builder.go

@@ -0,0 +1,119 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+)
+
+// CheckoutMeta carries the external / URL metadata required to build a
+// Klarna CheckoutOrder from a CartGrain snapshot. It deliberately excludes
+// any Klarna-specific response fields (HTML snippet, client token, etc.).
+type CheckoutMeta struct {
+	Terms        string
+	Checkout     string
+	Confirmation string
+	Validation   string
+	Push         string
+	Country      string
+	Currency     string // optional override (defaults to "SEK" if empty)
+	Locale       string // optional override (defaults to "sv-se" if empty)
+}
+
+// BuildCheckoutOrderPayload converts the current cart grain + meta information
+// into a CheckoutOrder domain struct and returns its JSON-serialized payload
+// (to send to Klarna) alongside the structured CheckoutOrder object.
+//
+// This function is PURE: it does not perform any network I/O or mutate the
+// grain. The caller is responsible for:
+//
+//  1. Choosing whether to create or update the Klarna order.
+//  2. Invoking KlarnaClient.CreateOrder / UpdateOrder with the returned payload.
+//  3. Applying an InitializeCheckout mutation (or equivalent) with the
+//     resulting Klarna order id + status.
+//
+// If you later need to support different tax rates per line, you can extend
+// CartItem / Delivery to expose that data and propagate it here.
+func BuildCheckoutOrderPayload(grain *CartGrain, meta *CheckoutMeta) ([]byte, *CheckoutOrder, error) {
+	if grain == nil {
+		return nil, nil, fmt.Errorf("nil grain")
+	}
+	if meta == nil {
+		return nil, nil, fmt.Errorf("nil checkout meta")
+	}
+
+	currency := meta.Currency
+	if currency == "" {
+		currency = "SEK"
+	}
+	locale := meta.Locale
+	if locale == "" {
+		locale = "sv-se"
+	}
+	country := meta.Country
+	if country == "" {
+		country = "SE" // sensible default; adjust if multi-country support changes
+	}
+
+	lines := make([]*Line, 0, len(grain.Items)+len(grain.Deliveries))
+
+	// Item lines
+	for _, it := range grain.Items {
+		if it == nil {
+			continue
+		}
+		lines = append(lines, &Line{
+			Type:           "physical",
+			Reference:      it.Sku,
+			Name:           it.Name,
+			Quantity:       it.Quantity,
+			UnitPrice:      int(it.Price),
+			TaxRate:        2500, // TODO: derive if variable tax rates are introduced
+			QuantityUnit:   "st",
+			TotalAmount:    int(it.TotalPrice),
+			TotalTaxAmount: int(it.TotalTax),
+			ImageURL:       fmt.Sprintf("https://www.elgiganten.se%s", it.Image),
+		})
+	}
+
+	// Delivery lines
+	for _, d := range grain.Deliveries {
+		if d == nil || d.Price <= 0 {
+			continue
+		}
+		lines = append(lines, &Line{
+			Type:           "shipping_fee",
+			Reference:      d.Provider,
+			Name:           "Delivery",
+			Quantity:       1,
+			UnitPrice:      int(d.Price),
+			TaxRate:        2500,
+			QuantityUnit:   "st",
+			TotalAmount:    int(d.Price),
+			TotalTaxAmount: int(GetTaxAmount(d.Price, 2500)),
+		})
+	}
+
+	order := &CheckoutOrder{
+		PurchaseCountry:    country,
+		PurchaseCurrency:   currency,
+		Locale:             locale,
+		OrderAmount:        int(grain.TotalPrice),
+		OrderTaxAmount:     int(grain.TotalTax),
+		OrderLines:         lines,
+		MerchantReference1: grain.Id.String(),
+		MerchantURLS: &CheckoutMerchantURLS{
+			Terms:        meta.Terms,
+			Checkout:     meta.Checkout,
+			Confirmation: meta.Confirmation,
+			Validation:   meta.Validation,
+			Push:         meta.Push,
+		},
+	}
+
+	payload, err := json.Marshal(order)
+	if err != nil {
+		return nil, nil, fmt.Errorf("marshal checkout order: %w", err)
+	}
+
+	return payload, order, nil
+}

cookies.txt

@@ -0,0 +1,5 @@
+# Netscape HTTP Cookie File
+# https://curl.se/docs/http-cookies.html
+# This file was generated by libcurl! Edit at your own risk.
+
+#HttpOnly_localhost	FALSE	/	FALSE	1761304670	cartid	4393545184291837

deployment/deployment-no.yaml

@@ -1,276 +0,0 @@
-apiVersion: v1
-kind: Secret
-metadata:
-  name:  klarna-api-credentials
-data:
-  username: ZjQzZDY3YjEtNzA2Yy00NTk2LTliNTgtYjg1YjU2NDEwZTUw
-  password: a2xhcm5hX3Rlc3RfYXBpX0trUWhWVE5yYVZsV2FsTnhTRVp3Y1ZSSFF5UkVNRmxyY25Kd1AxSndQMGdzWmpRelpEWTNZakV0TnpBMll5MDBOVGsyTFRsaU5UZ3RZamcxWWpVMk5ERXdaVFV3TERFc2JUUkNjRFpWU1RsTllsSk1aMlEyVEc4MmRVODNZMkozUlRaaFdEZDViV3AwYkhGV1JqTjVNQzlaYXow
-type: Opaque
----
-apiVersion: apps/v1
-kind: Deployment
-metadata:
-  labels:
-    app: cart-actor
-    arch: amd64
-  name: cart-actor-x86
-spec:
-  replicas: 0
-  selector:
-    matchLabels:
-      app: cart-actor
-      arch: amd64
-  template:
-    metadata:
-      labels:
-        app: cart-actor
-        actor-pool: cart
-        arch: amd64
-    spec:
-      affinity:
-        nodeAffinity:
-          requiredDuringSchedulingIgnoredDuringExecution:
-            nodeSelectorTerms:
-              - matchExpressions:
-                - key: kubernetes.io/arch
-                  operator: NotIn
-                  values:
-                    - arm64
-      volumes:
-        - name: data
-          nfs:
-            path: /i-data/7a8af061/nfs/cart-actor-no
-            server: 10.10.1.10
-      imagePullSecrets:
-        - name: regcred
-      serviceAccountName: default
-      containers:
-        - image: registry.knatofs.se/go-cart-actor-amd64:latest
-          name: cart-actor-amd64
-          imagePullPolicy: Always
-          lifecycle:
-            preStop:
-              exec:
-                command: ["sleep", "15"]
-          ports:
-            - containerPort: 8080
-              name: web
-            - containerPort: 1234
-              name: echo
-            - containerPort: 1337
-              name: rpc
-            - containerPort: 1338
-              name: quorum
-          livenessProbe:
-            httpGet:
-              path: /livez
-              port: web
-            failureThreshold: 1
-            periodSeconds: 10
-          readinessProbe:
-            httpGet:
-              path: /readyz
-              port: web
-            failureThreshold: 2
-            initialDelaySeconds: 2
-            periodSeconds: 10
-          volumeMounts:
-            - mountPath: "/data"
-              name: data
-          resources:
-            limits:
-              memory: "768Mi"
-            requests:
-              memory: "70Mi"
-              cpu: "1200m"
-          env:
-            - name: TZ
-              value: "Europe/Stockholm"
-            - name: KLARNA_API_USERNAME
-              valueFrom:
-                secretKeyRef:
-                  name: klarna-api-credentials
-                  key: username
-            - name: KLARNA_API_PASSWORD
-              valueFrom:
-                secretKeyRef:
-                  name: klarna-api-credentials
-                  key: password
-            - name: POD_IP
-              valueFrom:
-                fieldRef:
-                  fieldPath: status.podIP
-            - name: AMQP_URL
-              value: "amqp://admin:12bananer@rabbitmq.dev:5672/"
-            - name: BASE_URL
-              value: "https://s10n-no.tornberg.me"
-            - name: CART_BASE_URL
-              value: "https://cart-no.tornberg.me"
-            - name: POD_NAME
-              valueFrom:
-                fieldRef:
-                  fieldPath: metadata.name
----
-apiVersion: apps/v1
-kind: Deployment
-metadata:
-  labels:
-    app: cart-actor
-    arch: arm64
-  name: cart-actor-arm64
-spec:
-  replicas: 3
-  selector:
-    matchLabels:
-      app: cart-actor
-      arch: arm64
-  template:
-    metadata:
-      labels:
-        app: cart-actor
-        actor-pool: cart
-        arch: arm64
-    spec:
-      affinity:
-        nodeAffinity:
-          requiredDuringSchedulingIgnoredDuringExecution:
-            nodeSelectorTerms:
-              - matchExpressions:
-                - key: kubernetes.io/hostname
-                  operator: NotIn
-                  values:
-                    - masterpi
-                - key: kubernetes.io/arch
-                  operator: In
-                  values:
-                    - arm64
-      volumes:
-        - name: data
-          nfs:
-            path: /i-data/7a8af061/nfs/cart-actor-no
-            server: 10.10.1.10
-      imagePullSecrets:
-        - name: regcred
-      serviceAccountName: default
-      containers:
-        - image: registry.knatofs.se/go-cart-actor:latest
-          name: cart-actor-arm64
-          imagePullPolicy: Always
-          lifecycle:
-            preStop:
-              exec:
-                command: ["sleep", "15"]
-          ports:
-            - containerPort: 8080
-              name: web
-            - containerPort: 1234
-              name: echo
-            - containerPort: 1337
-              name: rpc
-            - containerPort: 1338
-              name: quorum
-          livenessProbe:
-            httpGet:
-              path: /livez
-              port: web
-            failureThreshold: 1
-            periodSeconds: 10
-          readinessProbe:
-            httpGet:
-              path: /readyz
-              port: web
-            failureThreshold: 2
-            initialDelaySeconds: 2
-            periodSeconds: 10
-          volumeMounts:
-            - mountPath: "/data"
-              name: data
-          resources:
-            limits:
-              memory: "768Mi"
-            requests:
-              memory: "70Mi"
-              cpu: "1200m"
-          env:
-            - name: TZ
-              value: "Europe/Stockholm"
-            - name: KLARNA_API_USERNAME
-              valueFrom:
-                secretKeyRef:
-                  name: klarna-api-credentials
-                  key: username
-            - name: KLARNA_API_PASSWORD
-              valueFrom:
-                secretKeyRef:
-                  name: klarna-api-credentials
-                  key: password
-            - name: POD_IP
-              valueFrom:
-                fieldRef:
-                  fieldPath: status.podIP
-            - name: AMQP_URL
-              value: "amqp://admin:12bananer@rabbitmq.dev:5672/"
-            - name: BASE_URL
-              value: "https://s10n-no.tornberg.me"
-            - name: CART_BASE_URL
-              value: "https://cart-no.tornberg.me"
-            - name: POD_NAME
-              valueFrom:
-                fieldRef:
-                  fieldPath: metadata.name
----
-kind: Service
-apiVersion: v1
-metadata:
-  name: cart-echo
-spec:
-  selector:
-    app: cart-actor
-  type: LoadBalancer
-  ports:
-    - name: echo
-      port: 1234
----
-kind: Service
-apiVersion: v1
-metadata:
-  name: cart-actor
-  annotations:
-    prometheus.io/port: "8080"
-    prometheus.io/scrape: "true"
-    prometheus.io/path: "/metrics"
-spec:
-  selector:
-    app: cart-actor
-  ports:
-    - name: web
-      port: 8080
----
-apiVersion: networking.k8s.io/v1
-kind: Ingress
-metadata:
-  name: cart-ingress
-  annotations:
-    cert-manager.io/cluster-issuer: letsencrypt-prod
-    # nginx.ingress.kubernetes.io/affinity: "cookie"
-    # nginx.ingress.kubernetes.io/session-cookie-name: "cart-affinity"
-    # nginx.ingress.kubernetes.io/session-cookie-expires: "172800"
-    # nginx.ingress.kubernetes.io/session-cookie-max-age: "172800"
-    nginx.ingress.kubernetes.io/proxy-body-size: 4m
-spec:
-  ingressClassName: nginx
-  tls:
-    - hosts:
-        - cart-no.tornberg.me
-      secretName: cart-actor-no-tls-secret
-  rules:
-    - host: cart-no.tornberg.me
-      http:
-        paths:
-          - path: /
-            pathType: Prefix
-            backend:
-              service:
-                name: cart-actor
-                port:
-                  number: 8080

deployment/deployment.yaml

@@ -1,272 +1,252 @@
 apiVersion: v1
 kind: Secret
 metadata:
-  name:  klarna-api-credentials
+    name: klarna-api-credentials
 data:
-  username: ZjQzZDY3YjEtNzA2Yy00NTk2LTliNTgtYjg1YjU2NDEwZTUw
+    username: ZjQzZDY3YjEtNzA2Yy00NTk2LTliNTgtYjg1YjU2NDEwZTUw
-  password: a2xhcm5hX3Rlc3RfYXBpX0trUWhWVE5yYVZsV2FsTnhTRVp3Y1ZSSFF5UkVNRmxyY25Kd1AxSndQMGdzWmpRelpEWTNZakV0TnpBMll5MDBOVGsyTFRsaU5UZ3RZamcxWWpVMk5ERXdaVFV3TERFc2JUUkNjRFpWU1RsTllsSk1aMlEyVEc4MmRVODNZMkozUlRaaFdEZDViV3AwYkhGV1JqTjVNQzlaYXow
+    password: a2xhcm5hX3Rlc3RfYXBpX0trUWhWVE5yYVZsV2FsTnhTRVp3Y1ZSSFF5UkVNRmxyY25Kd1AxSndQMGdzWmpRelpEWTNZakV0TnpBMll5MDBOVGsyTFRsaU5UZ3RZamcxWWpVMk5ERXdaVFV3TERFc2JUUkNjRFpWU1RsTllsSk1aMlEyVEc4MmRVODNZMkozUlRaaFdEZDViV3AwYkhGV1JqTjVNQzlaYXow
 type: Opaque
 ---
 apiVersion: apps/v1
 kind: Deployment
 metadata:
-  labels:
+    labels:
-    app: cart-actor
-    arch: amd64
-  name: cart-actor-x86
-spec:
-  replicas: 0
-  selector:
-    matchLabels:
-      app: cart-actor
-      arch: amd64
-  template:
-    metadata:
-      labels:
         app: cart-actor
-        actor-pool: cart
         arch: amd64
-    spec:
+    name: cart-actor-x86
-      affinity:
+spec:
-        nodeAffinity:
+    replicas: 0
-          requiredDuringSchedulingIgnoredDuringExecution:
+    selector:
-            nodeSelectorTerms:
+        matchLabels:
-              - matchExpressions:
+            app: cart-actor
-                - key: kubernetes.io/arch
+            arch: amd64
-                  operator: NotIn
+    template:
-                  values:
+        metadata:
-                    - arm64
+            labels:
-      volumes:
+                app: cart-actor
-        - name: data
+                actor-pool: cart
-          nfs:
+                arch: amd64
-            path: /i-data/7a8af061/nfs/cart-actor
+        spec:
-            server: 10.10.1.10
+            affinity:
-      imagePullSecrets:
+                nodeAffinity:
-        - name: regcred
+                    requiredDuringSchedulingIgnoredDuringExecution:
-      serviceAccountName: default
+                        nodeSelectorTerms:
-      containers:
+                            - matchExpressions:
-        - image: registry.knatofs.se/go-cart-actor-amd64:latest
+                                  - key: kubernetes.io/arch
-          name: cart-actor-amd64
+                                    operator: NotIn
-          imagePullPolicy: Always
+                                    values:
-          lifecycle:
+                                        - arm64
-            preStop:
+            volumes:
-              exec:
+                - name: data
-                command: ["sleep", "15"]
+                  nfs:
-          ports:
+                      path: /i-data/7a8af061/nfs/cart-actor
-            - containerPort: 8080
+                      server: 10.10.1.10
-              name: web
+            imagePullSecrets:
-            - containerPort: 1234
+                - name: regcred
-              name: echo
+            serviceAccountName: default
-            - containerPort: 1337
+            containers:
-              name: rpc
+                - image: registry.knatofs.se/go-cart-actor-amd64:latest
-            - containerPort: 1338
+                  name: cart-actor-amd64
-              name: quorum
+                  imagePullPolicy: Always
-          livenessProbe:
+                  lifecycle:
-            httpGet:
+                      preStop:
-              path: /livez
+                          exec:
-              port: web
+                              command: ["sleep", "15"]
-            failureThreshold: 1
+                  ports:
-            periodSeconds: 10
+                      - containerPort: 8080
-          readinessProbe:
+                        name: web
-            httpGet:
+                      - containerPort: 1337
-              path: /readyz
+                        name: rpc
-              port: web
+                  livenessProbe:
-            failureThreshold: 2
+                      httpGet:
-            initialDelaySeconds: 2
+                          path: /livez
-            periodSeconds: 10
+                          port: web
-          volumeMounts:
+                      failureThreshold: 1
-            - mountPath: "/data"
+                      periodSeconds: 10
-              name: data
+                  readinessProbe:
-          resources:
+                      httpGet:
-            limits:
+                          path: /readyz
-              memory: "768Mi"
+                          port: web
-            requests:
+                      failureThreshold: 2
-              memory: "70Mi"
+                      initialDelaySeconds: 2
-              cpu: "1200m"
+                      periodSeconds: 10
-          env:
+                  volumeMounts:
-            - name: TZ
+                      - mountPath: "/data"
-              value: "Europe/Stockholm"
+                        name: data
-            - name: KLARNA_API_USERNAME
+                  resources:
-              valueFrom:
+                      limits:
-                secretKeyRef:
+                          memory: "768Mi"
-                  name: klarna-api-credentials
+                      requests:
-                  key: username
+                          memory: "70Mi"
-            - name: KLARNA_API_PASSWORD
+                          cpu: "1200m"
-              valueFrom:
+                  env:
-                secretKeyRef:
+                      - name: TZ
-                  name: klarna-api-credentials
+                        value: "Europe/Stockholm"
-                  key: password
+                      - name: KLARNA_API_USERNAME
-            - name: POD_IP
+                        valueFrom:
-              valueFrom:
+                            secretKeyRef:
-                fieldRef:
+                                name: klarna-api-credentials
-                  fieldPath: status.podIP
+                                key: username
-            - name: AMQP_URL
+                      - name: KLARNA_API_PASSWORD
-              value: "amqp://admin:12bananer@rabbitmq.dev:5672/"
+                        valueFrom:
-            # - name: BASE_URL
+                            secretKeyRef:
-            #   value: "https://s10n-no.tornberg.me"
+                                name: klarna-api-credentials
-            - name: POD_NAME
+                                key: password
-              valueFrom:
+                      - name: POD_IP
-                fieldRef:
+                        valueFrom:
-                  fieldPath: metadata.name
+                            fieldRef:
+                                fieldPath: status.podIP
+                      - name: AMQP_URL
+                        value: "amqp://admin:12bananer@rabbitmq.dev:5672/"
+                      # - name: BASE_URL
+                      #   value: "https://s10n-no.tornberg.me"
+                      - name: POD_NAME
+                        valueFrom:
+                            fieldRef:
+                                fieldPath: metadata.name
 ---
 apiVersion: apps/v1
 kind: Deployment
 metadata:
-  labels:
+    labels:
-    app: cart-actor
-    arch: arm64
-  name: cart-actor-arm64
-spec:
-  replicas: 0
-  selector:
-    matchLabels:
-      app: cart-actor
-      arch: arm64
-  template:
-    metadata:
-      labels:
         app: cart-actor
-        actor-pool: cart
         arch: arm64
-    spec:
+    name: cart-actor-arm64
-      affinity:
+spec:
-        nodeAffinity:
+    replicas: 3
-          requiredDuringSchedulingIgnoredDuringExecution:
+    selector:
-            nodeSelectorTerms:
+        matchLabels:
-              - matchExpressions:
+            app: cart-actor
-                - key: kubernetes.io/hostname
+            arch: arm64
-                  operator: NotIn
+    template:
-                  values:
+        metadata:
-                    - masterpi
+            labels:
-                - key: kubernetes.io/arch
+                app: cart-actor
-                  operator: In
+                actor-pool: cart
-                  values:
+                arch: arm64
-                    - arm64
+        spec:
-      volumes:
+            affinity:
-        - name: data
+                nodeAffinity:
-          nfs:
+                    requiredDuringSchedulingIgnoredDuringExecution:
-            path: /i-data/7a8af061/nfs/cart-actor
+                        nodeSelectorTerms:
-            server: 10.10.1.10
+                            - matchExpressions:
-      imagePullSecrets:
+                                  - key: kubernetes.io/hostname
-        - name: regcred
+                                    operator: NotIn
-      serviceAccountName: default
+                                    values:
-      containers:
+                                        - masterpi
-        - image: registry.knatofs.se/go-cart-actor:latest
+                                  - key: kubernetes.io/arch
-          name: cart-actor-arm64
+                                    operator: In
-          imagePullPolicy: Always
+                                    values:
-          lifecycle:
+                                        - arm64
-            preStop:
+            volumes:
-              exec:
+                - name: data
-                command: ["sleep", "15"]
+                  nfs:
-          ports:
+                      path: /i-data/7a8af061/nfs/cart-actor
-            - containerPort: 8080
+                      server: 10.10.1.10
-              name: web
+            imagePullSecrets:
-            - containerPort: 1234
+                - name: regcred
-              name: echo
+            serviceAccountName: default
-            - containerPort: 1337
+            containers:
-              name: rpc
+                - image: registry.knatofs.se/go-cart-actor:latest
-            - containerPort: 1338
+                  name: cart-actor-arm64
-              name: quorum
+                  imagePullPolicy: Always
-          livenessProbe:
+                  lifecycle:
-            httpGet:
+                      preStop:
-              path: /livez
+                          exec:
-              port: web
+                              command: ["sleep", "15"]
-            failureThreshold: 1
+                  ports:
-            periodSeconds: 10
+                      - containerPort: 8080
-          readinessProbe:
+                        name: web
-            httpGet:
+                      - containerPort: 1337
-              path: /readyz
+                        name: rpc
-              port: web
+                  livenessProbe:
-            failureThreshold: 2
+                      httpGet:
-            initialDelaySeconds: 2
+                          path: /livez
-            periodSeconds: 10
+                          port: web
-          volumeMounts:
+                      failureThreshold: 1
-            - mountPath: "/data"
+                      periodSeconds: 10
-              name: data
+                  readinessProbe:
-          resources:
+                      httpGet:
-            limits:
+                          path: /readyz
-              memory: "768Mi"
+                          port: web
-            requests:
+                      failureThreshold: 2
-              memory: "70Mi"
+                      initialDelaySeconds: 2
-              cpu: "1200m"
+                      periodSeconds: 10
-          env:
+                  volumeMounts:
-            - name: TZ
+                      - mountPath: "/data"
-              value: "Europe/Stockholm"
+                        name: data
-            - name: KLARNA_API_USERNAME
+                  resources:
-              valueFrom:
+                      limits:
-                secretKeyRef:
+                          memory: "768Mi"
-                  name: klarna-api-credentials
+                      requests:
-                  key: username
+                          memory: "70Mi"
-            - name: KLARNA_API_PASSWORD
+                          cpu: "1200m"
-              valueFrom:
+                  env:
-                secretKeyRef:
+                      - name: TZ
-                  name: klarna-api-credentials
+                        value: "Europe/Stockholm"
-                  key: password
+                      - name: KLARNA_API_USERNAME
-            - name: POD_IP
+                        valueFrom:
-              valueFrom:
+                            secretKeyRef:
-                fieldRef:
+                                name: klarna-api-credentials
-                  fieldPath: status.podIP
+                                key: username
-            - name: AMQP_URL
+                      - name: KLARNA_API_PASSWORD
-              value: "amqp://admin:12bananer@rabbitmq.dev:5672/"
+                        valueFrom:
-            # - name: BASE_URL
+                            secretKeyRef:
-            #   value: "https://s10n-no.tornberg.me"
+                                name: klarna-api-credentials
-            - name: POD_NAME
+                                key: password
-              valueFrom:
+                      - name: POD_IP
-                fieldRef:
+                        valueFrom:
-                  fieldPath: metadata.name
+                            fieldRef:
+                                fieldPath: status.podIP
+                      - name: AMQP_URL
+                        value: "amqp://admin:12bananer@rabbitmq.dev:5672/"
+                      # - name: BASE_URL
+                      #   value: "https://s10n-no.tornberg.me"
+                      - name: POD_NAME
+                        valueFrom:
+                            fieldRef:
+                                fieldPath: metadata.name
 ---
 kind: Service
 apiVersion: v1
 metadata:
-  name: cart-echo
+    name: cart-actor
+    annotations:
+        prometheus.io/port: "8080"
+        prometheus.io/scrape: "true"
+        prometheus.io/path: "/metrics"
 spec:
-  selector:
+    selector:
-    app: cart-actor
+        app: cart-actor
-  type: LoadBalancer
+    ports:
-  ports:
+        - name: web
-    - name: echo
+          port: 8080
-      port: 1234
----
-kind: Service
-apiVersion: v1
-metadata:
-  name: cart-actor
-  annotations:
-    prometheus.io/port: "8080"
-    prometheus.io/scrape: "true"
-    prometheus.io/path: "/metrics"
-spec:
-  selector:
-    app: cart-actor
-  ports:
-    - name: web
-      port: 8080
 ---
 apiVersion: networking.k8s.io/v1
 kind: Ingress
 metadata:
-  name: cart-ingress
+    name: cart-ingress
-  annotations:
+    annotations:
-    cert-manager.io/cluster-issuer: letsencrypt-prod
+        cert-manager.io/cluster-issuer: letsencrypt-prod
-    # nginx.ingress.kubernetes.io/affinity: "cookie"
+        # nginx.ingress.kubernetes.io/affinity: "cookie"
-    # nginx.ingress.kubernetes.io/session-cookie-name: "cart-affinity"
+        # nginx.ingress.kubernetes.io/session-cookie-name: "cart-affinity"
-    # nginx.ingress.kubernetes.io/session-cookie-expires: "172800"
+        # nginx.ingress.kubernetes.io/session-cookie-expires: "172800"
-    # nginx.ingress.kubernetes.io/session-cookie-max-age: "172800"
+        # nginx.ingress.kubernetes.io/session-cookie-max-age: "172800"
-    nginx.ingress.kubernetes.io/proxy-body-size: 4m
+        nginx.ingress.kubernetes.io/proxy-body-size: 4m
 spec:
-  ingressClassName: nginx
+    ingressClassName: nginx
-  tls:
+    tls:
-    - hosts:
+        - hosts:
-        - cart.tornberg.me
+              - cart.tornberg.me
-      secretName: cart-actor-tls-secret
+          secretName: cart-actor-tls-secret
-  rules:
+    rules:
-    - host: cart.tornberg.me
+        - host: cart.tornberg.me
-      http:
+          http:
-        paths:
+              paths:
-          - path: /
+                  - path: /
-            pathType: Prefix
+                    pathType: Prefix
-            backend:
+                    backend:
-              service:
+                        service:
-                name: cart-actor
+                            name: cart-actor
-                port:
+                            port:
-                  number: 8080
+                                number: 8080

deployment/scaling.yaml

@@ -1,25 +1,101 @@
-apiVersion: autoscaling/v1
+apiVersion: autoscaling/v2
 kind: HorizontalPodAutoscaler
 metadata:
-  name: cart-scaler-amd
+    name: cart-scaler-amd
 spec:
-  scaleTargetRef:
+    scaleTargetRef:
-    apiVersion: apps/v1
+        apiVersion: apps/v1
-    kind: Deployment
+        kind: Deployment
-    name: cart-actor-x86
+        name: cart-actor-x86
-  minReplicas: 3
+    minReplicas: 3
-  maxReplicas: 9
+    maxReplicas: 9
-  targetCPUUtilizationPercentage: 30
+    behavior:
+        scaleUp:
+            stabilizationWindowSeconds: 60
+            policies:
+                - type: Percent
+                  value: 100
+                  periodSeconds: 60
+        scaleDown:
+            stabilizationWindowSeconds: 180
+            policies:
+                - type: Percent
+                  value: 50
+                  periodSeconds: 60
+    metrics:
+        - type: Resource
+          resource:
+              name: cpu
+              target:
+                  type: Utilization
+                  averageUtilization: 50
+        # Future custom metric (example):
+        # - type: Pods
+        #   pods:
+        #     metric:
+        #       name: cart_mutations_per_second
+        #     target:
+        #       type: AverageValue
+        #       averageValue: "15"
+        # - type: Object
+        #   object:
+        #     describedObject:
+        #       apiVersion: networking.k8s.io/v1
+        #       kind: Ingress
+        #       name: cart-ingress
+        #     metric:
+        #       name: http_requests_per_second
+        #     target:
+        #       type: Value
+        #       value: "100"
 ---
-apiVersion: autoscaling/v1
+apiVersion: autoscaling/v2
 kind: HorizontalPodAutoscaler
 metadata:
-  name: cart-scaler-arm
+    name: cart-scaler-arm
 spec:
-  scaleTargetRef:
+    scaleTargetRef:
-    apiVersion: apps/v1
+        apiVersion: apps/v1
-    kind: Deployment
+        kind: Deployment
-    name: cart-actor-arm64
+        name: cart-actor-arm64
-  minReplicas: 3
+    minReplicas: 3
-  maxReplicas: 9
+    maxReplicas: 9
-  targetCPUUtilizationPercentage: 30
+    behavior:
+        scaleUp:
+            stabilizationWindowSeconds: 60
+            policies:
+                - type: Percent
+                  value: 100
+                  periodSeconds: 60
+        scaleDown:
+            stabilizationWindowSeconds: 180
+            policies:
+                - type: Percent
+                  value: 50
+                  periodSeconds: 60
+    metrics:
+        - type: Resource
+          resource:
+              name: cpu
+              target:
+                  type: Utilization
+                  averageUtilization: 50
+        # Future custom metric (example):
+        # - type: Pods
+        #   pods:
+        #     metric:
+        #       name: cart_mutations_per_second
+        #     target:
+        #       type: AverageValue
+        #       averageValue: "15"
+        # - type: Object
+        #   object:
+        #     describedObject:
+        #       apiVersion: networking.k8s.io/v1
+        #       kind: Ingress
+        #       name: cart-ingress
+        #     metric:
+        #       name: http_requests_per_second
+        #     target:
+        #       type: Value
+        #       value: "100"

discovery.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"context"
+	"sync"
 
 	v1 "k8s.io/api/core/v1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
@@ -75,3 +76,97 @@ func NewK8sDiscovery(client *kubernetes.Clientset) *K8sDiscovery {
 		client: client,
 	}
 }
+
+// MockDiscovery is an in-memory Discovery implementation for tests.
+// It allows deterministic injection of host additions/removals without
+// depending on Kubernetes API machinery.
+type MockDiscovery struct {
+	mu      sync.RWMutex
+	hosts   []string
+	events  chan HostChange
+	closed  bool
+	started bool
+}
+
+// NewMockDiscovery creates a mock discovery with an initial host list.
+func NewMockDiscovery(initial []string) *MockDiscovery {
+	cp := make([]string, len(initial))
+	copy(cp, initial)
+	return &MockDiscovery{
+		hosts:  cp,
+		events: make(chan HostChange, 32),
+	}
+}
+
+// Discover returns the current host snapshot.
+func (m *MockDiscovery) Discover() ([]string, error) {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+	cp := make([]string, len(m.hosts))
+	copy(cp, m.hosts)
+	return cp, nil
+}
+
+// Watch returns a channel that will receive HostChange events.
+// The channel is buffered; AddHost/RemoveHost push events non-blockingly.
+func (m *MockDiscovery) Watch() (<-chan HostChange, error) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	if m.closed {
+		return nil, context.Canceled
+	}
+	m.started = true
+	return m.events, nil
+}
+
+// AddHost inserts a new host (if absent) and emits an Added event.
+func (m *MockDiscovery) AddHost(host string) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	if m.closed {
+		return
+	}
+	for _, h := range m.hosts {
+		if h == host {
+			return
+		}
+	}
+	m.hosts = append(m.hosts, host)
+	if m.started {
+		m.events <- HostChange{Host: host, Type: watch.Added}
+	}
+}
+
+// RemoveHost removes a host (if present) and emits a Deleted event.
+func (m *MockDiscovery) RemoveHost(host string) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	if m.closed {
+		return
+	}
+	idx := -1
+	for i, h := range m.hosts {
+		if h == host {
+			idx = i
+			break
+		}
+	}
+	if idx == -1 {
+		return
+	}
+	m.hosts = append(m.hosts[:idx], m.hosts[idx+1:]...)
+	if m.started {
+		m.events <- HostChange{Host: host, Type: watch.Deleted}
+	}
+}
+
+// Close closes the event channel (idempotent).
+func (m *MockDiscovery) Close() {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	if m.closed {
+		return
+	}
+	m.closed = true
+	close(m.events)
+}

disk-storage.go

@@ -3,7 +3,6 @@ package main
 import (
 	"encoding/gob"
 	"fmt"
-	"log"
 	"os"
 	"time"
 )
@@ -23,59 +22,18 @@ func NewDiskStorage(stateFile string) (*DiskStorage, error) {
 	return ret, err
 }
 
-func saveMessages(messages []StorableMessage, id CartId) error {
+func saveMessages(_ interface{}, _ CartId) error {
-
+	// No-op: legacy event log persistence removed in oneof refactor.
-	if len(messages) == 0 {
+	return nil
-		return nil
-	}
-	log.Printf("%d messages to save for grain id %s", len(messages), id)
-	var file *os.File
-	var err error
-	path := getCartPath(id.String())
-	file, err = os.OpenFile(path, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
-	if err != nil {
-		return err
-	}
-	defer file.Close()
-
-	for _, m := range messages {
-		err := m.Write(file)
-		if err != nil {
-			return err
-		}
-	}
-	return err
 }
 
 func getCartPath(id string) string {
 	return fmt.Sprintf("data/%s.prot", id)
 }
 
-func loadMessages(grain Grain, id CartId) error {
+func loadMessages(_ Grain, _ CartId) error {
-	var err error
+	// No-op: legacy replay removed in oneof refactor.
-	path := getCartPath(id.String())
+	return nil
-
-	file, err := os.Open(path)
-	if err != nil {
-		if os.IsNotExist(err) {
-			return nil
-		}
-		return err
-	}
-	defer file.Close()
-
-	for err == nil {
-		var msg Message
-		err = ReadMessage(file, &msg)
-		if err == nil {
-			grain.HandleMessage(&msg, true)
-		}
-	}
-
-	if err.Error() == "EOF" {
-		return nil
-	}
-	return err
 }
 
 func (s *DiskStorage) saveState() error {
@@ -103,15 +61,8 @@ func (s *DiskStorage) loadState() error {
 	return gob.NewDecoder(file).Decode(&s.LastSaves)
 }
 
-func (s *DiskStorage) Store(id CartId, grain *CartGrain) error {
+func (s *DiskStorage) Store(id CartId, _ *CartGrain) error {
-	lastSavedMessage, ok := s.LastSaves[id]
+	// With the removal of the legacy message log, we only update the timestamp.
-	if ok && lastSavedMessage > grain.GetLastChange() {
-		return nil
-	}
-	err := saveMessages(grain.GetStorageMessage(lastSavedMessage), id)
-	if err != nil {
-		return err
-	}
 	ts := time.Now().Unix()
 	s.LastSaves[id] = ts
 	s.lastSave = ts

frames.go

@@ -1,102 +0,0 @@
-package main
-
-// Minimal frame abstractions retained after removal of the legacy TCP/frame
-// networking layer. These types remain only to avoid a wide cascading refactor
-// across existing grain / pool logic that still constructs and passes
-// FrameWithPayload objects internally.
-//
-// The original responsibilities this replaces:
-//   - Binary framing, checksums, network IO
-//   - Distinction between request / reply frame types
-//
-// What remains:
-//   - A light weight container (FrameWithPayload) used as an in‑process
-//     envelope for status code + typed marker + payload bytes (JSON or proto).
-//   - Message / status constants referenced in existing code paths.
-//
-// Recommended future cleanup (post‑migration):
-//   - Remove FrameType entirely and replace with enumerated semantic results
-//     or error values.
-//   - Replace FrameWithPayload with a struct { Status int; Data []byte }.
-//   - Remove remote_* reply type branching once all callers rely on gRPC
-//     status + strongly typed responses.
-//
-// For now we keep this minimal surface to keep the gRPC migration focused.
-
-type (
-	// FrameType is a symbolic identifier carried through existing code paths.
-	// No ordering or bit semantics are required anymore.
-	FrameType  uint32
-	StatusCode uint32
-)
-
-type Frame struct {
-	Type       FrameType
-	StatusCode StatusCode
-	Length     uint32
-	// Checksum retained for compatibility; no longer validated.
-	Checksum uint32
-}
-
-// FrameWithPayload wraps a Frame with an opaque payload.
-// Payload usually contains JSON encoded cart state or an error message.
-type FrameWithPayload struct {
-	Frame
-	Payload []byte
-}
-
-// -----------------------------------------------------------------------------
-// Legacy Frame Type Constants (minimal subset still referenced)
-// -----------------------------------------------------------------------------
-const (
-	RemoteGetState            = FrameType(0x01)
-	RemoteHandleMutation      = FrameType(0x02)
-	ResponseBody              = FrameType(0x03) // (rarely used; kept for completeness)
-	RemoteGetStateReply       = FrameType(0x04)
-	RemoteHandleMutationReply = FrameType(0x05)
-	RemoteCreateOrderReply    = FrameType(0x06)
-)
-
-// MakeFrameWithPayload constructs an in‑process frame wrapper.
-// Length & Checksum are filled for backward compatibility (no validation logic
-// depends on the checksum anymore).
-func MakeFrameWithPayload(msg FrameType, statusCode StatusCode, payload []byte) FrameWithPayload {
-	length := uint32(len(payload))
-	return FrameWithPayload{
-		Frame: Frame{
-			Type:       msg,
-			StatusCode: statusCode,
-			Length:     length,
-			Checksum:   (uint32(msg) + uint32(statusCode) + length) / 8, // simple legacy formula
-		},
-		Payload: payload,
-	}
-}
-
-// Clone creates a shallow copy of the frame, duplicating the payload slice.
-func (f *FrameWithPayload) Clone() *FrameWithPayload {
-	if f == nil {
-		return nil
-	}
-	cp := make([]byte, len(f.Payload))
-	copy(cp, f.Payload)
-	return &FrameWithPayload{
-		Frame:   f.Frame,
-		Payload: cp,
-	}
-}
-
-// NewErrorFrame helper for creating an error frame with a textual payload.
-func NewErrorFrame(msg FrameType, code StatusCode, err error) FrameWithPayload {
-	var b []byte
-	if err != nil {
-		b = []byte(err.Error())
-	}
-	return MakeFrameWithPayload(msg, code, b)
-}
-
-// IsSuccess returns true if the status code indicates success in the
-// conventional HTTP style range (200–299). This mirrors previous usage patterns.
-func (f *FrameWithPayload) IsSuccess() bool {
-	return f != nil && f.StatusCode >= 200 && f.StatusCode < 300
-}

grain-pool.go

@@ -1,7 +1,6 @@
 package main
 
 import (
-	"encoding/json"
 	"fmt"
 	"log"
 	"sync"
@@ -11,6 +10,23 @@ import (
 	"github.com/prometheus/client_golang/prometheus/promauto"
 )
 
+// grain-pool.go
+//
+// Migration Note:
+//   This file has been migrated to use uint64 cart keys internally (derived
+//   from the new CartID base62 representation). For backward compatibility,
+//   a deprecated legacy map keyed by CartId is maintained so existing code
+//   that directly indexes pool.grains with a CartId continues to compile
+//   until the full refactor across SyncedPool / remoteIndex is completed.
+//
+//   Authoritative storage: grains (map[uint64]*CartGrain)
+//   Legacy compatibility:  grainsLegacy (map[CartId]*CartGrain) - kept in sync.
+//
+//   Once all external usages are updated to rely on helper accessors,
+//   grainsLegacy can be removed.
+//
+// ---------------------------------------------------------------------------
+
 var (
 	poolGrains = promauto.NewGauge(prometheus.GaugeOpts{
 		Name: "cart_grains_in_pool",
@@ -26,49 +42,71 @@ var (
 	})
 )
 
+// GrainPool interface remains legacy-compatible.
 type GrainPool interface {
-	Process(id CartId, messages ...Message) (*FrameWithPayload, error)
+	Apply(id CartId, mutation interface{}) (*CartGrain, error)
-	Get(id CartId) (*FrameWithPayload, error)
+	Get(id CartId) (*CartGrain, error)
 }
 
+// Ttl keeps expiry info
 type Ttl struct {
 	Expires time.Time
 	Grain   *CartGrain
 }
 
+// GrainLocalPool now stores grains keyed by uint64 (CartKey).
 type GrainLocalPool struct {
 	mu       sync.RWMutex
-	grains   map[CartId]*CartGrain
+	grains   map[uint64]*CartGrain // authoritative only
 	expiry   []Ttl
 	spawn    func(id CartId) (*CartGrain, error)
 	Ttl      time.Duration
 	PoolSize int
 }
 
+// NewGrainLocalPool constructs a new pool.
 func NewGrainLocalPool(size int, ttl time.Duration, spawn func(id CartId) (*CartGrain, error)) *GrainLocalPool {
-
 	ret := &GrainLocalPool{
 		spawn:    spawn,
-		grains:   make(map[CartId]*CartGrain),
+		grains:   make(map[uint64]*CartGrain),
 		expiry:   make([]Ttl, 0),
 		Ttl:      ttl,
 		PoolSize: size,
 	}
-
 	cartPurge := time.NewTicker(time.Minute)
 	go func() {
-		<-cartPurge.C
+		for range cartPurge.C {
-		ret.Purge()
+			ret.Purge()
+		}
 	}()
 	return ret
 }
 
+// keyFromCartId derives the uint64 key from a legacy CartId deterministically.
+func keyFromCartId(id CartId) uint64 {
+	return LegacyToCartKey(id)
+}
+
+// storeGrain indexes a grain in both maps.
+func (p *GrainLocalPool) storeGrain(id CartId, g *CartGrain) {
+	k := keyFromCartId(id)
+	p.grains[k] = g
+}
+
+// deleteGrain removes a grain from both maps.
+func (p *GrainLocalPool) deleteGrain(id CartId) {
+	k := keyFromCartId(id)
+	delete(p.grains, k)
+}
+
+// SetAvailable pre-populates placeholder entries (legacy signature).
 func (p *GrainLocalPool) SetAvailable(availableWithLastChangeUnix map[CartId]int64) {
 	p.mu.Lock()
 	defer p.mu.Unlock()
 	for id := range availableWithLastChangeUnix {
-		if _, ok := p.grains[id]; !ok {
+		k := keyFromCartId(id)
-			p.grains[id] = nil
+		if _, ok := p.grains[k]; !ok {
+			p.grains[k] = nil
 			p.expiry = append(p.expiry, Ttl{
 				Expires: time.Now().Add(p.Ttl),
 				Grain:   nil,
@@ -77,13 +115,19 @@ func (p *GrainLocalPool) SetAvailable(availableWithLastChangeUnix map[CartId]int
 	}
 }
 
+// Purge removes expired grains.
 func (p *GrainLocalPool) Purge() {
 	lastChangeTime := time.Now().Add(-p.Ttl)
 	keepChanged := lastChangeTime.Unix()
+
 	p.mu.Lock()
 	defer p.mu.Unlock()
+
 	for i := 0; i < len(p.expiry); i++ {
 		item := p.expiry[i]
+		if item.Grain == nil {
+			continue
+		}
 		if item.Expires.Before(time.Now()) {
 			if item.Grain.GetLastChange() > keepChanged {
 				log.Printf("Expired item %s changed, keeping", item.Grain.GetId())
@@ -91,12 +135,12 @@ func (p *GrainLocalPool) Purge() {
 					p.expiry = append(p.expiry[:i], p.expiry[i+1:]...)
 					p.expiry = append(p.expiry, item)
 				} else {
+					// move last to end (noop)
 					p.expiry = append(p.expiry[:i], item)
 				}
-
 			} else {
 				log.Printf("Item %s expired", item.Grain.GetId())
-				delete(p.grains, item.Grain.GetId())
+				p.deleteGrain(item.Grain.GetId())
 				if i < len(p.expiry)-1 {
 					p.expiry = append(p.expiry[:i], p.expiry[i+1:]...)
 				} else {
@@ -109,60 +153,92 @@ func (p *GrainLocalPool) Purge() {
 	}
 }
 
+// GetGrains returns a legacy view of grains (copy) for compatibility.
 func (p *GrainLocalPool) GetGrains() map[CartId]*CartGrain {
-	return p.grains
+	p.mu.RLock()
+	defer p.mu.RUnlock()
+	out := make(map[CartId]*CartGrain, len(p.grains))
+	for _, g := range p.grains {
+		if g != nil {
+			out[g.GetId()] = g
+		}
+	}
+	return out
 }
 
-func (p *GrainLocalPool) GetGrain(id CartId) (*CartGrain, error) {
+// statsUpdate updates Prometheus gauges asynchronously.
-	var err error
+func (p *GrainLocalPool) statsUpdate() {
-	// p.mu.RLock()
+	go func(size int) {
-	// defer p.mu.RUnlock()
+		l := float64(size)
-	grain, ok := p.grains[id]
-	grainLookups.Inc()
-	if grain == nil || !ok {
-		if len(p.grains) >= p.PoolSize {
-			if p.expiry[0].Expires.Before(time.Now()) {
-				delete(p.grains, p.expiry[0].Grain.GetId())
-				p.expiry = p.expiry[1:]
-			} else {
-				return nil, fmt.Errorf("pool is full")
-			}
-		}
-		grain, err = p.spawn(id)
-		p.mu.Lock()
-		p.grains[id] = grain
-		p.mu.Unlock()
-	}
-	go func() {
-		l := float64(len(p.grains))
 		ps := float64(p.PoolSize)
 		poolUsage.Set(l / ps)
 		poolGrains.Set(l)
 		poolSize.Set(ps)
-	}()
+	}(len(p.grains))
+}
+
+// GetGrain retrieves or spawns a grain (legacy id signature).
+func (p *GrainLocalPool) GetGrain(id CartId) (*CartGrain, error) {
+	grainLookups.Inc()
+	k := keyFromCartId(id)
+
+	p.mu.RLock()
+	grain, ok := p.grains[k]
+	p.mu.RUnlock()
+
+	var err error
+	if grain == nil || !ok {
+		p.mu.Lock()
+		// Re-check under write lock
+		grain, ok = p.grains[k]
+		if grain == nil || !ok {
+			// Capacity check
+			if len(p.grains) >= p.PoolSize && len(p.expiry) > 0 {
+				if p.expiry[0].Expires.Before(time.Now()) && p.expiry[0].Grain != nil {
+					oldId := p.expiry[0].Grain.GetId()
+					p.deleteGrain(oldId)
+					p.expiry = p.expiry[1:]
+				} else {
+					p.mu.Unlock()
+					return nil, fmt.Errorf("pool is full")
+				}
+			}
+			grain, err = p.spawn(id)
+			if err == nil {
+				p.storeGrain(id, grain)
+			}
+		}
+		p.mu.Unlock()
+		p.statsUpdate()
+	}
+
 	return grain, err
 }
 
-func (p *GrainLocalPool) Process(id CartId, messages ...Message) (*FrameWithPayload, error) {
+// Apply applies a mutation (legacy compatibility).
+func (p *GrainLocalPool) Apply(id CartId, mutation interface{}) (*CartGrain, error) {
 	grain, err := p.GetGrain(id)
-	var result *FrameWithPayload
+	if err != nil || grain == nil {
-	if err == nil && grain != nil {
+		return nil, err
-		for _, message := range messages {
-			result, err = grain.HandleMessage(&message, false)
-		}
 	}
-	return result, err
+	return grain.Apply(mutation, false)
 }
 
-func (p *GrainLocalPool) Get(id CartId) (*FrameWithPayload, error) {
+// Get returns current state (legacy wrapper).
-	grain, err := p.GetGrain(id)
+func (p *GrainLocalPool) Get(id CartId) (*CartGrain, error) {
-	if err != nil {
+	return p.GetGrain(id)
-		return nil, err
+}
-	}
+
-	data, err := json.Marshal(grain)
+// DebugGrainCount returns counts for debugging.
-	if err != nil {
+func (p *GrainLocalPool) DebugGrainCount() (authoritative int) {
-		return nil, err
+	p.mu.RLock()
-	}
+	defer p.mu.RUnlock()
-	ret := MakeFrameWithPayload(0, 200, data)
+	return len(p.grains)
-	return &ret, nil
+}
+
+// UnsafePointerToLegacyMap exposes the legacy map pointer (for transitional
+// tests that still poke the field directly). DO NOT rely on this long-term.
+func (p *GrainLocalPool) UnsafePointerToLegacyMap() uintptr {
+	// Legacy map removed; retained only to satisfy any transitional callers.
+	return 0
 }

grpc_integration_test.go

@@ -1,9 +1,7 @@
 package main
 
 import (
-	"bytes"
 	"context"
-	"encoding/json"
 	"fmt"
 	"testing"
 	"time"
@@ -14,7 +12,7 @@ import (
 
 // TestCartActorMutationAndState validates end-to-end gRPC mutation + state retrieval
 // against a locally started gRPC server (single-node scenario).
-// This test uses AddItemType directly to avoid hitting external product
+// This test uses the new per-mutation AddItem RPC (breaking v2 API) to avoid external product fetch logic
 // fetching logic (FetchItem) which would require network I/O.
 func TestCartActorMutationAndState(t *testing.T) {
 	// Setup local grain pool + synced pool (no discovery, single host)
@@ -62,37 +60,29 @@ func TestCartActorMutationAndState(t *testing.T) {
 		Country:  "se",
 	}
 
-	// Marshal underlying mutation payload using the existing handler code path
+	// Issue AddItem RPC directly (breaking v2 API)
-	handler, ok := Handlers[AddItemType]
+	addResp, err := cartClient.AddItem(context.Background(), &messages.AddItemRequest{
-	if !ok {
-		t.Fatalf("Handler for AddItemType missing")
-	}
-	payloadData, err := getSerializedPayload(handler, AddItemType, addItem)
-	if err != nil {
-		t.Fatalf("serialize add item: %v", err)
-	}
-
-	// Issue Mutate RPC
-	mutResp, err := cartClient.Mutate(context.Background(), &messages.MutationRequest{
 		CartId:          cartID,
-		Type:            messages.MutationType(AddItemType),
-		Payload:         payloadData,
 		ClientTimestamp: time.Now().Unix(),
+		Payload:         addItem,
 	})
 	if err != nil {
-		t.Fatalf("Mutate RPC error: %v", err)
+		t.Fatalf("AddItem RPC error: %v", err)
 	}
-	if mutResp.StatusCode != 200 {
+	if addResp.StatusCode != 200 {
-		t.Fatalf("Mutate returned non-200 status: %d payload=%s", mutResp.StatusCode, string(mutResp.Payload))
+		t.Fatalf("AddItem returned non-200 status: %d, error: %s", addResp.StatusCode, addResp.GetError())
 	}
 
-	// Decode cart state JSON and validate
+	// Validate the response state (from AddItem)
-	state := &CartGrain{}
+	state := addResp.GetState()
-	if err := json.Unmarshal(mutResp.Payload, state); err != nil {
+	if state == nil {
-		t.Fatalf("Unmarshal mutate cart state: %v\nPayload: %s", err, string(mutResp.Payload))
+		t.Fatalf("AddItem response state is nil")
 	}
+
+	// (Removed obsolete Mutate response handling)
+
 	if len(state.Items) != 1 {
-		t.Fatalf("Expected 1 item after mutation, got %d", len(state.Items))
+		t.Fatalf("Expected 1 item after AddItem, got %d", len(state.Items))
 	}
 	if state.Items[0].Sku != "test-sku" {
 		t.Fatalf("Unexpected item SKU: %s", state.Items[0].Sku)
@@ -106,13 +96,14 @@ func TestCartActorMutationAndState(t *testing.T) {
 		t.Fatalf("GetState RPC error: %v", err)
 	}
 	if getResp.StatusCode != 200 {
-		t.Fatalf("GetState returned non-200 status: %d payload=%s", getResp.StatusCode, string(getResp.Payload))
+		t.Fatalf("GetState returned non-200 status: %d, error: %s", getResp.StatusCode, getResp.GetError())
 	}
 
-	state2 := &CartGrain{}
+	state2 := getResp.GetState()
-	if err := json.Unmarshal(getResp.Payload, state2); err != nil {
+	if state2 == nil {
-		t.Fatalf("Unmarshal get state: %v", err)
+		t.Fatalf("GetState response state is nil")
 	}
+
 	if len(state2.Items) != 1 {
 		t.Fatalf("Expected 1 item in GetState, got %d", len(state2.Items))
 	}
@@ -121,15 +112,4 @@ func TestCartActorMutationAndState(t *testing.T) {
 	}
 }
 
-// getSerializedPayload serializes a mutation proto using the registered handler.
+// Legacy serialization helper removed (oneof envelope used directly)
-func getSerializedPayload(handler MessageHandler, msgType uint16, content interface{}) ([]byte, error) {
-	msg := &Message{
-		Type:    msgType,
-		Content: content,
-	}
-	var buf bytes.Buffer
-	if err := handler.Write(msg, &buf); err != nil {
-		return nil, err
-	}
-	return buf.Bytes(), nil
-}

grpc_server.go

@@ -2,378 +2,279 @@ package main
 
 import (
 	"context"
-	"errors"
 	"fmt"
 	"log"
 	"net"
 	"time"
 
-	proto "git.tornberg.me/go-cart-actor/proto" // underlying generated package name is 'messages'
+	messages "git.tornberg.me/go-cart-actor/proto"
-	"github.com/prometheus/client_golang/prometheus"
-	"github.com/prometheus/client_golang/prometheus/promauto"
 	"google.golang.org/grpc"
-	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/reflection"
-	"google.golang.org/grpc/status"
 )
 
-// -----------------------------------------------------------------------------
+// cartActorGRPCServer implements the CartActor and ControlPlane gRPC services.
-// Metrics
+// It delegates cart operations to a grain pool and cluster operations to a synced pool.
-// -----------------------------------------------------------------------------
+type cartActorGRPCServer struct {
+	messages.UnimplementedCartActorServer
+	messages.UnimplementedControlPlaneServer
 
-var (
+	pool       GrainPool   // For cart state mutations and queries
-	grpcMutateDuration = promauto.NewHistogram(prometheus.HistogramOpts{
+	syncedPool *SyncedPool // For cluster membership and control
-		Name:    "cart_grpc_mutate_duration_seconds",
-		Help:    "Duration of CartActor.Mutate RPCs",
-		Buckets: prometheus.DefBuckets,
-	})
-	grpcMutateErrors = promauto.NewCounter(prometheus.CounterOpts{
-		Name: "cart_grpc_mutate_errors_total",
-		Help: "Total number of failed CartActor.Mutate RPCs",
-	})
-	grpcStateDuration = promauto.NewHistogram(prometheus.HistogramOpts{
-		Name:    "cart_grpc_get_state_duration_seconds",
-		Help:    "Duration of CartActor.GetState RPCs",
-		Buckets: prometheus.DefBuckets,
-	})
-	grpcControlDuration = promauto.NewHistogram(prometheus.HistogramOpts{
-		Name:    "cart_grpc_control_duration_seconds",
-		Help:    "Duration of ControlPlane RPCs",
-		Buckets: prometheus.DefBuckets,
-	})
-	grpcControlErrors = promauto.NewCounter(prometheus.CounterOpts{
-		Name: "cart_grpc_control_errors_total",
-		Help: "Total number of failed ControlPlane RPCs",
-	})
-)
-
-// timeTrack wraps a closure and records duration into the supplied histogram.
-func timeTrack(hist prometheus.Observer, fn func() error) (err error) {
-	start := time.Now()
-	defer func() {
-		hist.Observe(time.Since(start).Seconds())
-	}()
-	return fn()
 }
 
-// -----------------------------------------------------------------------------
+// NewCartActorGRPCServer creates and initializes the server.
-// CartActor Service Implementation
+func NewCartActorGRPCServer(pool GrainPool, syncedPool *SyncedPool) *cartActorGRPCServer {
-// -----------------------------------------------------------------------------
+	return &cartActorGRPCServer{
-
+		pool:       pool,
-type cartActorService struct {
+		syncedPool: syncedPool,
-	proto.UnimplementedCartActorServer
+	}
-	pool GrainPool
 }
 
-func newCartActorService(pool GrainPool) *cartActorService {
+// applyMutation routes a single cart mutation to the target grain (used by per-mutation RPC handlers).
-	return &cartActorService{pool: pool}
+func (s *cartActorGRPCServer) applyMutation(cartID string, mutation interface{}) *messages.CartMutationReply {
-}
+	// Canonicalize or preserve legacy id (do NOT hash-rewrite legacy textual ids)
-
+	cid, _, wasBase62, cerr := CanonicalizeOrLegacy(cartID)
-func (s *cartActorService) Mutate(ctx context.Context, req *proto.MutationRequest) (*proto.MutationReply, error) {
+	if cerr != nil {
-	var reply *proto.MutationReply
+		return &messages.CartMutationReply{
-	err := timeTrack(grpcMutateDuration, func() error {
+			StatusCode:      500,
-		if req == nil {
+			Result:          &messages.CartMutationReply_Error{Error: fmt.Sprintf("cart_id canonicalization failed: %v", cerr)},
-			return status.Error(codes.InvalidArgument, "request is nil")
+			ServerTimestamp: time.Now().Unix(),
 		}
-		if req.CartId == "" {
+	}
-			return status.Error(codes.InvalidArgument, "cart_id is empty")
+	_ = wasBase62 // placeholder; future: propagate canonical id in reply metadata
-		}
+	legacy := CartIDToLegacy(cid)
-		mt := uint16(req.Type.Number())
+	grain, err := s.pool.Apply(legacy, mutation)
-		handler, ok := Handlers[mt]
-		if !ok {
-			return status.Errorf(codes.InvalidArgument, "unknown mutation type %d", mt)
-		}
-		content, err := handler.Read(req.Payload)
-		if err != nil {
-			return status.Errorf(codes.InvalidArgument, "decode payload: %v", err)
-		}
-
-		ts := req.ClientTimestamp
-		if ts == 0 {
-			ts = time.Now().Unix()
-		}
-		msg := Message{
-			Type:      mt,
-			TimeStamp: &ts,
-			Content:   content,
-		}
-
-		frame, err := s.pool.Process(ToCartId(req.CartId), msg)
-		if err != nil {
-			return err
-		}
-		reply = &proto.MutationReply{
-			StatusCode: int32(frame.StatusCode),
-			Payload:    frame.Payload,
-		}
-		return nil
-	})
 	if err != nil {
-		grpcMutateErrors.Inc()
+		return &messages.CartMutationReply{
-		return nil, err
+			StatusCode:      500,
+			Result:          &messages.CartMutationReply_Error{Error: err.Error()},
+			ServerTimestamp: time.Now().Unix(),
+		}
+	}
+	cartState := ToCartState(grain)
+	return &messages.CartMutationReply{
+		StatusCode:      200,
+		Result:          &messages.CartMutationReply_State{State: cartState},
+		ServerTimestamp: time.Now().Unix(),
 	}
-	return reply, nil
 }
 
-func (s *cartActorService) GetState(ctx context.Context, req *proto.StateRequest) (*proto.StateReply, error) {
+func (s *cartActorGRPCServer) AddRequest(ctx context.Context, req *messages.AddRequestRequest) (*messages.CartMutationReply, error) {
-	var reply *proto.StateReply
+	if req.GetCartId() == "" {
-	err := timeTrack(grpcStateDuration, func() error {
+		return &messages.CartMutationReply{
-		if req == nil || req.CartId == "" {
+			StatusCode:      400,
-			return status.Error(codes.InvalidArgument, "cart_id is empty")
+			Result:          &messages.CartMutationReply_Error{Error: "cart_id is required"},
-		}
+			ServerTimestamp: time.Now().Unix(),
-		frame, err := s.pool.Get(ToCartId(req.CartId))
+		}, nil
-		if err != nil {
+	}
-			return err
+	return s.applyMutation(req.GetCartId(), req.GetPayload()), nil
-		}
+}
-		reply = &proto.StateReply{
+
-			StatusCode: int32(frame.StatusCode),
+func (s *cartActorGRPCServer) AddItem(ctx context.Context, req *messages.AddItemRequest) (*messages.CartMutationReply, error) {
-			Payload:    frame.Payload,
+	if req.GetCartId() == "" {
-		}
+		return &messages.CartMutationReply{
-		return nil
+			StatusCode:      400,
-	})
+			Result:          &messages.CartMutationReply_Error{Error: "cart_id is required"},
+			ServerTimestamp: time.Now().Unix(),
+		}, nil
+	}
+	return s.applyMutation(req.GetCartId(), req.GetPayload()), nil
+}
+
+func (s *cartActorGRPCServer) RemoveItem(ctx context.Context, req *messages.RemoveItemRequest) (*messages.CartMutationReply, error) {
+	if req.GetCartId() == "" {
+		return &messages.CartMutationReply{
+			StatusCode:      400,
+			Result:          &messages.CartMutationReply_Error{Error: "cart_id is required"},
+			ServerTimestamp: time.Now().Unix(),
+		}, nil
+	}
+	return s.applyMutation(req.GetCartId(), req.GetPayload()), nil
+}
+
+func (s *cartActorGRPCServer) RemoveDelivery(ctx context.Context, req *messages.RemoveDeliveryRequest) (*messages.CartMutationReply, error) {
+	if req.GetCartId() == "" {
+		return &messages.CartMutationReply{
+			StatusCode:      400,
+			Result:          &messages.CartMutationReply_Error{Error: "cart_id is required"},
+			ServerTimestamp: time.Now().Unix(),
+		}, nil
+	}
+	return s.applyMutation(req.GetCartId(), req.GetPayload()), nil
+}
+
+func (s *cartActorGRPCServer) ChangeQuantity(ctx context.Context, req *messages.ChangeQuantityRequest) (*messages.CartMutationReply, error) {
+	if req.GetCartId() == "" {
+		return &messages.CartMutationReply{
+			StatusCode:      400,
+			Result:          &messages.CartMutationReply_Error{Error: "cart_id is required"},
+			ServerTimestamp: time.Now().Unix(),
+		}, nil
+	}
+	return s.applyMutation(req.GetCartId(), req.GetPayload()), nil
+}
+
+func (s *cartActorGRPCServer) SetDelivery(ctx context.Context, req *messages.SetDeliveryRequest) (*messages.CartMutationReply, error) {
+	if req.GetCartId() == "" {
+		return &messages.CartMutationReply{
+			StatusCode:      400,
+			Result:          &messages.CartMutationReply_Error{Error: "cart_id is required"},
+			ServerTimestamp: time.Now().Unix(),
+		}, nil
+	}
+	return s.applyMutation(req.GetCartId(), req.GetPayload()), nil
+}
+
+func (s *cartActorGRPCServer) SetPickupPoint(ctx context.Context, req *messages.SetPickupPointRequest) (*messages.CartMutationReply, error) {
+	if req.GetCartId() == "" {
+		return &messages.CartMutationReply{
+			StatusCode:      400,
+			Result:          &messages.CartMutationReply_Error{Error: "cart_id is required"},
+			ServerTimestamp: time.Now().Unix(),
+		}, nil
+	}
+	return s.applyMutation(req.GetCartId(), req.GetPayload()), nil
+}
+
+/*
+Checkout RPC removed. Checkout is handled at the HTTP layer (PoolServer.HandleCheckout).
+*/
+
+func (s *cartActorGRPCServer) SetCartItems(ctx context.Context, req *messages.SetCartItemsRequest) (*messages.CartMutationReply, error) {
+	if req.GetCartId() == "" {
+		return &messages.CartMutationReply{
+			StatusCode:      400,
+			Result:          &messages.CartMutationReply_Error{Error: "cart_id is required"},
+			ServerTimestamp: time.Now().Unix(),
+		}, nil
+	}
+	return s.applyMutation(req.GetCartId(), req.GetPayload()), nil
+}
+
+func (s *cartActorGRPCServer) OrderCompleted(ctx context.Context, req *messages.OrderCompletedRequest) (*messages.CartMutationReply, error) {
+	if req.GetCartId() == "" {
+		return &messages.CartMutationReply{
+			StatusCode:      400,
+			Result:          &messages.CartMutationReply_Error{Error: "cart_id is required"},
+			ServerTimestamp: time.Now().Unix(),
+		}, nil
+	}
+	return s.applyMutation(req.GetCartId(), req.GetPayload()), nil
+}
+
+// GetState retrieves the current state of a cart grain.
+func (s *cartActorGRPCServer) GetState(ctx context.Context, req *messages.StateRequest) (*messages.StateReply, error) {
+	if req.GetCartId() == "" {
+		return &messages.StateReply{
+			StatusCode: 400,
+			Result:     &messages.StateReply_Error{Error: "cart_id is required"},
+		}, nil
+	}
+	// Canonicalize / upgrade incoming cart id (preserve legacy strings)
+	cid, _, _, cerr := CanonicalizeOrLegacy(req.GetCartId())
+	if cerr != nil {
+		return &messages.StateReply{
+			StatusCode: 500,
+			Result:     &messages.StateReply_Error{Error: fmt.Sprintf("cart_id canonicalization failed: %v", cerr)},
+		}, nil
+	}
+	legacy := CartIDToLegacy(cid)
+
+	grain, err := s.pool.Get(legacy)
 	if err != nil {
-		return nil, err
+		return &messages.StateReply{
-	}
+			StatusCode: 500,
-	return reply, nil
+			Result:     &messages.StateReply_Error{Error: err.Error()},
-}
+		}, nil
-
-// -----------------------------------------------------------------------------
-// ControlPlane Service Implementation
-// -----------------------------------------------------------------------------
-
-// controlPlaneService directly leverages SyncedPool internals (same package).
-// NOTE: This is a transitional adapter; once the legacy frame-based code is
-// removed, related fields/methods in SyncedPool can be slimmed.
-type controlPlaneService struct {
-	proto.UnimplementedControlPlaneServer
-	pool *SyncedPool
-}
-
-func newControlPlaneService(pool *SyncedPool) *controlPlaneService {
-	return &controlPlaneService{pool: pool}
-}
-
-func (s *controlPlaneService) Ping(ctx context.Context, _ *proto.Empty) (*proto.PingReply, error) {
-	var reply *proto.PingReply
-	err := timeTrack(grpcControlDuration, func() error {
-		reply = &proto.PingReply{
-			Host:     s.pool.Hostname,
-			UnixTime: time.Now().Unix(),
-		}
-		return nil
-	})
-	if err != nil {
-		grpcControlErrors.Inc()
-		return nil, err
-	}
-	return reply, nil
-}
-
-func (s *controlPlaneService) Negotiate(ctx context.Context, req *proto.NegotiateRequest) (*proto.NegotiateReply, error) {
-	var reply *proto.NegotiateReply
-	err := timeTrack(grpcControlDuration, func() error {
-		if req == nil {
-			return status.Error(codes.InvalidArgument, "request is nil")
-		}
-		// Add unknown hosts
-		for _, host := range req.KnownHosts {
-			if host == "" || host == s.pool.Hostname {
-				continue
-			}
-			if !s.pool.IsKnown(host) {
-				go s.pool.AddRemote(host)
-			}
-		}
-		// Build healthy host list
-		hosts := make([]string, 0)
-		for _, r := range s.pool.GetHealthyRemotes() {
-			hosts = append(hosts, r.Host)
-		}
-		hosts = append(hosts, s.pool.Hostname)
-		reply = &proto.NegotiateReply{
-			Hosts: hosts,
-		}
-		return nil
-	})
-	if err != nil {
-		grpcControlErrors.Inc()
-		return nil, err
-	}
-	return reply, nil
-}
-
-func (s *controlPlaneService) GetCartIds(ctx context.Context, _ *proto.Empty) (*proto.CartIdsReply, error) {
-	var reply *proto.CartIdsReply
-	err := timeTrack(grpcControlDuration, func() error {
-		s.pool.mu.RLock()
-		defer s.pool.mu.RUnlock()
-		ids := make([]string, 0, len(s.pool.local.grains))
-		for id, g := range s.pool.local.grains {
-			if g == nil {
-				continue
-			}
-			if id.String() == "" {
-				continue
-			}
-			ids = append(ids, id.String())
-		}
-		reply = &proto.CartIdsReply{
-			CartIds: ids,
-		}
-		return nil
-	})
-	if err != nil {
-		grpcControlErrors.Inc()
-		return nil, err
-	}
-	return reply, nil
-}
-
-func (s *controlPlaneService) ConfirmOwner(ctx context.Context, req *proto.OwnerChangeRequest) (*proto.OwnerChangeAck, error) {
-	var reply *proto.OwnerChangeAck
-	err := timeTrack(grpcControlDuration, func() error {
-		if req == nil || req.CartId == "" || req.NewHost == "" {
-			return status.Error(codes.InvalidArgument, "cart_id or new_host missing")
-		}
-		id := ToCartId(req.CartId)
-		newHost := req.NewHost
-
-		// Mirror GrainOwnerChangeHandler semantics
-		log.Printf("gRPC ConfirmOwner: cart %s newHost=%s", id, newHost)
-		for _, r := range s.pool.remoteHosts {
-			if r.Host == newHost && r.IsHealthy() {
-				go s.pool.SpawnRemoteGrain(id, newHost)
-				break
-			}
-		}
-		go s.pool.AddRemote(newHost)
-
-		reply = &proto.OwnerChangeAck{
-			Accepted: true,
-			Message:  "ok",
-		}
-		return nil
-	})
-	if err != nil {
-		grpcControlErrors.Inc()
-		return nil, err
-	}
-	return reply, nil
-}
-
-func (s *controlPlaneService) Closing(ctx context.Context, notice *proto.ClosingNotice) (*proto.OwnerChangeAck, error) {
-	var reply *proto.OwnerChangeAck
-	err := timeTrack(grpcControlDuration, func() error {
-		if notice == nil || notice.Host == "" {
-			return status.Error(codes.InvalidArgument, "host missing")
-		}
-		host := notice.Host
-		s.pool.mu.RLock()
-		_, exists := s.pool.remoteHosts[host]
-		s.pool.mu.RUnlock()
-		if exists {
-			go s.pool.RemoveHost(host)
-		}
-		reply = &proto.OwnerChangeAck{
-			Accepted: true,
-			Message:  "removed",
-		}
-		return nil
-	})
-	if err != nil {
-		grpcControlErrors.Inc()
-		return nil, err
-	}
-	return reply, nil
-}
-
-// -----------------------------------------------------------------------------
-// Server Bootstrap
-// -----------------------------------------------------------------------------
-
-type GRPCServer struct {
-	server *grpc.Server
-	lis    net.Listener
-	addr   string
-}
-
-// StartGRPCServer sets up a gRPC server hosting both CartActor and ControlPlane services.
-// addr example: ":1337" (for combined) OR run two servers if you want separate ports.
-// For the migration we can host both on the same listener to reduce open ports.
-func StartGRPCServer(addr string, pool GrainPool, synced *SyncedPool, opts ...grpc.ServerOption) (*GRPCServer, error) {
-	if pool == nil {
-		return nil, errors.New("nil grain pool")
-	}
-	if synced == nil {
-		return nil, errors.New("nil synced pool")
 	}
 
-	lis, err := net.Listen("tcp", addr)
+	cartState := ToCartState(grain)
-	if err != nil {
-		return nil, fmt.Errorf("listen %s: %w", addr, err)
-	}
 
-	grpcServer := grpc.NewServer(opts...)
+	return &messages.StateReply{
-	proto.RegisterCartActorServer(grpcServer, newCartActorService(pool))
+		StatusCode: 200,
-	proto.RegisterControlPlaneServer(grpcServer, newControlPlaneService(synced))
+		Result:     &messages.StateReply_State{State: cartState},
-
-	go func() {
-		log.Printf("gRPC server listening on %s", addr)
-		if serveErr := grpcServer.Serve(lis); serveErr != nil {
-			log.Printf("gRPC server stopped: %v", serveErr)
-		}
-	}()
-
-	return &GRPCServer{
-		server: grpcServer,
-		lis:    lis,
-		addr:   addr,
 	}, nil
 }
 
-// GracefulStop stops the server gracefully.
+// ControlPlane: Ping
-func (s *GRPCServer) GracefulStop() {
+func (s *cartActorGRPCServer) Ping(ctx context.Context, _ *messages.Empty) (*messages.PingReply, error) {
-	if s == nil || s.server == nil {
+	return &messages.PingReply{
-		return
+		Host:     s.syncedPool.Hostname,
-	}
+		UnixTime: time.Now().Unix(),
-	s.server.GracefulStop()
+	}, nil
 }
 
-// Addr returns the bound address.
+// ControlPlane: Negotiate (merge host views)
-func (s *GRPCServer) Addr() string {
+func (s *cartActorGRPCServer) Negotiate(ctx context.Context, req *messages.NegotiateRequest) (*messages.NegotiateReply, error) {
-	if s == nil {
+	hostSet := make(map[string]struct{})
-		return ""
+	// Caller view
+	for _, h := range req.GetKnownHosts() {
+		if h != "" {
+			hostSet[h] = struct{}{}
+		}
 	}
-	return s.addr
+	// This host
+	hostSet[s.syncedPool.Hostname] = struct{}{}
+	// Known remotes
+	s.syncedPool.mu.RLock()
+	for h := range s.syncedPool.remoteHosts {
+		hostSet[h] = struct{}{}
+	}
+	s.syncedPool.mu.RUnlock()
+
+	out := make([]string, 0, len(hostSet))
+	for h := range hostSet {
+		out = append(out, h)
+	}
+	return &messages.NegotiateReply{Hosts: out}, nil
 }
 
-// -----------------------------------------------------------------------------
+// ControlPlane: GetCartIds (locally owned carts only)
-// Client Dial Helpers (used later by refactored remote grain + control plane)
+func (s *cartActorGRPCServer) GetCartIds(ctx context.Context, _ *messages.Empty) (*messages.CartIdsReply, error) {
-// -----------------------------------------------------------------------------
+	s.syncedPool.local.mu.RLock()
-
+	ids := make([]string, 0, len(s.syncedPool.local.grains))
-// DialRemote establishes (or reuses externally) a gRPC client connection.
+	for _, g := range s.syncedPool.local.grains {
-func DialRemote(ctx context.Context, target string, opts ...grpc.DialOption) (*grpc.ClientConn, error) {
+		if g == nil {
-	dialOpts := []grpc.DialOption{
+			continue
-		grpc.WithInsecure(), // NOTE: Intentional for initial migration; replace with TLS / mTLS later.
+		}
-		grpc.WithBlock(),
+		ids = append(ids, g.GetId().String())
 	}
-	dialOpts = append(dialOpts, opts...)
+	s.syncedPool.local.mu.RUnlock()
-	ctxDial, cancel := context.WithTimeout(ctx, 5*time.Second)
+	return &messages.CartIdsReply{CartIds: ids}, nil
-	defer cancel()
+}
-	conn, err := grpc.DialContext(ctxDial, target, dialOpts...)
+
+// ControlPlane: Closing (peer shutdown notification)
+func (s *cartActorGRPCServer) Closing(ctx context.Context, req *messages.ClosingNotice) (*messages.OwnerChangeAck, error) {
+	if req.GetHost() != "" {
+		s.syncedPool.RemoveHost(req.GetHost())
+	}
+	return &messages.OwnerChangeAck{
+		Accepted: true,
+		Message:  "removed host",
+	}, nil
+}
+
+// StartGRPCServer configures and starts the unified gRPC server on the given address.
+// It registers both the CartActor and ControlPlane services.
+func StartGRPCServer(addr string, pool GrainPool, syncedPool *SyncedPool) (*grpc.Server, error) {
+	lis, err := net.Listen("tcp", addr)
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("failed to listen: %w", err)
 	}
-	return conn, nil
-}
 
-// -----------------------------------------------------------------------------
+	grpcServer := grpc.NewServer()
-// Utility for converting internal errors to gRPC status (if needed later).
+	server := NewCartActorGRPCServer(pool, syncedPool)
-// -----------------------------------------------------------------------------
 
-func grpcError(err error) error {
+	messages.RegisterCartActorServer(grpcServer, server)
-	if err == nil {
+	messages.RegisterControlPlaneServer(grpcServer, server)
-		return nil
+	reflection.Register(grpcServer)
-	}
+
-	// Extend mapping if we add richer error types.
+	log.Printf("gRPC server listening on %s", addr)
-	return status.Error(codes.Internal, err.Error())
+	go func() {
+		if err := grpcServer.Serve(lis); err != nil {
+			log.Fatalf("failed to serve gRPC: %v", err)
+		}
+	}()
+
+	return grpcServer, nil
 }

main.go

@@ -38,13 +38,13 @@ var (
 func spawn(id CartId) (*CartGrain, error) {
 	grainSpawns.Inc()
 	ret := &CartGrain{
-		lastItemId:      0,
+		lastItemId:     0,
-		lastDeliveryId:  0,
+		lastDeliveryId: 0,
-		Deliveries:      []*CartDelivery{},
+		Deliveries:     []*CartDelivery{},
-		Id:              id,
+		Id:             id,
-		Items:           []*CartItem{},
+		Items:          []*CartItem{},
-		storageMessages: []Message{},
+		// storageMessages removed (legacy event log deprecated)
-		TotalPrice:      0,
+		TotalPrice: 0,
 	}
 	err := loadMessages(ret, id)
 	return ret, err
@@ -97,23 +97,6 @@ var name = os.Getenv("POD_NAME")
 var amqpUrl = os.Getenv("AMQP_URL")
 var KlarnaInstance = NewKlarnaClient(KlarnaPlaygroundUrl, os.Getenv("KLARNA_API_USERNAME"), os.Getenv("KLARNA_API_PASSWORD"))
 
-func GetDiscovery() Discovery {
-	if podIp == "" {
-		return nil
-	}
-
-	config, kerr := rest.InClusterConfig()
-
-	if kerr != nil {
-		log.Fatalf("Error creating kubernetes client: %v\n", kerr)
-	}
-	client, err := kubernetes.NewForConfig(config)
-	if err != nil {
-		log.Fatalf("Error creating client: %v\n", err)
-	}
-	return NewK8sDiscovery(client)
-}
-
 var tpl = `<!DOCTYPE html>
 <html lang="en">
   <head>
@@ -153,6 +136,23 @@ func getCheckoutOrder(host string, cartId CartId) *messages.CreateCheckoutOrder
 	}
 }
 
+func GetDiscovery() Discovery {
+	if podIp == "" {
+		return nil
+	}
+
+	config, kerr := rest.InClusterConfig()
+
+	if kerr != nil {
+		log.Fatalf("Error creating kubernetes client: %v\n", kerr)
+	}
+	client, err := kubernetes.NewForConfig(config)
+	if err != nil {
+		log.Fatalf("Error creating client: %v\n", err)
+	}
+	return NewK8sDiscovery(client)
+}
+
 func main() {
 
 	storage, err := NewDiskStorage(fmt.Sprintf("data/%s_state.gob", name))
@@ -249,28 +249,20 @@ func main() {
 				return
 			}
 			cartId := ToCartId(cookie.Value)
-			reply, err := syncedServer.pool.Process(cartId, Message{
+			order, err = syncedServer.CreateOrUpdateCheckout(r.Host, cartId)
-				Type:    CreateCheckoutOrderType,
-				Content: getCheckoutOrder(r.Host, cartId),
-			})
 			if err != nil {
 				w.WriteHeader(http.StatusInternalServerError)
 				w.Write([]byte(err.Error()))
 			}
-			err = json.Unmarshal(reply.Payload, &order)
+			// v2: Apply now returns *CartGrain; order creation handled inside grain (no payload to unmarshal)
-			if err != nil {
-				w.WriteHeader(http.StatusInternalServerError)
-				w.Write([]byte(err.Error()))
-				return
-			}
 		} else {
-			prevOrder, err := KlarnaInstance.GetOrder(orderId)
+			order, err = KlarnaInstance.GetOrder(orderId)
 			if err != nil {
 				w.WriteHeader(http.StatusBadRequest)
 				w.Write([]byte(err.Error()))
 				return
 			}
-			order = prevOrder
+
 		}
 		w.Header().Set("Content-Type", "text/html; charset=utf-8")
 		w.Header().Set("Permissions-Policy", "payment=(self \"https://js.stripe.com\" \"https://m.stripe.network\" \"https://js.playground.kustom.co\")")
@@ -392,12 +384,9 @@ func main() {
 }
 
 func triggerOrderCompleted(err error, syncedServer *PoolServer, order *CheckoutOrder) error {
-	_, err = syncedServer.pool.Process(ToCartId(order.MerchantReference1), Message{
+	_, err = syncedServer.pool.Apply(ToCartId(order.MerchantReference1), &messages.OrderCreated{
-		Type: OrderCompletedType,
+		OrderId: order.ID,
-		Content: &messages.OrderCreated{
+		Status:  order.Status,
-			OrderId: order.ID,
-			Status:  order.Status,
-		},
 	})
 	return err
 }

message-handler.go

@@ -1,315 +0,0 @@
-package main
-
-import (
-	"fmt"
-	"io"
-
-	messages "git.tornberg.me/go-cart-actor/proto"
-	"google.golang.org/protobuf/proto"
-)
-
-var Handlers = map[uint16]MessageHandler{
-	AddRequestType:          &AddRequestHandler{},
-	AddItemType:             &AddItemHandler{},
-	ChangeQuantityType:      &ChangeQuantityHandler{},
-	SetDeliveryType:         &SetDeliveryHandler{},
-	RemoveItemType:          &RemoveItemHandler{},
-	RemoveDeliveryType:      &RemoveDeliveryHandler{},
-	CreateCheckoutOrderType: &CheckoutHandler{},
-	SetCartItemsType:        &SetCartItemsHandler{},
-	OrderCompletedType:      &OrderCompletedHandler{},
-}
-
-func GetMessageHandler(t uint16) (MessageHandler, error) {
-	h, ok := Handlers[t]
-	if !ok {
-		return nil, fmt.Errorf("no handler for message type %d", t)
-	}
-	return h, nil
-}
-
-type MessageHandler interface {
-	Write(*Message, io.Writer) error
-	Read(data []byte) (interface{}, error)
-	Is(*Message) bool
-}
-type TypedMessageHandler struct {
-	Type uint16
-}
-
-type SetCartItemsHandler struct {
-	TypedMessageHandler
-}
-
-func (h *SetCartItemsHandler) Write(m *Message, w io.Writer) error {
-	messageBytes, err := proto.Marshal(m.Content.(*messages.SetCartRequest))
-	if err != nil {
-		return err
-	}
-	w.Write(messageBytes)
-	return nil
-}
-
-func (h *SetCartItemsHandler) Read(data []byte) (interface{}, error) {
-	msg := &messages.SetCartRequest{}
-
-	err := proto.Unmarshal(data, msg)
-	if err != nil {
-		return nil, err
-	}
-	return msg, nil
-}
-
-func (h *SetCartItemsHandler) Is(m *Message) bool {
-	if m.Type != AddRequestType {
-		return false
-	}
-	_, ok := m.Content.(*messages.SetCartRequest)
-	return ok
-}
-
-type AddRequestHandler struct {
-	TypedMessageHandler
-}
-
-func (h *AddRequestHandler) Write(m *Message, w io.Writer) error {
-	messageBytes, err := proto.Marshal(m.Content.(*messages.AddRequest))
-	if err != nil {
-		return err
-	}
-	w.Write(messageBytes)
-	return nil
-}
-
-func (h *AddRequestHandler) Read(data []byte) (interface{}, error) {
-	msg := &messages.AddRequest{}
-
-	err := proto.Unmarshal(data, msg)
-	if err != nil {
-		return nil, err
-	}
-	return msg, nil
-}
-
-func (h *AddRequestHandler) Is(m *Message) bool {
-	if m.Type != AddRequestType {
-		return false
-	}
-	_, ok := m.Content.(*messages.AddRequest)
-	return ok
-}
-
-type AddItemHandler struct {
-	TypedMessageHandler
-}
-
-func (h *AddItemHandler) Write(m *Message, w io.Writer) error {
-	messageBytes, err := proto.Marshal(m.Content.(*messages.AddItem))
-	if err != nil {
-		return err
-	}
-	w.Write(messageBytes)
-	return nil
-}
-
-func (h *AddItemHandler) Read(data []byte) (interface{}, error) {
-	msg := &messages.AddItem{}
-
-	err := proto.Unmarshal(data, msg)
-	if err != nil {
-		return nil, err
-	}
-	return msg, nil
-}
-
-func (h *AddItemHandler) Is(m *Message) bool {
-	if m.Type != AddItemType {
-		return false
-	}
-	_, ok := m.Content.(*messages.AddItem)
-	return ok
-}
-
-type ChangeQuantityHandler struct {
-	TypedMessageHandler
-}
-
-func (h *ChangeQuantityHandler) Write(m *Message, w io.Writer) error {
-	messageBytes, err := proto.Marshal(m.Content.(*messages.ChangeQuantity))
-	if err != nil {
-		return err
-	}
-	w.Write(messageBytes)
-	return nil
-}
-
-func (h *ChangeQuantityHandler) Read(data []byte) (interface{}, error) {
-	msg := &messages.ChangeQuantity{}
-
-	err := proto.Unmarshal(data, msg)
-	if err != nil {
-		return nil, err
-	}
-	return msg, nil
-}
-
-func (h *ChangeQuantityHandler) Is(m *Message) bool {
-	if m.Type != ChangeQuantityType {
-		return false
-	}
-	_, ok := m.Content.(*messages.ChangeQuantity)
-	return ok
-}
-
-type SetDeliveryHandler struct {
-	TypedMessageHandler
-}
-
-func (h *SetDeliveryHandler) Write(m *Message, w io.Writer) error {
-	messageBytes, err := proto.Marshal(m.Content.(*messages.SetDelivery))
-	if err != nil {
-		return err
-	}
-	w.Write(messageBytes)
-	return nil
-}
-
-func (h *SetDeliveryHandler) Read(data []byte) (interface{}, error) {
-	msg := &messages.SetDelivery{}
-
-	err := proto.Unmarshal(data, msg)
-	if err != nil {
-		return nil, err
-	}
-	return msg, nil
-}
-
-func (h *SetDeliveryHandler) Is(m *Message) bool {
-	if m.Type != ChangeQuantityType {
-		return false
-	}
-	_, ok := m.Content.(*messages.SetDelivery)
-	return ok
-}
-
-type RemoveItemHandler struct {
-	TypedMessageHandler
-}
-
-func (h *RemoveItemHandler) Write(m *Message, w io.Writer) error {
-	messageBytes, err := proto.Marshal(m.Content.(*messages.RemoveItem))
-	if err != nil {
-		return err
-	}
-	w.Write(messageBytes)
-	return nil
-}
-
-func (h *RemoveItemHandler) Read(data []byte) (interface{}, error) {
-	msg := &messages.RemoveItem{}
-
-	err := proto.Unmarshal(data, msg)
-	if err != nil {
-		return nil, err
-	}
-	return msg, nil
-}
-
-func (h *RemoveItemHandler) Is(m *Message) bool {
-	if m.Type != AddItemType {
-		return false
-	}
-	_, ok := m.Content.(*messages.RemoveItem)
-	return ok
-}
-
-type RemoveDeliveryHandler struct {
-	TypedMessageHandler
-}
-
-func (h *RemoveDeliveryHandler) Write(m *Message, w io.Writer) error {
-	messageBytes, err := proto.Marshal(m.Content.(*messages.RemoveDelivery))
-	if err != nil {
-		return err
-	}
-	w.Write(messageBytes)
-	return nil
-}
-
-func (h *RemoveDeliveryHandler) Read(data []byte) (interface{}, error) {
-	msg := &messages.RemoveDelivery{}
-
-	err := proto.Unmarshal(data, msg)
-	if err != nil {
-		return nil, err
-	}
-	return msg, nil
-}
-
-func (h *RemoveDeliveryHandler) Is(m *Message) bool {
-	if m.Type != AddItemType {
-		return false
-	}
-	_, ok := m.Content.(*messages.RemoveDelivery)
-	return ok
-}
-
-type CheckoutHandler struct {
-	TypedMessageHandler
-}
-
-func (h *CheckoutHandler) Write(m *Message, w io.Writer) error {
-	messageBytes, err := proto.Marshal(m.Content.(*messages.CreateCheckoutOrder))
-	if err != nil {
-		return err
-	}
-	w.Write(messageBytes)
-	return nil
-}
-
-func (h *CheckoutHandler) Read(data []byte) (interface{}, error) {
-	msg := &messages.CreateCheckoutOrder{}
-
-	err := proto.Unmarshal(data, msg)
-	if err != nil {
-		return nil, err
-	}
-	return msg, nil
-}
-
-func (h *CheckoutHandler) Is(m *Message) bool {
-	if m.Type != CreateCheckoutOrderType {
-		return false
-	}
-	_, ok := m.Content.(*messages.CreateCheckoutOrder)
-	return ok
-}
-
-type OrderCompletedHandler struct {
-	TypedMessageHandler
-}
-
-func (h *OrderCompletedHandler) Write(m *Message, w io.Writer) error {
-	messageBytes, err := proto.Marshal(m.Content.(*messages.OrderCreated))
-	if err != nil {
-		return err
-	}
-	w.Write(messageBytes)
-	return nil
-}
-func (h *OrderCompletedHandler) Read(data []byte) (interface{}, error) {
-	msg := &messages.OrderCreated{}
-
-	err := proto.Unmarshal(data, msg)
-	if err != nil {
-		return nil, err
-	}
-	return msg, nil
-}
-func (h *OrderCompletedHandler) Is(m *Message) bool {
-	if m.Type != OrderCompletedType {
-		return false
-	}
-	_, ok := m.Content.(*messages.OrderCreated)
-	return ok
-}

message-types.go

@@ -1,15 +0,0 @@
-package main
-
-const (
-	AddRequestType = 1
-	AddItemType    = 2
-
-	RemoveItemType          = 4
-	RemoveDeliveryType      = 5
-	ChangeQuantityType      = 6
-	SetDeliveryType         = 7
-	SetPickupPointType      = 8
-	CreateCheckoutOrderType = 9
-	SetCartItemsType        = 10
-	OrderCompletedType      = 11
-)

message.go

@@ -1,94 +0,0 @@
-package main
-
-import (
-	"bytes"
-	"encoding/binary"
-	"io"
-	"time"
-)
-
-type StorableMessage interface {
-	Write(w io.Writer) error
-}
-
-type Message struct {
-	Type      uint16
-	TimeStamp *int64
-	Content   interface{}
-}
-
-type MessageWriter struct {
-	io.Writer
-}
-
-type StorableMessageHeader struct {
-	Version    uint16
-	Type       uint16
-	TimeStamp  int64
-	DataLength uint64
-}
-
-func GetData(fn func(w io.Writer) error) ([]byte, error) {
-	var buf bytes.Buffer
-	err := fn(&buf)
-	if err != nil {
-		return nil, err
-	}
-	b := buf.Bytes()
-	return b, nil
-}
-
-func (m Message) Write(w io.Writer) error {
-	h, err := GetMessageHandler(m.Type)
-	if err != nil {
-		return err
-	}
-	data, err := GetData(func(w io.Writer) error {
-		return h.Write(&m, w)
-	})
-	if err != nil {
-		return err
-	}
-	ts := time.Now().Unix()
-	if m.TimeStamp != nil {
-		ts = *m.TimeStamp
-	}
-
-	err = binary.Write(w, binary.LittleEndian, StorableMessageHeader{
-		Version:    1,
-		Type:       m.Type,
-		TimeStamp:  ts,
-		DataLength: uint64(len(data)),
-	})
-	w.Write(data)
-
-	return err
-}
-
-func ReadMessage(reader io.Reader, m *Message) error {
-
-	header := StorableMessageHeader{}
-	err := binary.Read(reader, binary.LittleEndian, &header)
-	if err != nil {
-		return err
-	}
-	messageBytes := make([]byte, header.DataLength)
-	_, err = reader.Read(messageBytes)
-	if err != nil {
-		return err
-	}
-	h, err := GetMessageHandler(header.Type)
-	if err != nil {
-		return err
-	}
-	content, err := h.Read(messageBytes)
-	if err != nil {
-		return err
-	}
-	m.Content = content
-
-	m.Type = header.Type
-	m.TimeStamp = &header.TimeStamp
-
-	return nil
-}

multi_node_ownership_test.go

@@ -0,0 +1,182 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"testing"
+	"time"
+
+	messages "git.tornberg.me/go-cart-actor/proto"
+	"google.golang.org/grpc"
+)
+
+// TestMultiNodeOwnershipNegotiation spins up two gRPC servers (nodeA, nodeB),
+// manually links their SyncedPools (bypassing AddRemote's fixed port assumption),
+// and verifies that only one node becomes the owner of a new cart while the
+// other can still apply a mutation via the remote proxy path.
+//
+// NOTE:
+//   - We manually inject RemoteHostGRPC entries because AddRemote() hard-codes
+//     port 1337; to run two distinct servers concurrently we need distinct ports.
+//   - This test asserts single ownership consistency rather than the complete
+//     quorum semantics (which depend on real discovery + AddRemote).
+func TestMultiNodeOwnershipNegotiation(t *testing.T) {
+	// Allocate distinct ports for the two nodes.
+	const (
+		addrA = "127.0.0.1:18081"
+		addrB = "127.0.0.1:18082"
+		hostA = "nodeA"
+		hostB = "nodeB"
+	)
+
+	// Create local grain pools.
+	poolA := NewGrainLocalPool(1024, time.Minute, spawn)
+	poolB := NewGrainLocalPool(1024, time.Minute, spawn)
+
+	// Create synced pools (no discovery).
+	syncedA, err := NewSyncedPool(poolA, hostA, nil)
+	if err != nil {
+		t.Fatalf("nodeA NewSyncedPool error: %v", err)
+	}
+	syncedB, err := NewSyncedPool(poolB, hostB, nil)
+	if err != nil {
+		t.Fatalf("nodeB NewSyncedPool error: %v", err)
+	}
+
+	// Start gRPC servers (CartActor + ControlPlane) on different ports.
+	grpcSrvA, err := StartGRPCServer(addrA, poolA, syncedA)
+	if err != nil {
+		t.Fatalf("StartGRPCServer A error: %v", err)
+	}
+	defer grpcSrvA.GracefulStop()
+
+	grpcSrvB, err := StartGRPCServer(addrB, poolB, syncedB)
+	if err != nil {
+		t.Fatalf("StartGRPCServer B error: %v", err)
+	}
+	defer grpcSrvB.GracefulStop()
+
+	// Helper to connect one pool to the other's server (manual AddRemote equivalent).
+	link := func(src *SyncedPool, remoteHost, remoteAddr string) {
+		ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
+		defer cancel()
+		conn, dialErr := grpc.DialContext(ctx, remoteAddr, grpc.WithInsecure(), grpc.WithBlock())
+		if dialErr != nil {
+			t.Fatalf("dial %s (%s) failed: %v", remoteHost, remoteAddr, dialErr)
+		}
+		cartClient := messages.NewCartActorClient(conn)
+		controlClient := messages.NewControlPlaneClient(conn)
+
+		src.mu.Lock()
+		src.remoteHosts[remoteHost] = &RemoteHostGRPC{
+			Host:          remoteHost,
+			Conn:          conn,
+			CartClient:    cartClient,
+			ControlClient: controlClient,
+		}
+		src.mu.Unlock()
+	}
+
+	// Cross-link the two pools.
+	link(syncedA, hostB, addrB)
+	link(syncedB, hostA, addrA)
+
+	// Rebuild rings after manual cross-link so deterministic ownership works immediately.
+	syncedA.ForceRingRefresh()
+	syncedB.ForceRingRefresh()
+
+	// Allow brief stabilization (control plane pings / no real negotiation needed here).
+	time.Sleep(200 * time.Millisecond)
+
+	// Create a deterministic cart id for test readability.
+	cartID := ToCartId(fmt.Sprintf("cart-%d", time.Now().UnixNano()))
+
+	// Mutation payload (ring-determined ownership; no assumption about which node owns).
+	addItem := &messages.AddItem{
+		ItemId:   1,
+		Quantity: 1,
+		Price:    1500,
+		OrgPrice: 1500,
+		Sku:      "sku-test-multi",
+		Name:     "Multi Node Test",
+		Image:    "/test.png",
+		Stock:    2,
+		Tax:      2500,
+		Country:  "se",
+	}
+
+	// Determine ring owner and set primary / secondary references.
+	ownerHost := syncedA.DebugOwnerHost(cartID)
+	var ownerSynced, otherSynced *SyncedPool
+	var ownerPool, otherPool *GrainLocalPool
+	switch ownerHost {
+	case hostA:
+		ownerSynced, ownerPool = syncedA, poolA
+		otherSynced, otherPool = syncedB, poolB
+	case hostB:
+		ownerSynced, ownerPool = syncedB, poolB
+		otherSynced, otherPool = syncedA, poolA
+	default:
+		t.Fatalf("unexpected ring owner %s (expected %s or %s)", ownerHost, hostA, hostB)
+	}
+
+	// Apply mutation on the ring-designated owner.
+	if _, err := ownerSynced.Apply(cartID, addItem); err != nil {
+		t.Fatalf("owner %s Apply addItem error: %v", ownerHost, err)
+	}
+
+	// Validate owner pool has the grain and the other does not.
+	if _, ok := ownerPool.GetGrains()[cartID]; !ok {
+		t.Fatalf("expected owner %s to have local grain", ownerHost)
+	}
+	if _, ok := otherPool.GetGrains()[cartID]; ok {
+		t.Fatalf("non-owner unexpectedly holds local grain")
+	}
+
+	// Prepare change mutation to be applied from the non-owner (should route remotely).
+	change := &messages.ChangeQuantity{
+		Id:       1, // line id after first AddItem
+		Quantity: 2,
+	}
+	// Apply remotely via the non-owner.
+	if _, err := otherSynced.Apply(cartID, change); err != nil {
+		t.Fatalf("non-owner remote Apply changeQuantity error: %v", err)
+	}
+
+	// Remote re-mutation already performed via otherSynced; removed duplicate block.
+
+	// NodeB local grain assertion:
+	// Only assert absence if nodeB is NOT the ring-designated owner. If nodeB is the owner,
+	// it is expected to have a local grain (previous generic ownership assertions already ran).
+	if ownerHost != hostB {
+		if _, local := poolB.GetGrains()[cartID]; local {
+			t.Fatalf("nodeB unexpectedly created local grain (ownership duplication)")
+		}
+	}
+
+	// Fetch state from nodeB to ensure we see updated quantity (2).
+	grainStateB, err := syncedB.Get(cartID)
+	if err != nil {
+		t.Fatalf("nodeB Get error: %v", err)
+	}
+	if len(grainStateB.Items) != 1 || grainStateB.Items[0].Quantity != 2 {
+		t.Fatalf("nodeB observed inconsistent state: items=%d qty=%d (expected 1 / 2)",
+			len(grainStateB.Items),
+			func() int {
+				if len(grainStateB.Items) == 0 {
+					return -1
+				}
+				return grainStateB.Items[0].Quantity
+			}(),
+		)
+	}
+
+	// Cross-check from nodeA (authoritative) to ensure state matches.
+	grainStateA, err := syncedA.Get(cartID)
+	if err != nil {
+		t.Fatalf("nodeA Get error: %v", err)
+	}
+	if grainStateA.Items[0].Quantity != 2 {
+		t.Fatalf("nodeA authoritative state mismatch: expected qty=2 got %d", grainStateA.Items[0].Quantity)
+	}
+}

multi_node_three_test.go

@@ -0,0 +1,304 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"testing"
+	"time"
+
+	messages "git.tornberg.me/go-cart-actor/proto"
+	"google.golang.org/grpc"
+)
+
+// TestThreeNodeMajorityOwnership validates ring-determined ownership and routing
+// in a 3-node cluster (A,B,C) using the consistent hashing ring (no quorum RPC).
+// The previous ConfirmOwner / quorum semantics have been removed; ownership is
+// deterministic and derived from the ring.
+//
+// It validates:
+//  1. The ring selects exactly one primary owner for a new cart.
+//  2. Other nodes (B,C) do NOT create local grains for the cart.
+//  3. Remote proxies are installed lazily so remote mutations can route.
+//  4. A remote mutation from one non-owner updates state visible on another.
+//  5. Authoritative state on the owner matches remote observations.
+//  6. (Future) This scaffolds replication tests when RF>1 is enabled.
+//
+// (Legacy comments about ConfirmOwner acceptance thresholds have been removed.)
+// (Function name retained for historical continuity.)
+func TestThreeNodeMajorityOwnership(t *testing.T) {
+	const (
+		addrA = "127.0.0.1:18181"
+		addrB = "127.0.0.1:18182"
+		addrC = "127.0.0.1:18183"
+		hostA = "nodeA3"
+		hostB = "nodeB3"
+		hostC = "nodeC3"
+	)
+
+	// Local grain pools
+	poolA := NewGrainLocalPool(1024, time.Minute, spawn)
+	poolB := NewGrainLocalPool(1024, time.Minute, spawn)
+	poolC := NewGrainLocalPool(1024, time.Minute, spawn)
+
+	// Synced pools (no discovery)
+	syncedA, err := NewSyncedPool(poolA, hostA, nil)
+	if err != nil {
+		t.Fatalf("nodeA NewSyncedPool error: %v", err)
+	}
+	syncedB, err := NewSyncedPool(poolB, hostB, nil)
+	if err != nil {
+		t.Fatalf("nodeB NewSyncedPool error: %v", err)
+	}
+	syncedC, err := NewSyncedPool(poolC, hostC, nil)
+	if err != nil {
+		t.Fatalf("nodeC NewSyncedPool error: %v", err)
+	}
+
+	// Start gRPC servers
+	grpcSrvA, err := StartGRPCServer(addrA, poolA, syncedA)
+	if err != nil {
+		t.Fatalf("StartGRPCServer A error: %v", err)
+	}
+	defer grpcSrvA.GracefulStop()
+	grpcSrvB, err := StartGRPCServer(addrB, poolB, syncedB)
+	if err != nil {
+		t.Fatalf("StartGRPCServer B error: %v", err)
+	}
+	defer grpcSrvB.GracefulStop()
+	grpcSrvC, err := StartGRPCServer(addrC, poolC, syncedC)
+	if err != nil {
+		t.Fatalf("StartGRPCServer C error: %v", err)
+	}
+	defer grpcSrvC.GracefulStop()
+
+	// Helper for manual cross-link (since AddRemote assumes fixed port)
+	link := func(src *SyncedPool, remoteHost, remoteAddr string) {
+		ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
+		defer cancel()
+		conn, dialErr := grpc.DialContext(ctx, remoteAddr, grpc.WithInsecure(), grpc.WithBlock())
+		if dialErr != nil {
+			t.Fatalf("dial %s (%s) failed: %v", remoteHost, remoteAddr, dialErr)
+		}
+		cartClient := messages.NewCartActorClient(conn)
+		controlClient := messages.NewControlPlaneClient(conn)
+
+		src.mu.Lock()
+		src.remoteHosts[remoteHost] = &RemoteHostGRPC{
+			Host:          remoteHost,
+			Conn:          conn,
+			CartClient:    cartClient,
+			ControlClient: controlClient,
+		}
+		src.mu.Unlock()
+	}
+
+	// Full mesh (each node knows all others)
+	link(syncedA, hostB, addrB)
+	link(syncedA, hostC, addrC)
+
+	link(syncedB, hostA, addrA)
+	link(syncedB, hostC, addrC)
+
+	link(syncedC, hostA, addrA)
+	link(syncedC, hostB, addrB)
+
+	// Rebuild rings after manual linking so ownership resolution is immediate.
+	syncedA.ForceRingRefresh()
+	syncedB.ForceRingRefresh()
+	syncedC.ForceRingRefresh()
+
+	// Allow brief stabilization
+	time.Sleep(200 * time.Millisecond)
+
+	// Deterministic-ish cart id
+	cartID := ToCartId(fmt.Sprintf("cart3-%d", time.Now().UnixNano()))
+
+	addItem := &messages.AddItem{
+		ItemId:   10,
+		Quantity: 1,
+		Price:    5000,
+		OrgPrice: 5000,
+		Sku:      "sku-3node",
+		Name:     "Three Node Test",
+		Image:    "/t.png",
+		Stock:    10,
+		Tax:      2500,
+		Country:  "se",
+	}
+
+	// Determine ring-designated owner (may be any of the three hosts)
+	ownerPre := syncedA.DebugOwnerHost(cartID)
+	if ownerPre != hostA && ownerPre != hostB && ownerPre != hostC {
+		t.Fatalf("ring returned unexpected owner %s (not in set {%s,%s,%s})", ownerPre, hostA, hostB, hostC)
+	}
+	var ownerSynced *SyncedPool
+	var ownerPool *GrainLocalPool
+	switch ownerPre {
+	case hostA:
+		ownerSynced, ownerPool = syncedA, poolA
+	case hostB:
+		ownerSynced, ownerPool = syncedB, poolB
+	case hostC:
+		ownerSynced, ownerPool = syncedC, poolC
+	}
+	// Pick two distinct non-owner nodes for remote mutation assertions
+	var remote1Synced, remote2Synced *SyncedPool
+	switch ownerPre {
+	case hostA:
+		remote1Synced, remote2Synced = syncedB, syncedC
+	case hostB:
+		remote1Synced, remote2Synced = syncedA, syncedC
+	case hostC:
+		remote1Synced, remote2Synced = syncedA, syncedB
+	}
+
+	// Apply on the ring-designated owner
+	if _, err := ownerSynced.Apply(cartID, addItem); err != nil {
+		t.Fatalf("owner %s Apply addItem error: %v", ownerPre, err)
+	}
+
+	// Small wait for remote proxy spawn (ring ownership already deterministic)
+	time.Sleep(150 * time.Millisecond)
+
+	// Assert only nodeA has local grain
+	localCount := 0
+	if _, ok := poolA.GetGrains()[cartID]; ok {
+		localCount++
+	}
+	if _, ok := poolB.GetGrains()[cartID]; ok {
+		localCount++
+	}
+	if _, ok := poolC.GetGrains()[cartID]; ok {
+		localCount++
+	}
+	if localCount != 1 {
+		t.Fatalf("expected exactly 1 local grain, got %d", localCount)
+	}
+	if _, ok := ownerPool.GetGrains()[cartID]; !ok {
+		t.Fatalf("expected owner %s to hold local grain", ownerPre)
+	}
+
+	// Remote proxies may not pre-exist; first remote mutation will trigger SpawnRemoteGrain lazily.
+
+	// Issue remote mutation from one non-owner -> ChangeQuantity (increase)
+	change := &messages.ChangeQuantity{
+		Id:       1,
+		Quantity: 3,
+	}
+	if _, err := remote1Synced.Apply(cartID, change); err != nil {
+		t.Fatalf("remote mutation (remote1) changeQuantity error: %v", err)
+	}
+
+	// Validate updated state visible via nodeC
+	stateC, err := remote2Synced.Get(cartID)
+	if err != nil {
+		t.Fatalf("nodeC Get error: %v", err)
+	}
+	if len(stateC.Items) != 1 || stateC.Items[0].Quantity != 3 {
+		t.Fatalf("nodeC observed state mismatch: items=%d qty=%d (expected 1 / 3)",
+			len(stateC.Items),
+			func() int {
+				if len(stateC.Items) == 0 {
+					return -1
+				}
+				return stateC.Items[0].Quantity
+			}(),
+		)
+	}
+
+	// Cross-check authoritative nodeA
+	stateA, err := syncedA.Get(cartID)
+	if err != nil {
+		t.Fatalf("nodeA Get error: %v", err)
+	}
+	if stateA.Items[0].Quantity != 3 {
+		t.Fatalf("nodeA authoritative state mismatch: expected qty=3 got %d", stateA.Items[0].Quantity)
+	}
+}
+
+// TestThreeNodeDiscoveryMajorityOwnership (placeholder)
+// This test is a scaffold demonstrating how a MockDiscovery would be wired
+// once AddRemote supports host:port (currently hard-coded to :1337).
+// It is skipped to avoid flakiness / false negatives until the production
+// AddRemote logic is enhanced to parse dynamic ports or the test harness
+// provides consistent port mapping.
+func TestThreeNodeDiscoveryMajorityOwnership(t *testing.T) {
+	t.Skip("Pending enhancement: AddRemote needs host:port support to fully exercise discovery-based multi-node linking")
+	// Example skeleton (non-functional with current AddRemote implementation):
+	//
+	// md := NewMockDiscovery([]string{"nodeB3", "nodeC3"})
+	// poolA := NewGrainLocalPool(1024, time.Minute, spawn)
+	// syncedA, err := NewSyncedPool(poolA, "nodeA3", md)
+	// if err != nil {
+	//     t.Fatalf("NewSyncedPool with mock discovery error: %v", err)
+	// }
+	// // Start server for nodeA (would also need servers for nodeB3/nodeC3 on expected ports)
+	// // grpcSrvA, _ := StartGRPCServer(":1337", poolA, syncedA)
+	// // defer grpcSrvA.GracefulStop()
+	//
+	// // Dynamically add a host via discovery
+	// // md.AddHost("nodeB3")
+	// // time.Sleep(100 * time.Millisecond) // allow AddRemote attempt
+	//
+	// // Assertions would verify syncedA.remoteHosts contains "nodeB3"
+}
+
+// TestHostRemovalAndErrorWithMockDiscovery validates behavior when:
+// 1. Discovery reports a host that cannot be dialed (AddRemote error path)
+// 2. That host is then removed (Deleted event) without leaving residual state
+// 3. A second failing host is added afterward (ensuring watcher still processes events)
+//
+// NOTE: Because AddRemote currently hard-codes :1337 and we are NOT starting a
+// real server for the bogus hosts, the dial will fail and the remote host should
+// never appear in remoteHosts. This intentionally exercises the error logging
+// path: "AddRemote: dial ... failed".
+func TestHostRemovalAndErrorWithMockDiscovery(t *testing.T) {
+	// Start a real node A (acts as the observing node)
+	const addrA = "127.0.0.1:18281"
+	hostA := "nodeA-md"
+
+	poolA := NewGrainLocalPool(128, time.Minute, spawn)
+
+	// Mock discovery starts with one bogus host that will fail to connect.
+	md := NewMockDiscovery([]string{"bogus-host-1"})
+	syncedA, err := NewSyncedPool(poolA, hostA, md)
+	if err != nil {
+		t.Fatalf("NewSyncedPool error: %v", err)
+	}
+
+	grpcSrvA, err := StartGRPCServer(addrA, poolA, syncedA)
+	if err != nil {
+		t.Fatalf("StartGRPCServer A error: %v", err)
+	}
+	defer grpcSrvA.GracefulStop()
+
+	// Kick off watch processing by starting Watch() (NewSyncedPool does this internally
+	// when discovery is non-nil, but we ensure events channel is active).
+	// The initial bogus host should trigger AddRemote -> dial failure.
+	time.Sleep(300 * time.Millisecond)
+
+	syncedA.mu.RLock()
+	if len(syncedA.remoteHosts) != 0 {
+		syncedA.mu.RUnlock()
+		t.Fatalf("expected 0 remoteHosts after failing dial, got %d", len(syncedA.remoteHosts))
+	}
+	syncedA.mu.RUnlock()
+
+	// Remove the bogus host (should not panic; no entry to clean up).
+	md.RemoveHost("bogus-host-1")
+	time.Sleep(100 * time.Millisecond)
+
+	// Add another bogus host to ensure watcher still alive.
+	md.AddHost("bogus-host-2")
+	time.Sleep(300 * time.Millisecond)
+
+	syncedA.mu.RLock()
+	if len(syncedA.remoteHosts) != 0 {
+		syncedA.mu.RUnlock()
+		t.Fatalf("expected 0 remoteHosts after second failing dial, got %d", len(syncedA.remoteHosts))
+	}
+	syncedA.mu.RUnlock()
+
+	// Clean up discovery
+	md.Close()
+}

mutation_add_item.go

@@ -0,0 +1,82 @@
+package main
+
+import (
+	"fmt"
+
+	messages "git.tornberg.me/go-cart-actor/proto"
+)
+
+// mutation_add_item.go
+//
+// Registers the AddItem cart mutation in the generic mutation registry.
+// This replaces the legacy switch-based logic previously found in CartGrain.Apply.
+//
+// Behavior:
+//   * Validates quantity > 0
+//   * If an item with same SKU exists -> increases quantity
+//   * Else creates a new CartItem with computed tax amounts
+//   * Totals recalculated automatically via WithTotals()
+//
+// NOTE: Any future field additions in messages.AddItem that affect pricing / tax
+// must keep this handler in sync.
+
+func init() {
+	RegisterMutation[messages.AddItem](
+		"AddItem",
+		func(g *CartGrain, m *messages.AddItem) error {
+			if m == nil {
+				return fmt.Errorf("AddItem: nil payload")
+			}
+			if m.Quantity < 1 {
+				return fmt.Errorf("AddItem: invalid quantity %d", m.Quantity)
+			}
+
+			// Fast path: merge with existing item having same SKU
+			if existing, found := g.FindItemWithSku(m.Sku); found {
+				existing.Quantity += int(m.Quantity)
+				return nil
+			}
+
+			g.mu.Lock()
+			defer g.mu.Unlock()
+
+			g.lastItemId++
+			taxRate := 2500
+			if m.Tax > 0 {
+				taxRate = int(m.Tax)
+			}
+			taxAmountPerUnit := GetTaxAmount(m.Price, taxRate)
+
+			g.Items = append(g.Items, &CartItem{
+				Id:          g.lastItemId,
+				ItemId:      int(m.ItemId),
+				Quantity:    int(m.Quantity),
+				Sku:         m.Sku,
+				Name:        m.Name,
+				Price:       m.Price,
+				TotalPrice:  m.Price * int64(m.Quantity),
+				TotalTax:    int64(taxAmountPerUnit * int64(m.Quantity)),
+				Image:       m.Image,
+				Stock:       StockStatus(m.Stock),
+				Disclaimer:  m.Disclaimer,
+				Brand:       m.Brand,
+				Category:    m.Category,
+				Category2:   m.Category2,
+				Category3:   m.Category3,
+				Category4:   m.Category4,
+				Category5:   m.Category5,
+				OrgPrice:    m.OrgPrice,
+				ArticleType: m.ArticleType,
+				Outlet:      m.Outlet,
+				SellerId:    m.SellerId,
+				SellerName:  m.SellerName,
+				Tax:         int(taxAmountPerUnit),
+				TaxRate:     taxRate,
+				StoreId:     m.StoreId,
+			})
+
+			return nil
+		},
+		WithTotals(), // Recalculate totals after successful mutation
+	)
+}

mutation_add_request.go

@@ -0,0 +1,61 @@
+package main
+
+import (
+	"fmt"
+
+	messages "git.tornberg.me/go-cart-actor/proto"
+)
+
+// mutation_add_request.go
+//
+// Registers the AddRequest mutation. This mutation is a higher-level intent
+// (add by SKU + quantity) which may translate into either:
+//   - Increasing quantity of an existing line (same SKU), OR
+//   - Creating a new item by performing a product lookup (via getItemData inside CartGrain.AddItem)
+//
+// Behavior:
+//   - Validates non-empty SKU and quantity > 0
+//   - If an item with the SKU already exists: increments its quantity
+//   - Else delegates to CartGrain.AddItem (which itself produces an AddItem mutation)
+//   - Totals recalculated automatically (WithTotals)
+//
+// NOTE:
+//   - This handler purposely avoids duplicating the detailed AddItem logic;
+//     it reuses CartGrain.AddItem which then flows through the AddItem mutation
+//     registry handler.
+//   - Double total recalculation can occur (AddItem has WithTotals too), but
+//     is acceptable for clarity. Optimize later if needed.
+//
+// Potential future improvements:
+//   - Stock validation before increasing quantity
+//   - Reservation logic or concurrency guards around stock updates
+//   - Coupon / pricing rules applied conditionally during add-by-sku
+func init() {
+	RegisterMutation[messages.AddRequest](
+		"AddRequest",
+		func(g *CartGrain, m *messages.AddRequest) error {
+			if m == nil {
+				return fmt.Errorf("AddRequest: nil payload")
+			}
+			if m.Sku == "" {
+				return fmt.Errorf("AddRequest: sku is empty")
+			}
+			if m.Quantity < 1 {
+				return fmt.Errorf("AddRequest: invalid quantity %d", m.Quantity)
+			}
+
+			// Existing line: accumulate quantity only.
+			if existing, found := g.FindItemWithSku(m.Sku); found {
+				existing.Quantity += int(m.Quantity)
+				return nil
+			}
+
+			// New line: delegate to higher-level AddItem flow (product lookup).
+			// We intentionally ignore the returned *CartGrain; registry will
+			// do totals again after this handler returns (harmless).
+			_, err := g.AddItem(m.Sku, int(m.Quantity), m.Country, m.StoreId)
+			return err
+		},
+		WithTotals(),
+	)
+}

mutation_change_quantity.go

@@ -0,0 +1,58 @@
+package main
+
+import (
+	"fmt"
+
+	messages "git.tornberg.me/go-cart-actor/proto"
+)
+
+// mutation_change_quantity.go
+//
+// Registers the ChangeQuantity mutation.
+//
+// Behavior:
+//   - Locates an item by its cart-local line item Id (not source item_id).
+//   - If requested quantity <= 0 the line is removed.
+//   - Otherwise the line's Quantity field is updated.
+//   - Totals are recalculated (WithTotals).
+//
+// Error handling:
+//   - Returns an error if the item Id is not found.
+//   - Returns an error if payload is nil (defensive).
+//
+// Concurrency:
+//   - Uses the grain's RW-safe mutation pattern: we mutate in place under
+//     the grain's implicit expectation that higher layers control access.
+//     (If strict locking is required around every mutation, wrap logic in
+//     an explicit g.mu.Lock()/Unlock(), but current model mirrors prior code.)
+func init() {
+	RegisterMutation[messages.ChangeQuantity](
+		"ChangeQuantity",
+		func(g *CartGrain, m *messages.ChangeQuantity) error {
+			if m == nil {
+				return fmt.Errorf("ChangeQuantity: nil payload")
+			}
+
+			foundIndex := -1
+			for i, it := range g.Items {
+				if it.Id == int(m.Id) {
+					foundIndex = i
+					break
+				}
+			}
+			if foundIndex == -1 {
+				return fmt.Errorf("ChangeQuantity: item id %d not found", m.Id)
+			}
+
+			if m.Quantity <= 0 {
+				// Remove the item
+				g.Items = append(g.Items[:foundIndex], g.Items[foundIndex+1:]...)
+				return nil
+			}
+
+			g.Items[foundIndex].Quantity = int(m.Quantity)
+			return nil
+		},
+		WithTotals(),
+	)
+}

mutation_initialize_checkout.go

@@ -0,0 +1,49 @@
+package main
+
+import (
+	"fmt"
+
+	messages "git.tornberg.me/go-cart-actor/proto"
+)
+
+// mutation_initialize_checkout.go
+//
+// Registers the InitializeCheckout mutation.
+// This mutation is invoked AFTER an external Klarna checkout session
+// has been successfully created or updated. It persists the Klarna
+// order reference / status and marks the cart as having a payment in progress.
+//
+// Behavior:
+//   - Sets OrderReference to the Klarna order ID (overwriting if already set).
+//   - Sets PaymentStatus to the current Klarna status.
+//   - Sets / updates PaymentInProgress flag.
+//   - Does NOT alter pricing or line items (so no totals recalculation).
+//
+// Validation:
+//   - Returns an error if payload is nil.
+//   - Returns an error if orderId is empty (integrity guard).
+//
+// Concurrency:
+//   - Relies on upstream mutation serialization for a single grain. If
+//     parallel checkout attempts are possible, add higher-level guards
+//     (e.g. reject if PaymentInProgress already true unless reusing
+//     the same OrderReference).
+func init() {
+	RegisterMutation[messages.InitializeCheckout](
+		"InitializeCheckout",
+		func(g *CartGrain, m *messages.InitializeCheckout) error {
+			if m == nil {
+				return fmt.Errorf("InitializeCheckout: nil payload")
+			}
+			if m.OrderId == "" {
+				return fmt.Errorf("InitializeCheckout: missing orderId")
+			}
+
+			g.OrderReference = m.OrderId
+			g.PaymentStatus = m.Status
+			g.PaymentInProgress = m.PaymentInProgress
+			return nil
+		},
+		// No WithTotals(): monetary aggregates are unaffected.
+	)
+}

mutation_order_created.go

@@ -0,0 +1,53 @@
+package main
+
+import (
+	"fmt"
+
+	messages "git.tornberg.me/go-cart-actor/proto"
+)
+
+// mutation_order_created.go
+//
+// Registers the OrderCreated mutation.
+//
+// This mutation represents the completion (or state transition) of an order
+// initiated earlier via InitializeCheckout / external Klarna processing.
+// It finalizes (or updates) the cart's order metadata.
+//
+// Behavior:
+//   - Validates payload non-nil and OrderId not empty.
+//   - Sets (or overwrites) OrderReference with the provided OrderId.
+//   - Sets PaymentStatus from payload.Status.
+//   - Marks PaymentInProgress = false (checkout flow finished / acknowledged).
+//   - Does NOT adjust monetary totals (no WithTotals()).
+//
+// Notes / Future Extensions:
+//   - If multiple order completion events can arrive (e.g., retries / webhook
+//     replays), this handler is idempotent: it simply overwrites fields.
+//   - If you need to guard against conflicting order IDs, add a check:
+//     if g.OrderReference != "" && g.OrderReference != m.OrderId { ... }
+//   - Add audit logging or metrics here if required.
+//
+// Concurrency:
+//   - Relies on the higher-level guarantee that Apply() calls are serialized
+//     per grain. If out-of-order events are possible, embed versioning or
+//     timestamps in the mutation and compare before applying changes.
+func init() {
+	RegisterMutation[messages.OrderCreated](
+		"OrderCreated",
+		func(g *CartGrain, m *messages.OrderCreated) error {
+			if m == nil {
+				return fmt.Errorf("OrderCreated: nil payload")
+			}
+			if m.OrderId == "" {
+				return fmt.Errorf("OrderCreated: missing orderId")
+			}
+
+			g.OrderReference = m.OrderId
+			g.PaymentStatus = m.Status
+			g.PaymentInProgress = false
+			return nil
+		},
+		// No WithTotals(): order completion does not modify pricing or taxes.
+	)
+}

mutation_registry.go

@@ -0,0 +1,301 @@
+package main
+
+import (
+	"fmt"
+	"reflect"
+	"sync"
+)
+
+// mutation_registry.go
+//
+// Mutation Registry Infrastructure
+// --------------------------------
+// This file introduces a generic registry for cart mutations that:
+//
+// 1. Decouples mutation logic from the large type-switch inside CartGrain.Apply.
+// 2. Enforces (at registration time) that every mutation handler has the correct
+//    signature: func(*CartGrain, *T) error
+// 3. Optionally auto-updates cart totals after a mutation if flagged.
+// 4. Provides a single authoritative list of registered mutations for
+//    introspection / coverage testing.
+// 5. Allows incremental migration: you can first register new mutations here,
+//    and later prune the legacy switch cases.
+//
+// Usage Pattern
+// -------------
+//   // Define your mutation proto message (e.g. messages.ApplyCoupon in messages.proto)
+//   // Regenerate protobufs.
+//
+//   // In an init() (ideally in a small file like mutations_apply_coupon.go)
+//   func init() {
+//       RegisterMutation[*messages.ApplyCoupon](
+//           "ApplyCoupon",
+//           func(g *CartGrain, m *messages.ApplyCoupon) error {
+//               // domain logic ...
+//               discount := int64(5000)
+//               if g.TotalPrice < discount {
+//                   discount = g.TotalPrice
+//               }
+//               g.TotalDiscount += discount
+//               g.TotalPrice -= discount
+//               return nil
+//           },
+//           WithTotals(), // we changed price-related fields; recalc totals
+//       )
+//   }
+//
+//   // To invoke dynamically (alternative to the current switch):
+//   if updated, err := ApplyRegistered(grain, incomingMessage); err == nil {
+//       grain = updated
+//   } else if errors.Is(err, ErrMutationNotRegistered) {
+//       // fallback to legacy switch logic
+//   }
+//
+// Migration Strategy
+// ------------------
+// 1. For each existing mutation handled in CartGrain.Apply, add a registry
+//    registration with equivalent logic.
+// 2. Add a test that enumerates all *expected* mutation proto types and asserts
+//    they are present in RegisteredMutationTypes().
+// 3. Once coverage is 100%, replace the switch in CartGrain.Apply with a call
+//    to ApplyRegistered (and optionally keep a minimal default to produce an
+//    "unsupported mutation" error).
+//
+// Thread Safety
+// -------------
+// Registration is typically done at init() time; a RWMutex provides safety
+// should late dynamic registration ever be introduced.
+//
+// Auto Totals
+// -----------
+// Many mutations require recomputing totals. To avoid forgetting this, pass
+// WithTotals() when registering. This will invoke grain.UpdateTotals() after
+// the handler returns successfully.
+//
+// Error Semantics
+// ---------------
+// - If a handler returns an error, totals are NOT recalculated (even if
+//   WithTotals() was specified).
+// - ApplyRegistered returns (nil, ErrMutationNotRegistered) if the message type
+//   is absent.
+//
+// Extensibility
+// -------------
+// It is straightforward to add options like audit hooks, metrics wrappers,
+// or optimistic concurrency guards by extending MutationOption.
+//
+// NOTE: Generics require Go 1.18+. If constrained to earlier Go versions,
+//       replace the generic registration with a non-generic RegisterMutationType
+//       that accepts reflect.Type and an adapter function.
+//
+// ---------------------------------------------------------------------------
+
+var (
+	mutationRegistryMu sync.RWMutex
+	mutationRegistry   = make(map[reflect.Type]*registeredMutation)
+
+	// ErrMutationNotRegistered is returned when no handler exists for a given mutation type.
+	ErrMutationNotRegistered = fmt.Errorf("mutation not registered")
+)
+
+// MutationOption configures additional behavior for a registered mutation.
+type MutationOption func(*mutationOptions)
+
+// mutationOptions holds flags adjustable per registration.
+type mutationOptions struct {
+	updateTotals bool
+}
+
+// WithTotals ensures CartGrain.UpdateTotals() is called after a successful handler.
+func WithTotals() MutationOption {
+	return func(o *mutationOptions) {
+		o.updateTotals = true
+	}
+}
+
+// registeredMutation stores metadata + the execution closure.
+type registeredMutation struct {
+	name         string
+	handler      func(*CartGrain, interface{}) error
+	updateTotals bool
+	msgType      reflect.Type
+}
+
+// RegisterMutation registers a mutation handler for a specific message type T.
+//
+// Parameters:
+//
+//	name    - a human-readable identifier (used for diagnostics / coverage tests).
+//	handler - business logic operating on the cart grain & strongly typed message.
+//	options - optional behavior flags (e.g., WithTotals()).
+//
+// Panics if:
+//   - name is empty
+//   - handler is nil
+//   - duplicate registration for the same message type T
+//
+// Typical call is placed in an init() function.
+func RegisterMutation[T any](name string, handler func(*CartGrain, *T) error, options ...MutationOption) {
+	if name == "" {
+		panic("RegisterMutation: name is required")
+	}
+	if handler == nil {
+		panic("RegisterMutation: handler is nil")
+	}
+
+	// Derive the reflect.Type for *T then its Elem (T) for mapping.
+	var zero *T
+	rtPtr := reflect.TypeOf(zero)
+	if rtPtr.Kind() != reflect.Ptr {
+		panic("RegisterMutation: expected pointer type for generic parameter")
+	}
+	rt := rtPtr.Elem()
+
+	opts := mutationOptions{}
+	for _, opt := range options {
+		opt(&opts)
+	}
+
+	wrapped := func(g *CartGrain, m interface{}) error {
+		typed, ok := m.(*T)
+		if !ok {
+			return fmt.Errorf("mutation type mismatch: have %T want *%s", m, rt.Name())
+		}
+		return handler(g, typed)
+	}
+
+	mutationRegistryMu.Lock()
+	defer mutationRegistryMu.Unlock()
+
+	if _, exists := mutationRegistry[rt]; exists {
+		panic(fmt.Sprintf("RegisterMutation: duplicate registration for type %s", rt.String()))
+	}
+
+	mutationRegistry[rt] = &registeredMutation{
+		name:         name,
+		handler:      wrapped,
+		updateTotals: opts.updateTotals,
+		msgType:      rt,
+	}
+}
+
+// ApplyRegistered attempts to apply a registered mutation.
+// Returns updated grain if successful.
+//
+// If the mutation is not registered, returns (nil, ErrMutationNotRegistered).
+func ApplyRegistered(grain *CartGrain, msg interface{}) (*CartGrain, error) {
+	if grain == nil {
+		return nil, fmt.Errorf("nil grain")
+	}
+	if msg == nil {
+		return nil, fmt.Errorf("nil mutation message")
+	}
+
+	rt := indirectType(reflect.TypeOf(msg))
+	mutationRegistryMu.RLock()
+	entry, ok := mutationRegistry[rt]
+	mutationRegistryMu.RUnlock()
+
+	if !ok {
+		return nil, ErrMutationNotRegistered
+	}
+
+	if err := entry.handler(grain, msg); err != nil {
+		return nil, err
+	}
+
+	if entry.updateTotals {
+		grain.UpdateTotals()
+	}
+
+	return grain, nil
+}
+
+// RegisteredMutations returns metadata for all registered mutations (snapshot).
+func RegisteredMutations() []string {
+	mutationRegistryMu.RLock()
+	defer mutationRegistryMu.RUnlock()
+	out := make([]string, 0, len(mutationRegistry))
+	for _, entry := range mutationRegistry {
+		out = append(out, entry.name)
+	}
+	return out
+}
+
+// RegisteredMutationTypes returns the reflect.Type list of all registered messages.
+// Useful for coverage tests ensuring expected set matches actual set.
+func RegisteredMutationTypes() []reflect.Type {
+	mutationRegistryMu.RLock()
+	defer mutationRegistryMu.RUnlock()
+	out := make([]reflect.Type, 0, len(mutationRegistry))
+	for t := range mutationRegistry {
+		out = append(out, t)
+	}
+	return out
+}
+
+// MustAssertMutationCoverage can be called at startup to ensure every expected
+// mutation type has been registered. It panics with a descriptive message if any
+// are missing. Provide a slice of prototype pointers (e.g. []*messages.AddItem{nil} ...)
+func MustAssertMutationCoverage(expected []interface{}) {
+	mutationRegistryMu.RLock()
+	defer mutationRegistryMu.RUnlock()
+
+	missing := make([]string, 0)
+	for _, ex := range expected {
+		if ex == nil {
+			continue
+		}
+		t := indirectType(reflect.TypeOf(ex))
+		if _, ok := mutationRegistry[t]; !ok {
+			missing = append(missing, t.String())
+		}
+	}
+	if len(missing) > 0 {
+		panic(fmt.Sprintf("mutation registry missing handlers for: %v", missing))
+	}
+}
+
+// indirectType returns the element type if given a pointer; otherwise the type itself.
+func indirectType(t reflect.Type) reflect.Type {
+	for t.Kind() == reflect.Ptr {
+		t = t.Elem()
+	}
+	return t
+}
+
+/*
+Integration Guide
+-----------------
+
+1. Register all existing mutations:
+
+   func init() {
+       RegisterMutation[*messages.AddItem]("AddItem",
+           func(g *CartGrain, m *messages.AddItem) error {
+               // (port logic from existing switch branch)
+               // ...
+               return nil
+           },
+           WithTotals(),
+       )
+       // ... repeat for others
+   }
+
+2. In CartGrain.Apply (early in the method) add:
+
+   if updated, err := ApplyRegistered(c, content); err == nil {
+       return updated, nil
+   } else if err != ErrMutationNotRegistered {
+       return nil, err
+   }
+
+   // existing switch fallback below
+
+3. Once all mutations are registered, remove the legacy switch cases
+   and leave a single ErrMutationNotRegistered path for unknown types.
+
+4. Add a coverage test (see docs for example; removed from source for clarity).
+5. (Optional) Add metrics / tracing wrappers for handlers.
+
+*/

mutation_remove_delivery.go

@@ -0,0 +1,53 @@
+package main
+
+import (
+	"fmt"
+
+	messages "git.tornberg.me/go-cart-actor/proto"
+)
+
+// mutation_remove_delivery.go
+//
+// Registers the RemoveDelivery mutation.
+//
+// Behavior:
+//   - Removes the delivery entry whose Id == payload.Id.
+//   - If not found, returns an error.
+//   - Cart totals are recalculated (WithTotals) after removal.
+//   - Items previously associated with that delivery simply become "without delivery";
+//     subsequent delivery mutations can reassign them.
+//
+// Differences vs legacy:
+//   - Legacy logic decremented TotalPrice explicitly before recalculating.
+//     Here we rely solely on UpdateTotals() to recompute from remaining
+//     deliveries and items (simpler / single source of truth).
+//
+// Future considerations:
+//   - If delivery pricing logic changes (e.g., dynamic taxes per delivery),
+//     UpdateTotals() may need enhancement to incorporate delivery tax properly.
+func init() {
+	RegisterMutation[messages.RemoveDelivery](
+		"RemoveDelivery",
+		func(g *CartGrain, m *messages.RemoveDelivery) error {
+			if m == nil {
+				return fmt.Errorf("RemoveDelivery: nil payload")
+			}
+			targetID := int(m.Id)
+			index := -1
+			for i, d := range g.Deliveries {
+				if d.Id == targetID {
+					index = i
+					break
+				}
+			}
+			if index == -1 {
+				return fmt.Errorf("RemoveDelivery: delivery id %d not found", m.Id)
+			}
+
+			// Remove delivery (order not preserved beyond necessity)
+			g.Deliveries = append(g.Deliveries[:index], g.Deliveries[index+1:]...)
+			return nil
+		},
+		WithTotals(),
+	)
+}

mutation_remove_item.go

@@ -0,0 +1,49 @@
+package main
+
+import (
+	"fmt"
+
+	messages "git.tornberg.me/go-cart-actor/proto"
+)
+
+// mutation_remove_item.go
+//
+// Registers the RemoveItem mutation.
+//
+// Behavior:
+//   - Removes the cart line whose local cart line Id == payload.Id
+//   - If no such line exists returns an error
+//   - Recalculates cart totals (WithTotals)
+//
+// Notes:
+//   - This removes only the line item; any deliveries referencing the removed
+//     item are NOT automatically adjusted (mirrors prior logic). If future
+//     semantics require pruning delivery.item_ids you can extend this handler.
+//   - If multiple lines somehow shared the same Id (should not happen), only
+//     the first match would be removed—data integrity relies on unique line Ids.
+func init() {
+	RegisterMutation[messages.RemoveItem](
+		"RemoveItem",
+		func(g *CartGrain, m *messages.RemoveItem) error {
+			if m == nil {
+				return fmt.Errorf("RemoveItem: nil payload")
+			}
+			targetID := int(m.Id)
+
+			index := -1
+			for i, it := range g.Items {
+				if it.Id == targetID {
+					index = i
+					break
+				}
+			}
+			if index == -1 {
+				return fmt.Errorf("RemoveItem: item id %d not found", m.Id)
+			}
+
+			g.Items = append(g.Items[:index], g.Items[index+1:]...)
+			return nil
+		},
+		WithTotals(),
+	)
+}

mutation_set_cart_items.go

@@ -0,0 +1,57 @@
+package main
+
+import (
+	"fmt"
+
+	messages "git.tornberg.me/go-cart-actor/proto"
+)
+
+// mutation_set_cart_items.go
+//
+// Registers the SetCartRequest mutation. This mutation replaces the entire list
+// of cart items with the provided list (each entry is an AddRequest).
+//
+// Behavior:
+//   - Clears existing items (but leaves deliveries intact).
+//   - Iterates over each AddRequest and delegates to CartGrain.AddItem
+//     (which performs product lookup, creates AddItem mutation).
+//   - If any single addition fails, the mutation aborts with an error;
+//     items added prior to the failure remain (consistent with previous behavior).
+//   - Totals recalculated after completion via WithTotals().
+//
+// Notes:
+//   - Potential optimization: batch product lookups; currently sequential.
+//   - Consider adding rollback semantics if atomic replacement is desired.
+//   - Deliveries might reference item IDs that are now invalid—original logic
+//     also left deliveries untouched. If that becomes an issue, add a cleanup
+//     pass to remove deliveries whose item IDs no longer exist.
+func init() {
+	RegisterMutation[messages.SetCartRequest](
+		"SetCartRequest",
+		func(g *CartGrain, m *messages.SetCartRequest) error {
+			if m == nil {
+				return fmt.Errorf("SetCartRequest: nil payload")
+			}
+
+			// Clear current items (keep deliveries)
+			g.mu.Lock()
+			g.Items = make([]*CartItem, 0, len(m.Items))
+			g.mu.Unlock()
+
+			for _, it := range m.Items {
+				if it == nil {
+					continue
+				}
+				if it.Sku == "" || it.Quantity < 1 {
+					return fmt.Errorf("SetCartRequest: invalid item (sku='%s' qty=%d)", it.Sku, it.Quantity)
+				}
+				_, err := g.AddItem(it.Sku, int(it.Quantity), it.Country, it.StoreId)
+				if err != nil {
+					return fmt.Errorf("SetCartRequest: add sku '%s' failed: %w", it.Sku, err)
+				}
+			}
+			return nil
+		},
+		WithTotals(),
+	)
+}

mutation_set_delivery.go

@@ -0,0 +1,101 @@
+package main
+
+import (
+	"fmt"
+	"slices"
+
+	messages "git.tornberg.me/go-cart-actor/proto"
+)
+
+// mutation_set_delivery.go
+//
+// Registers the SetDelivery mutation.
+//
+// Semantics (mirrors legacy switch logic):
+//   - If the payload specifies an explicit list of item IDs (payload.Items):
+//   - Each referenced cart line must exist.
+//   - None of the referenced items may already belong to a delivery.
+//   - Only those items are associated with the new delivery.
+//   - If payload.Items is empty:
+//   - All items currently without any delivery are associated with the new delivery.
+//   - A new delivery line is created with:
+//   - Auto-incremented delivery ID (cart-local)
+//   - Provider from payload
+//   - Fixed price (currently hard-coded: 4900 minor units) – adjust as needed
+//   - Optional PickupPoint copied from payload
+//   - Cart totals are recalculated (WithTotals)
+//
+// Error cases:
+//   - Referenced item does not exist
+//   - Referenced item already has a delivery
+//   - No items qualify (resulting association set empty) -> returns error (prevents creating empty delivery)
+//
+// Concurrency:
+//   - Uses g.mu to protect lastDeliveryId increment and append to Deliveries slice.
+//     Item scans are read-only and performed outside the lock for simplicity;
+//     if stricter guarantees are needed, widen the lock section.
+//
+// Future extension points:
+//   - Variable delivery pricing (based on weight, distance, provider, etc.)
+//   - Validation of provider codes
+//   - Multi-currency delivery pricing
+func init() {
+	RegisterMutation[messages.SetDelivery](
+		"SetDelivery",
+		func(g *CartGrain, m *messages.SetDelivery) error {
+			if m == nil {
+				return fmt.Errorf("SetDelivery: nil payload")
+			}
+			if m.Provider == "" {
+				return fmt.Errorf("SetDelivery: provider is empty")
+			}
+
+			withDelivery := g.ItemsWithDelivery()
+			targetItems := make([]int, 0)
+
+			if len(m.Items) == 0 {
+				// Use every item currently without a delivery
+				targetItems = append(targetItems, g.ItemsWithoutDelivery()...)
+			} else {
+				// Validate explicit list
+				for _, id64 := range m.Items {
+					id := int(id64)
+					found := false
+					for _, it := range g.Items {
+						if it.Id == id {
+							found = true
+							break
+						}
+					}
+					if !found {
+						return fmt.Errorf("SetDelivery: item id %d not found", id)
+					}
+					if slices.Contains(withDelivery, id) {
+						return fmt.Errorf("SetDelivery: item id %d already has a delivery", id)
+					}
+					targetItems = append(targetItems, id)
+				}
+			}
+
+			if len(targetItems) == 0 {
+				return fmt.Errorf("SetDelivery: no eligible items to attach")
+			}
+
+			// Append new delivery
+			g.mu.Lock()
+			g.lastDeliveryId++
+			newId := g.lastDeliveryId
+			g.Deliveries = append(g.Deliveries, &CartDelivery{
+				Id:          newId,
+				Provider:    m.Provider,
+				PickupPoint: m.PickupPoint,
+				Price:       4900, // TODO: externalize pricing
+				Items:       targetItems,
+			})
+			g.mu.Unlock()
+
+			return nil
+		},
+		WithTotals(),
+	)
+}

mutation_set_pickup_point.go

@@ -0,0 +1,56 @@
+package main
+
+import (
+	"fmt"
+
+	messages "git.tornberg.me/go-cart-actor/proto"
+)
+
+// mutation_set_pickup_point.go
+//
+// Registers the SetPickupPoint mutation using the generic mutation registry.
+//
+// Semantics (mirrors original switch-based implementation):
+//   - Locate the delivery with Id == payload.DeliveryId
+//   - Set (or overwrite) its PickupPoint with the provided data
+//   - Does NOT alter pricing or taxes (so no totals recalculation required)
+//
+// Validation / Error Handling:
+//   - If payload is nil -> error
+//   - If DeliveryId not found -> error
+//
+// Concurrency:
+//   - Relies on the existing expectation that higher-level mutation routing
+//     serializes Apply() calls per grain; if stricter guarantees are needed,
+//     a delivery-level lock could be introduced later.
+//
+// Future Extensions:
+//   - Validate pickup point fields (country code, zip format, etc.)
+//   - Track history / audit of pickup point changes
+//   - Trigger delivery price adjustments (which would then require WithTotals()).
+func init() {
+	RegisterMutation[messages.SetPickupPoint](
+		"SetPickupPoint",
+		func(g *CartGrain, m *messages.SetPickupPoint) error {
+			if m == nil {
+				return fmt.Errorf("SetPickupPoint: nil payload")
+			}
+
+			for _, d := range g.Deliveries {
+				if d.Id == int(m.DeliveryId) {
+					d.PickupPoint = &messages.PickupPoint{
+						Id:      m.Id,
+						Name:    m.Name,
+						Address: m.Address,
+						City:    m.City,
+						Zip:     m.Zip,
+						Country: m.Country,
+					}
+					return nil
+				}
+			}
+			return fmt.Errorf("SetPickupPoint: delivery id %d not found", m.DeliveryId)
+		},
+		// No WithTotals(): pickup point does not change pricing / tax.
+	)
+}

pool-server.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"bytes"
 	"encoding/json"
 	"fmt"
 	"log"
@@ -24,21 +25,26 @@ func NewPoolServer(pool GrainPool, pod_name string) *PoolServer {
 	}
 }
 
+func (s *PoolServer) process(id CartId, mutation interface{}) (*messages.CartState, error) {
+	grain, err := s.pool.Apply(id, mutation)
+	if err != nil {
+		return nil, err
+	}
+	return ToCartState(grain), nil
+}
+
 func (s *PoolServer) HandleGet(w http.ResponseWriter, r *http.Request, id CartId) error {
-	data, err := s.pool.Get(id)
+	grain, err := s.pool.Get(id)
 	if err != nil {
 		return err
 	}
 
-	return s.WriteResult(w, data)
+	return s.WriteResult(w, ToCartState(grain))
 }
 
 func (s *PoolServer) HandleAddSku(w http.ResponseWriter, r *http.Request, id CartId) error {
 	sku := r.PathValue("sku")
-	data, err := s.pool.Process(id, Message{
+	data, err := s.process(id, &messages.AddRequest{Sku: sku, Quantity: 1})
-		Type:    AddRequestType,
-		Content: &messages.AddRequest{Sku: sku, Quantity: 1},
-	})
 	if err != nil {
 		return err
 	}
@@ -56,23 +62,20 @@ func ErrorHandler(fn func(w http.ResponseWriter, r *http.Request) error) func(w
 	}
 }
 
-func (s *PoolServer) WriteResult(w http.ResponseWriter, result *FrameWithPayload) error {
+func (s *PoolServer) WriteResult(w http.ResponseWriter, result *messages.CartState) error {
 	w.Header().Set("Content-Type", "application/json")
 	w.Header().Set("Cache-Control", "no-cache")
 	w.Header().Set("Access-Control-Allow-Origin", "*")
 	w.Header().Set("X-Pod-Name", s.pod_name)
-	if result.StatusCode != 200 {
+	if result == nil {
-		log.Printf("Call error: %d\n", result.StatusCode)
+
-		if result.StatusCode >= 200 && result.StatusCode < 600 {
+		w.WriteHeader(http.StatusInternalServerError)
-			w.WriteHeader(int(result.StatusCode))
+
-		} else {
-			w.WriteHeader(http.StatusInternalServerError)
-		}
-		w.Write([]byte(result.Payload))
 		return nil
 	}
 	w.WriteHeader(http.StatusOK)
-	_, err := w.Write(result.Payload)
+	enc := json.NewEncoder(w)
+	err := enc.Encode(result)
 	return err
 }
 
@@ -83,10 +86,7 @@ func (s *PoolServer) HandleDeleteItem(w http.ResponseWriter, r *http.Request, id
 	if err != nil {
 		return err
 	}
-	data, err := s.pool.Process(id, Message{
+	data, err := s.process(id, &messages.RemoveItem{Id: int64(itemId)})
-		Type:    RemoveItemType,
-		Content: &messages.RemoveItem{Id: int64(itemId)},
-	})
 	if err != nil {
 		return err
 	}
@@ -106,13 +106,10 @@ func (s *PoolServer) HandleSetDelivery(w http.ResponseWriter, r *http.Request, i
 	if err != nil {
 		return err
 	}
-	data, err := s.pool.Process(id, Message{
+	data, err := s.process(id, &messages.SetDelivery{
-		Type: SetDeliveryType,
+		Provider:    delivery.Provider,
-		Content: &messages.SetDelivery{
+		Items:       delivery.Items,
-			Provider:    delivery.Provider,
+		PickupPoint: delivery.PickupPoint,
-			Items:       delivery.Items,
-			PickupPoint: delivery.PickupPoint,
-		},
 	})
 	if err != nil {
 		return err
@@ -132,17 +129,14 @@ func (s *PoolServer) HandleSetPickupPoint(w http.ResponseWriter, r *http.Request
 	if err != nil {
 		return err
 	}
-	reply, err := s.pool.Process(id, Message{
+	reply, err := s.process(id, &messages.SetPickupPoint{
-		Type: SetPickupPointType,
+		DeliveryId: int64(deliveryId),
-		Content: &messages.SetPickupPoint{
+		Id:         pickupPoint.Id,
-			DeliveryId: int64(deliveryId),
+		Name:       pickupPoint.Name,
-			Id:         pickupPoint.Id,
+		Address:    pickupPoint.Address,
-			Name:       pickupPoint.Name,
+		City:       pickupPoint.City,
-			Address:    pickupPoint.Address,
+		Zip:        pickupPoint.Zip,
-			City:       pickupPoint.City,
+		Country:    pickupPoint.Country,
-			Zip:        pickupPoint.Zip,
-			Country:    pickupPoint.Country,
-		},
 	})
 	if err != nil {
 		return err
@@ -157,10 +151,7 @@ func (s *PoolServer) HandleRemoveDelivery(w http.ResponseWriter, r *http.Request
 	if err != nil {
 		return err
 	}
-	reply, err := s.pool.Process(id, Message{
+	reply, err := s.process(id, &messages.RemoveDelivery{Id: int64(deliveryId)})
-		Type:    RemoveDeliveryType,
-		Content: &messages.RemoveDelivery{Id: int64(deliveryId)},
-	})
 	if err != nil {
 		return err
 	}
@@ -173,10 +164,7 @@ func (s *PoolServer) HandleQuantityChange(w http.ResponseWriter, r *http.Request
 	if err != nil {
 		return err
 	}
-	reply, err := s.pool.Process(id, Message{
+	reply, err := s.process(id, &changeQuantity)
-		Type:    ChangeQuantityType,
-		Content: &changeQuantity,
-	})
 	if err != nil {
 		return err
 	}
@@ -189,10 +177,7 @@ func (s *PoolServer) HandleSetCartItems(w http.ResponseWriter, r *http.Request,
 	if err != nil {
 		return err
 	}
-	reply, err := s.pool.Process(id, Message{
+	reply, err := s.process(id, &setCartItems)
-		Type:    SetCartItemsType,
-		Content: &setCartItems,
-	})
 	if err != nil {
 		return err
 	}
@@ -205,10 +190,7 @@ func (s *PoolServer) HandleAddRequest(w http.ResponseWriter, r *http.Request, id
 	if err != nil {
 		return err
 	}
-	reply, err := s.pool.Process(id, Message{
+	reply, err := s.process(id, &addRequest)
-		Type:    AddRequestType,
-		Content: &addRequest,
-	})
 	if err != nil {
 		return err
 	}
@@ -234,58 +216,115 @@ func (s *PoolServer) HandleConfirmation(w http.ResponseWriter, r *http.Request,
 	return json.NewEncoder(w).Encode(order)
 }
 
-func (s *PoolServer) HandleCheckout(w http.ResponseWriter, r *http.Request, id CartId) error {
+func (s *PoolServer) CreateOrUpdateCheckout(host string, id CartId) (*CheckoutOrder, error) {
+	meta := &CheckoutMeta{
+		Terms:        fmt.Sprintf("https://%s/terms", host),
+		Checkout:     fmt.Sprintf("https://%s/checkout?order_id={checkout.order.id}", host),
+		Confirmation: fmt.Sprintf("https://%s/confirmation/{checkout.order.id}", host),
+		Validation:   fmt.Sprintf("https://%s/validate", host),
+		Push:         fmt.Sprintf("https://%s/push?order_id={checkout.order.id}", host),
+		Country:      getCountryFromHost(host),
+	}
 
-	reply, err := s.pool.Process(id, Message{
+	// Get current grain state (may be local or remote)
-		Type: CreateCheckoutOrderType,
+	grain, err := s.pool.Get(id)
-		Content: &messages.CreateCheckoutOrder{
+	if err != nil {
-			Terms:        "https://slask-finder.tornberg.me/terms",
+		return nil, err
-			Checkout:     "https://slask-finder.tornberg.me/checkout?order_id={checkout.order.id}",
+	}
-			Confirmation: "https://slask-finder.tornberg.me/confirmation/{checkout.order.id}",
+
-			Push:         "https://cart.tornberg.me/push?order_id={checkout.order.id}",
+	// Build pure checkout payload
-		},
+	payload, _, err := BuildCheckoutOrderPayload(grain, meta)
+	if err != nil {
+		return nil, err
+	}
+
+	if grain.OrderReference != "" {
+		return KlarnaInstance.UpdateOrder(grain.OrderReference, bytes.NewReader(payload))
+	} else {
+		return KlarnaInstance.CreateOrder(bytes.NewReader(payload))
+	}
+}
+
+func (s *PoolServer) ApplyCheckoutStarted(klarnaOrder *CheckoutOrder, id CartId) (*CartGrain, error) {
+	// Persist initialization state via mutation (best-effort)
+	return s.pool.Apply(id, &messages.InitializeCheckout{
+		OrderId:           klarnaOrder.ID,
+		Status:            klarnaOrder.Status,
+		PaymentInProgress: true,
 	})
+}
+
+func (s *PoolServer) HandleCheckout(w http.ResponseWriter, r *http.Request, id CartId) error {
+	klarnaOrder, err := s.CreateOrUpdateCheckout(r.Host, id)
 	if err != nil {
 		return err
 	}
-	if reply.StatusCode != 200 {
-		return s.WriteResult(w, reply)
-	}
 
-	// w.Header().Set("Content-Type", "application/json")
+	s.ApplyCheckoutStarted(klarnaOrder, id)
-	// w.Header().Set("X-Pod-Name", s.pod_name)
-	// w.Header().Set("Cache-Control", "no-cache")
-	// w.Header().Set("Access-Control-Allow-Origin", "*")
-	// w.WriteHeader(http.StatusOK)
 
-	return s.WriteResult(w, reply)
+	w.Header().Set("Content-Type", "application/json")
+	return json.NewEncoder(w).Encode(klarnaOrder)
 }
 
 func NewCartId() CartId {
-	id := time.Now().UnixNano() + rand.Int63()
+	// Deprecated: legacy random/time based cart id generator.
-
+	// Retained for compatibility; new code should prefer canonical CartID path.
-	return ToCartId(fmt.Sprintf("%d", id))
+	cid, err := NewCartID()
+	if err != nil {
+		// Fallback to legacy method only if crypto/rand fails
+		id := time.Now().UnixNano() + rand.Int63()
+		return ToCartId(fmt.Sprintf("%d", id))
+	}
+	return CartIDToLegacy(cid)
 }
 
 func CookieCartIdHandler(fn func(w http.ResponseWriter, r *http.Request, cartId CartId) error) func(w http.ResponseWriter, r *http.Request) error {
 	return func(w http.ResponseWriter, r *http.Request) error {
-		var cartId CartId
+		// Extract / normalize cookie (preserve legacy textual IDs without rewriting).
-		cartIdCookie := r.CookiesNamed("cartid")
+		var legacy CartId
-		if cartIdCookie == nil || len(cartIdCookie) == 0 {
+		cookies := r.CookiesNamed("cartid")
-			cartId = NewCartId()
+		if len(cookies) == 0 {
-			http.SetCookie(w, &http.Cookie{
+			// No cookie -> generate new canonical base62 id.
-				Name:     "cartid",
+			cid, generated, _, err := CanonicalizeOrLegacy("")
-				Value:    cartId.String(),
+			if err != nil {
-				Secure:   true,
+				return fmt.Errorf("failed to generate cart id: %w", err)
-				HttpOnly: true,
+			}
-				Path:     "/",
+			legacy = CartIDToLegacy(cid)
-				Expires:  time.Now().AddDate(0, 0, 14),
+			if generated {
-				SameSite: http.SameSiteLaxMode,
+				http.SetCookie(w, &http.Cookie{
-			})
+					Name:     "cartid",
+					Value:    cid.String(),
+					Secure:   r.TLS != nil,
+					HttpOnly: true,
+					Path:     "/",
+					Expires:  time.Now().AddDate(0, 0, 14),
+					SameSite: http.SameSiteLaxMode,
+				})
+				w.Header().Set("Set-Cart-Id", cid.String())
+			}
 		} else {
-			cartId = ToCartId(cartIdCookie[0].Value)
+			raw := cookies[0].Value
+			cid, generated, wasBase62, err := CanonicalizeOrLegacy(raw)
+			if err != nil {
+				return fmt.Errorf("failed to canonicalize cart id: %w", err)
+			}
+			legacy = CartIDToLegacy(cid)
+			// Only set a new cookie if we actually generated a brand-new ID (empty input).
+			// For legacy (non-base62) ids we preserve the original text and do not overwrite.
+			if generated && wasBase62 {
+				http.SetCookie(w, &http.Cookie{
+					Name:     "cartid",
+					Value:    cid.String(),
+					Secure:   r.TLS != nil,
+					HttpOnly: true,
+					Path:     "/",
+					Expires:  time.Now().AddDate(0, 0, 14),
+					SameSite: http.SameSiteLaxMode,
+				})
+				w.Header().Set("Set-Cart-Id", cid.String())
+			}
 		}
-		return fn(w, r, cartId)
+		return fn(w, r, legacy)
 	}
 }
 
@@ -295,7 +334,7 @@ func (s *PoolServer) RemoveCartCookie(w http.ResponseWriter, r *http.Request, ca
 		Name:     "cartid",
 		Value:    cartId.String(),
 		Path:     "/",
-		Secure:   true,
+		Secure:   r.TLS != nil,
 		HttpOnly: true,
 		Expires:  time.Unix(0, 0),
 		SameSite: http.SameSiteLaxMode,
@@ -306,8 +345,18 @@ func (s *PoolServer) RemoveCartCookie(w http.ResponseWriter, r *http.Request, ca
 
 func CartIdHandler(fn func(w http.ResponseWriter, r *http.Request, cartId CartId) error) func(w http.ResponseWriter, r *http.Request) error {
 	return func(w http.ResponseWriter, r *http.Request) error {
-		cartId := ToCartId(r.PathValue("id"))
+		raw := r.PathValue("id")
-		return fn(w, r, cartId)
+		cid, generated, wasBase62, err := CanonicalizeOrLegacy(raw)
+		if err != nil {
+			return fmt.Errorf("invalid cart id: %w", err)
+		}
+		legacy := CartIDToLegacy(cid)
+		// Only emit Set-Cart-Id header if we produced a brand-new canonical id
+		// AND it is base62 (avoid rewriting legacy textual identifiers).
+		if generated && wasBase62 {
+			w.Header().Set("Set-Cart-Id", cid.String())
+		}
+		return fn(w, r, legacy)
 	}
 }
 

proto/cart_actor.proto

@@ -2,88 +2,186 @@ syntax = "proto3";
 
 package messages;
 
-option go_package = ".;messages";
+option go_package = "git.tornberg.me/go-cart-actor/proto;messages";
+
+import "messages.proto";
 
 // -----------------------------------------------------------------------------
-// Cart Actor gRPC API (Envelope Variant)
+// Cart Actor gRPC API (Breaking v2 - Per-Mutation RPCs)
 // -----------------------------------------------------------------------------
-// This service replaces the legacy custom TCP frame protocol used on port 1337.
+// This version removes the previous MutationEnvelope + Mutate RPC.
-// It keeps the existing per-mutation proto messages (defined in messages.proto)
+// Each mutation now has its own request wrapper and dedicated RPC method
-// serialized into an opaque `bytes payload` field for minimal refactor cost.
+// providing simpler, type-focused client stubs and enabling per-mutation
-// The numeric values in MutationType MUST match the legacy message type
+// metrics, auth and rate limiting.
-// constants (see message-types.go) so persisted event logs replay correctly.
+//
+// Regenerate Go code after editing:
+//   protoc --go_out=. --go_opt=paths=source_relative \
+//          --go-grpc_out=. --go-grpc_opt=paths=source_relative \
+//          proto/cart_actor.proto proto/messages.proto
+//
+// Backward compatibility: This is a breaking change (old clients must update).
 // -----------------------------------------------------------------------------
 
-// MutationType corresponds 1:1 with the legacy uint16 message type constants.
+// Shared reply for all mutation RPCs.
-enum MutationType {
+message CartMutationReply {
-  MUTATION_TYPE_UNSPECIFIED        = 0;
+  int32 status_code = 1;          // HTTP-like status (200 success, 4xx client, 5xx server)
-  MUTATION_ADD_REQUEST             = 1;
+  oneof result {
-  MUTATION_ADD_ITEM                = 2;
+    CartState state = 2;          // Updated cart state on success
-  // (3 was unused / reserved in legacy framing)
+    string error = 3;             // Error message on failure
-  MUTATION_REMOVE_ITEM             = 4;
+  }
-  MUTATION_REMOVE_DELIVERY         = 5;
+  int64 server_timestamp = 4;     // Server-assigned Unix timestamp (optional auditing)
-  MUTATION_CHANGE_QUANTITY         = 6;
-  MUTATION_SET_DELIVERY            = 7;
-  MUTATION_SET_PICKUP_POINT        = 8;
-  MUTATION_CREATE_CHECKOUT_ORDER   = 9;
-  MUTATION_SET_CART_ITEMS          = 10;
-  MUTATION_ORDER_COMPLETED         = 11;
 }
 
-// MutationRequest is an envelope:
+// Fetch current cart state without mutation.
-// - cart_id: string form of CartId (legacy 16-byte array truncated/padded).
-// - type: mutation kind (see enum).
-// - payload: serialized underlying proto message (AddRequest, AddItem, etc.).
-// - client_timestamp: optional unix timestamp; server sets if zero.
-message MutationRequest {
-  string cart_id        = 1;
-  MutationType type     = 2;
-  bytes payload         = 3;
-  int64 client_timestamp = 4;
-}
-
-// MutationReply returns a status code (legacy semantics) plus a JSON payload
-// representing the full cart state (or an error message if non-200).
-message MutationReply {
-  int32 status_code = 1;
-  bytes payload     = 2; // JSON cart state or error string
-}
-
-// StateRequest fetches current cart state without mutation.
 message StateRequest {
   string cart_id = 1;
 }
 
-// StateReply mirrors MutationReply for consistency.
 message StateReply {
   int32 status_code = 1;
-  bytes payload     = 2; // JSON cart state or error string
+  oneof result {
+    CartState state = 2;
+    string error = 3;
+  }
 }
 
-// CartActor exposes mutation and state retrieval for remote grains.
+// Per-mutation request wrappers. We wrap the existing inner mutation
-service CartActor {
+// messages (defined in messages.proto) to add cart_id + optional metadata
-  // Mutate applies a single mutation to a cart, creating the cart lazily if needed.
+// without altering the inner message definitions.
-  rpc Mutate(MutationRequest) returns (MutationReply);
+
+message AddRequestRequest {
+  string cart_id = 1;
+  int64 client_timestamp = 2;
+  AddRequest payload = 10;
+}
+
+message AddItemRequest {
+  string cart_id = 1;
+  int64 client_timestamp = 2;
+  AddItem payload = 10;
+}
+
+message RemoveItemRequest {
+  string cart_id = 1;
+  int64 client_timestamp = 2;
+  RemoveItem payload = 10;
+}
+
+message RemoveDeliveryRequest {
+  string cart_id = 1;
+  int64 client_timestamp = 2;
+  RemoveDelivery payload = 10;
+}
+
+message ChangeQuantityRequest {
+  string cart_id = 1;
+  int64 client_timestamp = 2;
+  ChangeQuantity payload = 10;
+}
+
+message SetDeliveryRequest {
+  string cart_id = 1;
+  int64 client_timestamp = 2;
+  SetDelivery payload = 10;
+}
+
+message SetPickupPointRequest {
+  string cart_id = 1;
+  int64 client_timestamp = 2;
+  SetPickupPoint payload = 10;
+}
+
+message CreateCheckoutOrderRequest {
+  string cart_id = 1;
+  int64 client_timestamp = 2;
+  CreateCheckoutOrder payload = 10;
+}
+
+message SetCartItemsRequest {
+  string cart_id = 1;
+  int64 client_timestamp = 2;
+  SetCartRequest payload = 10;
+}
+
+message OrderCompletedRequest {
+  string cart_id = 1;
+  int64 client_timestamp = 2;
+  OrderCreated payload = 10;
+}
+
+// Excerpt: updated messages for camelCase JSON output
+message CartState {
+  string id = 1;                         // was cart_id
+  repeated CartItemState items = 2;
+  int64 totalPrice = 3;                  // was total_price
+  int64 totalTax = 4;                    // was total_tax
+  int64 totalDiscount = 5;               // was total_discount
+  repeated DeliveryState deliveries = 6;
+  bool paymentInProgress = 7;            // was payment_in_progress
+  string orderReference = 8;             // was order_reference
+  string paymentStatus = 9;              // was payment_status
+  bool processing = 10;                  // NEW (mirrors legacy CartGrain.processing)
+}
+
+message CartItemState {
+  int64 id = 1;
+  int64 itemId = 2;                      // was source_item_id
+  string sku = 3;
+  string name = 4;
+  int64 price = 5;                       // was unit_price
+  int32 qty = 6;                         // was quantity
+  int64 totalPrice = 7;                  // was total_price
+  int64 totalTax = 8;                    // was total_tax
+  int64 orgPrice = 9;                    // was org_price
+  int32 taxRate = 10;                    // was tax_rate
+  int64 totalDiscount = 11;
+  string brand = 12;
+  string category = 13;
+  string category2 = 14;
+  string category3 = 15;
+  string category4 = 16;
+  string category5 = 17;
+  string image = 18;
+  string type = 19;                      // was article_type
+  string sellerId = 20;                  // was seller_id
+  string sellerName = 21;                // was seller_name
+  string disclaimer = 22;
+  string outlet = 23;
+  string storeId = 24;                   // was store_id
+  int32 stock = 25;
+}
+
+message DeliveryState {
+  int64 id = 1;
+  string provider = 2;
+  int64 price = 3;
+  repeated int64 items = 4;              // was item_ids
+  PickupPoint pickupPoint = 5;           // was pickup_point
+}
+
+// (CheckoutRequest / CheckoutReply removed - checkout handled at HTTP layer)
+
+// -----------------------------------------------------------------------------
+// Service definition (per-mutation RPCs + checkout)
+// -----------------------------------------------------------------------------
+service CartActor {
+  rpc AddRequest(AddRequestRequest) returns (CartMutationReply);
+  rpc AddItem(AddItemRequest) returns (CartMutationReply);
+  rpc RemoveItem(RemoveItemRequest) returns (CartMutationReply);
+  rpc RemoveDelivery(RemoveDeliveryRequest) returns (CartMutationReply);
+  rpc ChangeQuantity(ChangeQuantityRequest) returns (CartMutationReply);
+  rpc SetDelivery(SetDeliveryRequest) returns (CartMutationReply);
+  rpc SetPickupPoint(SetPickupPointRequest) returns (CartMutationReply);
+  // (Checkout RPC removed - handled externally)
+  rpc SetCartItems(SetCartItemsRequest) returns (CartMutationReply);
+  rpc OrderCompleted(OrderCompletedRequest) returns (CartMutationReply);
 
-  // GetState retrieves the cart's current state (JSON).
   rpc GetState(StateRequest) returns (StateReply);
 }
 
 // -----------------------------------------------------------------------------
-// Notes:
+// Future enhancements:
-//
+// * BatchMutate RPC (repeated heterogeneous mutations)
-// 1. Generation:
+// * Streaming state updates (WatchState)
-//    protoc --go_out=. --go_opt=paths=source_relative \
+// * Versioning / optimistic concurrency control
-//           --go-grpc_out=. --go-grpc_opt=paths=source_relative \
-//           cart_actor.proto
-//
-// 2. Underlying mutation payloads originate from messages.proto definitions.
-//    The server side will route based on MutationType and decode payload bytes
-//    using existing handler registry logic.
-//
-// 3. Future Enhancements:
-//    - Replace JSON state payload with a strongly typed CartState proto.
-//    - Add streaming RPC (e.g. WatchState) for live updates.
-//    - Migrate control plane (negotiate/ownership) into a separate proto
-//      (control_plane.proto) as per the migration plan.
 // -----------------------------------------------------------------------------

proto/cart_actor_grpc.pb.go

@@ -19,19 +19,36 @@ import (
 const _ = grpc.SupportPackageIsVersion9
 
 const (
-	CartActor_Mutate_FullMethodName   = "/messages.CartActor/Mutate"
+	CartActor_AddRequest_FullMethodName     = "/messages.CartActor/AddRequest"
-	CartActor_GetState_FullMethodName = "/messages.CartActor/GetState"
+	CartActor_AddItem_FullMethodName        = "/messages.CartActor/AddItem"
+	CartActor_RemoveItem_FullMethodName     = "/messages.CartActor/RemoveItem"
+	CartActor_RemoveDelivery_FullMethodName = "/messages.CartActor/RemoveDelivery"
+	CartActor_ChangeQuantity_FullMethodName = "/messages.CartActor/ChangeQuantity"
+	CartActor_SetDelivery_FullMethodName    = "/messages.CartActor/SetDelivery"
+	CartActor_SetPickupPoint_FullMethodName = "/messages.CartActor/SetPickupPoint"
+	CartActor_SetCartItems_FullMethodName   = "/messages.CartActor/SetCartItems"
+	CartActor_OrderCompleted_FullMethodName = "/messages.CartActor/OrderCompleted"
+	CartActor_GetState_FullMethodName       = "/messages.CartActor/GetState"
 )
 
 // CartActorClient is the client API for CartActor service.
 //
 // For semantics around ctx use and closing/ending streaming RPCs, please refer to https://pkg.go.dev/google.golang.org/grpc/?tab=doc#ClientConn.NewStream.
 //
-// CartActor exposes mutation and state retrieval for remote grains.
+// -----------------------------------------------------------------------------
+// Service definition (per-mutation RPCs + checkout)
+// -----------------------------------------------------------------------------
 type CartActorClient interface {
-	// Mutate applies a single mutation to a cart, creating the cart lazily if needed.
+	AddRequest(ctx context.Context, in *AddRequestRequest, opts ...grpc.CallOption) (*CartMutationReply, error)
-	Mutate(ctx context.Context, in *MutationRequest, opts ...grpc.CallOption) (*MutationReply, error)
+	AddItem(ctx context.Context, in *AddItemRequest, opts ...grpc.CallOption) (*CartMutationReply, error)
-	// GetState retrieves the cart's current state (JSON).
+	RemoveItem(ctx context.Context, in *RemoveItemRequest, opts ...grpc.CallOption) (*CartMutationReply, error)
+	RemoveDelivery(ctx context.Context, in *RemoveDeliveryRequest, opts ...grpc.CallOption) (*CartMutationReply, error)
+	ChangeQuantity(ctx context.Context, in *ChangeQuantityRequest, opts ...grpc.CallOption) (*CartMutationReply, error)
+	SetDelivery(ctx context.Context, in *SetDeliveryRequest, opts ...grpc.CallOption) (*CartMutationReply, error)
+	SetPickupPoint(ctx context.Context, in *SetPickupPointRequest, opts ...grpc.CallOption) (*CartMutationReply, error)
+	// (Checkout RPC removed - handled externally)
+	SetCartItems(ctx context.Context, in *SetCartItemsRequest, opts ...grpc.CallOption) (*CartMutationReply, error)
+	OrderCompleted(ctx context.Context, in *OrderCompletedRequest, opts ...grpc.CallOption) (*CartMutationReply, error)
 	GetState(ctx context.Context, in *StateRequest, opts ...grpc.CallOption) (*StateReply, error)
 }
 
@@ -43,10 +60,90 @@ func NewCartActorClient(cc grpc.ClientConnInterface) CartActorClient {
 	return &cartActorClient{cc}
 }
 
-func (c *cartActorClient) Mutate(ctx context.Context, in *MutationRequest, opts ...grpc.CallOption) (*MutationReply, error) {
+func (c *cartActorClient) AddRequest(ctx context.Context, in *AddRequestRequest, opts ...grpc.CallOption) (*CartMutationReply, error) {
 	cOpts := append([]grpc.CallOption{grpc.StaticMethod()}, opts...)
-	out := new(MutationReply)
+	out := new(CartMutationReply)
-	err := c.cc.Invoke(ctx, CartActor_Mutate_FullMethodName, in, out, cOpts...)
+	err := c.cc.Invoke(ctx, CartActor_AddRequest_FullMethodName, in, out, cOpts...)
+	if err != nil {
+		return nil, err
+	}
+	return out, nil
+}
+
+func (c *cartActorClient) AddItem(ctx context.Context, in *AddItemRequest, opts ...grpc.CallOption) (*CartMutationReply, error) {
+	cOpts := append([]grpc.CallOption{grpc.StaticMethod()}, opts...)
+	out := new(CartMutationReply)
+	err := c.cc.Invoke(ctx, CartActor_AddItem_FullMethodName, in, out, cOpts...)
+	if err != nil {
+		return nil, err
+	}
+	return out, nil
+}
+
+func (c *cartActorClient) RemoveItem(ctx context.Context, in *RemoveItemRequest, opts ...grpc.CallOption) (*CartMutationReply, error) {
+	cOpts := append([]grpc.CallOption{grpc.StaticMethod()}, opts...)
+	out := new(CartMutationReply)
+	err := c.cc.Invoke(ctx, CartActor_RemoveItem_FullMethodName, in, out, cOpts...)
+	if err != nil {
+		return nil, err
+	}
+	return out, nil
+}
+
+func (c *cartActorClient) RemoveDelivery(ctx context.Context, in *RemoveDeliveryRequest, opts ...grpc.CallOption) (*CartMutationReply, error) {
+	cOpts := append([]grpc.CallOption{grpc.StaticMethod()}, opts...)
+	out := new(CartMutationReply)
+	err := c.cc.Invoke(ctx, CartActor_RemoveDelivery_FullMethodName, in, out, cOpts...)
+	if err != nil {
+		return nil, err
+	}
+	return out, nil
+}
+
+func (c *cartActorClient) ChangeQuantity(ctx context.Context, in *ChangeQuantityRequest, opts ...grpc.CallOption) (*CartMutationReply, error) {
+	cOpts := append([]grpc.CallOption{grpc.StaticMethod()}, opts...)
+	out := new(CartMutationReply)
+	err := c.cc.Invoke(ctx, CartActor_ChangeQuantity_FullMethodName, in, out, cOpts...)
+	if err != nil {
+		return nil, err
+	}
+	return out, nil
+}
+
+func (c *cartActorClient) SetDelivery(ctx context.Context, in *SetDeliveryRequest, opts ...grpc.CallOption) (*CartMutationReply, error) {
+	cOpts := append([]grpc.CallOption{grpc.StaticMethod()}, opts...)
+	out := new(CartMutationReply)
+	err := c.cc.Invoke(ctx, CartActor_SetDelivery_FullMethodName, in, out, cOpts...)
+	if err != nil {
+		return nil, err
+	}
+	return out, nil
+}
+
+func (c *cartActorClient) SetPickupPoint(ctx context.Context, in *SetPickupPointRequest, opts ...grpc.CallOption) (*CartMutationReply, error) {
+	cOpts := append([]grpc.CallOption{grpc.StaticMethod()}, opts...)
+	out := new(CartMutationReply)
+	err := c.cc.Invoke(ctx, CartActor_SetPickupPoint_FullMethodName, in, out, cOpts...)
+	if err != nil {
+		return nil, err
+	}
+	return out, nil
+}
+
+func (c *cartActorClient) SetCartItems(ctx context.Context, in *SetCartItemsRequest, opts ...grpc.CallOption) (*CartMutationReply, error) {
+	cOpts := append([]grpc.CallOption{grpc.StaticMethod()}, opts...)
+	out := new(CartMutationReply)
+	err := c.cc.Invoke(ctx, CartActor_SetCartItems_FullMethodName, in, out, cOpts...)
+	if err != nil {
+		return nil, err
+	}
+	return out, nil
+}
+
+func (c *cartActorClient) OrderCompleted(ctx context.Context, in *OrderCompletedRequest, opts ...grpc.CallOption) (*CartMutationReply, error) {
+	cOpts := append([]grpc.CallOption{grpc.StaticMethod()}, opts...)
+	out := new(CartMutationReply)
+	err := c.cc.Invoke(ctx, CartActor_OrderCompleted_FullMethodName, in, out, cOpts...)
 	if err != nil {
 		return nil, err
 	}
@@ -67,11 +164,20 @@ func (c *cartActorClient) GetState(ctx context.Context, in *StateRequest, opts .
 // All implementations must embed UnimplementedCartActorServer
 // for forward compatibility.
 //
-// CartActor exposes mutation and state retrieval for remote grains.
+// -----------------------------------------------------------------------------
+// Service definition (per-mutation RPCs + checkout)
+// -----------------------------------------------------------------------------
 type CartActorServer interface {
-	// Mutate applies a single mutation to a cart, creating the cart lazily if needed.
+	AddRequest(context.Context, *AddRequestRequest) (*CartMutationReply, error)
-	Mutate(context.Context, *MutationRequest) (*MutationReply, error)
+	AddItem(context.Context, *AddItemRequest) (*CartMutationReply, error)
-	// GetState retrieves the cart's current state (JSON).
+	RemoveItem(context.Context, *RemoveItemRequest) (*CartMutationReply, error)
+	RemoveDelivery(context.Context, *RemoveDeliveryRequest) (*CartMutationReply, error)
+	ChangeQuantity(context.Context, *ChangeQuantityRequest) (*CartMutationReply, error)
+	SetDelivery(context.Context, *SetDeliveryRequest) (*CartMutationReply, error)
+	SetPickupPoint(context.Context, *SetPickupPointRequest) (*CartMutationReply, error)
+	// (Checkout RPC removed - handled externally)
+	SetCartItems(context.Context, *SetCartItemsRequest) (*CartMutationReply, error)
+	OrderCompleted(context.Context, *OrderCompletedRequest) (*CartMutationReply, error)
 	GetState(context.Context, *StateRequest) (*StateReply, error)
 	mustEmbedUnimplementedCartActorServer()
 }
@@ -83,8 +189,32 @@ type CartActorServer interface {
 // pointer dereference when methods are called.
 type UnimplementedCartActorServer struct{}
 
-func (UnimplementedCartActorServer) Mutate(context.Context, *MutationRequest) (*MutationReply, error) {
+func (UnimplementedCartActorServer) AddRequest(context.Context, *AddRequestRequest) (*CartMutationReply, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method Mutate not implemented")
+	return nil, status.Errorf(codes.Unimplemented, "method AddRequest not implemented")
+}
+func (UnimplementedCartActorServer) AddItem(context.Context, *AddItemRequest) (*CartMutationReply, error) {
+	return nil, status.Errorf(codes.Unimplemented, "method AddItem not implemented")
+}
+func (UnimplementedCartActorServer) RemoveItem(context.Context, *RemoveItemRequest) (*CartMutationReply, error) {
+	return nil, status.Errorf(codes.Unimplemented, "method RemoveItem not implemented")
+}
+func (UnimplementedCartActorServer) RemoveDelivery(context.Context, *RemoveDeliveryRequest) (*CartMutationReply, error) {
+	return nil, status.Errorf(codes.Unimplemented, "method RemoveDelivery not implemented")
+}
+func (UnimplementedCartActorServer) ChangeQuantity(context.Context, *ChangeQuantityRequest) (*CartMutationReply, error) {
+	return nil, status.Errorf(codes.Unimplemented, "method ChangeQuantity not implemented")
+}
+func (UnimplementedCartActorServer) SetDelivery(context.Context, *SetDeliveryRequest) (*CartMutationReply, error) {
+	return nil, status.Errorf(codes.Unimplemented, "method SetDelivery not implemented")
+}
+func (UnimplementedCartActorServer) SetPickupPoint(context.Context, *SetPickupPointRequest) (*CartMutationReply, error) {
+	return nil, status.Errorf(codes.Unimplemented, "method SetPickupPoint not implemented")
+}
+func (UnimplementedCartActorServer) SetCartItems(context.Context, *SetCartItemsRequest) (*CartMutationReply, error) {
+	return nil, status.Errorf(codes.Unimplemented, "method SetCartItems not implemented")
+}
+func (UnimplementedCartActorServer) OrderCompleted(context.Context, *OrderCompletedRequest) (*CartMutationReply, error) {
+	return nil, status.Errorf(codes.Unimplemented, "method OrderCompleted not implemented")
 }
 func (UnimplementedCartActorServer) GetState(context.Context, *StateRequest) (*StateReply, error) {
 	return nil, status.Errorf(codes.Unimplemented, "method GetState not implemented")
@@ -110,20 +240,164 @@ func RegisterCartActorServer(s grpc.ServiceRegistrar, srv CartActorServer) {
 	s.RegisterService(&CartActor_ServiceDesc, srv)
 }
 
-func _CartActor_Mutate_Handler(srv interface{}, ctx context.Context, dec func(interface{}) error, interceptor grpc.UnaryServerInterceptor) (interface{}, error) {
+func _CartActor_AddRequest_Handler(srv interface{}, ctx context.Context, dec func(interface{}) error, interceptor grpc.UnaryServerInterceptor) (interface{}, error) {
-	in := new(MutationRequest)
+	in := new(AddRequestRequest)
 	if err := dec(in); err != nil {
 		return nil, err
 	}
 	if interceptor == nil {
-		return srv.(CartActorServer).Mutate(ctx, in)
+		return srv.(CartActorServer).AddRequest(ctx, in)
 	}
 	info := &grpc.UnaryServerInfo{
 		Server:     srv,
-		FullMethod: CartActor_Mutate_FullMethodName,
+		FullMethod: CartActor_AddRequest_FullMethodName,
 	}
 	handler := func(ctx context.Context, req interface{}) (interface{}, error) {
-		return srv.(CartActorServer).Mutate(ctx, req.(*MutationRequest))
+		return srv.(CartActorServer).AddRequest(ctx, req.(*AddRequestRequest))
+	}
+	return interceptor(ctx, in, info, handler)
+}
+
+func _CartActor_AddItem_Handler(srv interface{}, ctx context.Context, dec func(interface{}) error, interceptor grpc.UnaryServerInterceptor) (interface{}, error) {
+	in := new(AddItemRequest)
+	if err := dec(in); err != nil {
+		return nil, err
+	}
+	if interceptor == nil {
+		return srv.(CartActorServer).AddItem(ctx, in)
+	}
+	info := &grpc.UnaryServerInfo{
+		Server:     srv,
+		FullMethod: CartActor_AddItem_FullMethodName,
+	}
+	handler := func(ctx context.Context, req interface{}) (interface{}, error) {
+		return srv.(CartActorServer).AddItem(ctx, req.(*AddItemRequest))
+	}
+	return interceptor(ctx, in, info, handler)
+}
+
+func _CartActor_RemoveItem_Handler(srv interface{}, ctx context.Context, dec func(interface{}) error, interceptor grpc.UnaryServerInterceptor) (interface{}, error) {
+	in := new(RemoveItemRequest)
+	if err := dec(in); err != nil {
+		return nil, err
+	}
+	if interceptor == nil {
+		return srv.(CartActorServer).RemoveItem(ctx, in)
+	}
+	info := &grpc.UnaryServerInfo{
+		Server:     srv,
+		FullMethod: CartActor_RemoveItem_FullMethodName,
+	}
+	handler := func(ctx context.Context, req interface{}) (interface{}, error) {
+		return srv.(CartActorServer).RemoveItem(ctx, req.(*RemoveItemRequest))
+	}
+	return interceptor(ctx, in, info, handler)
+}
+
+func _CartActor_RemoveDelivery_Handler(srv interface{}, ctx context.Context, dec func(interface{}) error, interceptor grpc.UnaryServerInterceptor) (interface{}, error) {
+	in := new(RemoveDeliveryRequest)
+	if err := dec(in); err != nil {
+		return nil, err
+	}
+	if interceptor == nil {
+		return srv.(CartActorServer).RemoveDelivery(ctx, in)
+	}
+	info := &grpc.UnaryServerInfo{
+		Server:     srv,
+		FullMethod: CartActor_RemoveDelivery_FullMethodName,
+	}
+	handler := func(ctx context.Context, req interface{}) (interface{}, error) {
+		return srv.(CartActorServer).RemoveDelivery(ctx, req.(*RemoveDeliveryRequest))
+	}
+	return interceptor(ctx, in, info, handler)
+}
+
+func _CartActor_ChangeQuantity_Handler(srv interface{}, ctx context.Context, dec func(interface{}) error, interceptor grpc.UnaryServerInterceptor) (interface{}, error) {
+	in := new(ChangeQuantityRequest)
+	if err := dec(in); err != nil {
+		return nil, err
+	}
+	if interceptor == nil {
+		return srv.(CartActorServer).ChangeQuantity(ctx, in)
+	}
+	info := &grpc.UnaryServerInfo{
+		Server:     srv,
+		FullMethod: CartActor_ChangeQuantity_FullMethodName,
+	}
+	handler := func(ctx context.Context, req interface{}) (interface{}, error) {
+		return srv.(CartActorServer).ChangeQuantity(ctx, req.(*ChangeQuantityRequest))
+	}
+	return interceptor(ctx, in, info, handler)
+}
+
+func _CartActor_SetDelivery_Handler(srv interface{}, ctx context.Context, dec func(interface{}) error, interceptor grpc.UnaryServerInterceptor) (interface{}, error) {
+	in := new(SetDeliveryRequest)
+	if err := dec(in); err != nil {
+		return nil, err
+	}
+	if interceptor == nil {
+		return srv.(CartActorServer).SetDelivery(ctx, in)
+	}
+	info := &grpc.UnaryServerInfo{
+		Server:     srv,
+		FullMethod: CartActor_SetDelivery_FullMethodName,
+	}
+	handler := func(ctx context.Context, req interface{}) (interface{}, error) {
+		return srv.(CartActorServer).SetDelivery(ctx, req.(*SetDeliveryRequest))
+	}
+	return interceptor(ctx, in, info, handler)
+}
+
+func _CartActor_SetPickupPoint_Handler(srv interface{}, ctx context.Context, dec func(interface{}) error, interceptor grpc.UnaryServerInterceptor) (interface{}, error) {
+	in := new(SetPickupPointRequest)
+	if err := dec(in); err != nil {
+		return nil, err
+	}
+	if interceptor == nil {
+		return srv.(CartActorServer).SetPickupPoint(ctx, in)
+	}
+	info := &grpc.UnaryServerInfo{
+		Server:     srv,
+		FullMethod: CartActor_SetPickupPoint_FullMethodName,
+	}
+	handler := func(ctx context.Context, req interface{}) (interface{}, error) {
+		return srv.(CartActorServer).SetPickupPoint(ctx, req.(*SetPickupPointRequest))
+	}
+	return interceptor(ctx, in, info, handler)
+}
+
+func _CartActor_SetCartItems_Handler(srv interface{}, ctx context.Context, dec func(interface{}) error, interceptor grpc.UnaryServerInterceptor) (interface{}, error) {
+	in := new(SetCartItemsRequest)
+	if err := dec(in); err != nil {
+		return nil, err
+	}
+	if interceptor == nil {
+		return srv.(CartActorServer).SetCartItems(ctx, in)
+	}
+	info := &grpc.UnaryServerInfo{
+		Server:     srv,
+		FullMethod: CartActor_SetCartItems_FullMethodName,
+	}
+	handler := func(ctx context.Context, req interface{}) (interface{}, error) {
+		return srv.(CartActorServer).SetCartItems(ctx, req.(*SetCartItemsRequest))
+	}
+	return interceptor(ctx, in, info, handler)
+}
+
+func _CartActor_OrderCompleted_Handler(srv interface{}, ctx context.Context, dec func(interface{}) error, interceptor grpc.UnaryServerInterceptor) (interface{}, error) {
+	in := new(OrderCompletedRequest)
+	if err := dec(in); err != nil {
+		return nil, err
+	}
+	if interceptor == nil {
+		return srv.(CartActorServer).OrderCompleted(ctx, in)
+	}
+	info := &grpc.UnaryServerInfo{
+		Server:     srv,
+		FullMethod: CartActor_OrderCompleted_FullMethodName,
+	}
+	handler := func(ctx context.Context, req interface{}) (interface{}, error) {
+		return srv.(CartActorServer).OrderCompleted(ctx, req.(*OrderCompletedRequest))
 	}
 	return interceptor(ctx, in, info, handler)
 }
@@ -154,8 +428,40 @@ var CartActor_ServiceDesc = grpc.ServiceDesc{
 	HandlerType: (*CartActorServer)(nil),
 	Methods: []grpc.MethodDesc{
 		{
-			MethodName: "Mutate",
+			MethodName: "AddRequest",
-			Handler:    _CartActor_Mutate_Handler,
+			Handler:    _CartActor_AddRequest_Handler,
+		},
+		{
+			MethodName: "AddItem",
+			Handler:    _CartActor_AddItem_Handler,
+		},
+		{
+			MethodName: "RemoveItem",
+			Handler:    _CartActor_RemoveItem_Handler,
+		},
+		{
+			MethodName: "RemoveDelivery",
+			Handler:    _CartActor_RemoveDelivery_Handler,
+		},
+		{
+			MethodName: "ChangeQuantity",
+			Handler:    _CartActor_ChangeQuantity_Handler,
+		},
+		{
+			MethodName: "SetDelivery",
+			Handler:    _CartActor_SetDelivery_Handler,
+		},
+		{
+			MethodName: "SetPickupPoint",
+			Handler:    _CartActor_SetPickupPoint_Handler,
+		},
+		{
+			MethodName: "SetCartItems",
+			Handler:    _CartActor_SetCartItems_Handler,
+		},
+		{
+			MethodName: "OrderCompleted",
+			Handler:    _CartActor_OrderCompleted_Handler,
 		},
 		{
 			MethodName: "GetState",

proto/control_plane.pb.go

@@ -246,60 +246,7 @@ func (x *CartIdsReply) GetCartIds() []string {
 	return nil
 }
 
-// OwnerChangeRequest notifies peers that ownership of a cart moved (or is moving) to new_host.
+// OwnerChangeAck retained as response type for Closing RPC (ConfirmOwner removed).
-type OwnerChangeRequest struct {
-	state         protoimpl.MessageState `protogen:"open.v1"`
-	CartId        string                 `protobuf:"bytes,1,opt,name=cart_id,json=cartId,proto3" json:"cart_id,omitempty"`
-	NewHost       string                 `protobuf:"bytes,2,opt,name=new_host,json=newHost,proto3" json:"new_host,omitempty"`
-	unknownFields protoimpl.UnknownFields
-	sizeCache     protoimpl.SizeCache
-}
-
-func (x *OwnerChangeRequest) Reset() {
-	*x = OwnerChangeRequest{}
-	mi := &file_control_plane_proto_msgTypes[5]
-	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
-	ms.StoreMessageInfo(mi)
-}
-
-func (x *OwnerChangeRequest) String() string {
-	return protoimpl.X.MessageStringOf(x)
-}
-
-func (*OwnerChangeRequest) ProtoMessage() {}
-
-func (x *OwnerChangeRequest) ProtoReflect() protoreflect.Message {
-	mi := &file_control_plane_proto_msgTypes[5]
-	if x != nil {
-		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
-		if ms.LoadMessageInfo() == nil {
-			ms.StoreMessageInfo(mi)
-		}
-		return ms
-	}
-	return mi.MessageOf(x)
-}
-
-// Deprecated: Use OwnerChangeRequest.ProtoReflect.Descriptor instead.
-func (*OwnerChangeRequest) Descriptor() ([]byte, []int) {
-	return file_control_plane_proto_rawDescGZIP(), []int{5}
-}
-
-func (x *OwnerChangeRequest) GetCartId() string {
-	if x != nil {
-		return x.CartId
-	}
-	return ""
-}
-
-func (x *OwnerChangeRequest) GetNewHost() string {
-	if x != nil {
-		return x.NewHost
-	}
-	return ""
-}
-
-// OwnerChangeAck indicates acceptance or rejection of an ownership change.
 type OwnerChangeAck struct {
 	state         protoimpl.MessageState `protogen:"open.v1"`
 	Accepted      bool                   `protobuf:"varint,1,opt,name=accepted,proto3" json:"accepted,omitempty"`
@@ -310,7 +257,7 @@ type OwnerChangeAck struct {
 
 func (x *OwnerChangeAck) Reset() {
 	*x = OwnerChangeAck{}
-	mi := &file_control_plane_proto_msgTypes[6]
+	mi := &file_control_plane_proto_msgTypes[5]
 	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 	ms.StoreMessageInfo(mi)
 }
@@ -322,7 +269,7 @@ func (x *OwnerChangeAck) String() string {
 func (*OwnerChangeAck) ProtoMessage() {}
 
 func (x *OwnerChangeAck) ProtoReflect() protoreflect.Message {
-	mi := &file_control_plane_proto_msgTypes[6]
+	mi := &file_control_plane_proto_msgTypes[5]
 	if x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -335,7 +282,7 @@ func (x *OwnerChangeAck) ProtoReflect() protoreflect.Message {
 
 // Deprecated: Use OwnerChangeAck.ProtoReflect.Descriptor instead.
 func (*OwnerChangeAck) Descriptor() ([]byte, []int) {
-	return file_control_plane_proto_rawDescGZIP(), []int{6}
+	return file_control_plane_proto_rawDescGZIP(), []int{5}
 }
 
 func (x *OwnerChangeAck) GetAccepted() bool {
@@ -362,7 +309,7 @@ type ClosingNotice struct {
 
 func (x *ClosingNotice) Reset() {
 	*x = ClosingNotice{}
-	mi := &file_control_plane_proto_msgTypes[7]
+	mi := &file_control_plane_proto_msgTypes[6]
 	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 	ms.StoreMessageInfo(mi)
 }
@@ -374,7 +321,7 @@ func (x *ClosingNotice) String() string {
 func (*ClosingNotice) ProtoMessage() {}
 
 func (x *ClosingNotice) ProtoReflect() protoreflect.Message {
-	mi := &file_control_plane_proto_msgTypes[7]
+	mi := &file_control_plane_proto_msgTypes[6]
 	if x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -387,7 +334,7 @@ func (x *ClosingNotice) ProtoReflect() protoreflect.Message {
 
 // Deprecated: Use ClosingNotice.ProtoReflect.Descriptor instead.
 func (*ClosingNotice) Descriptor() ([]byte, []int) {
-	return file_control_plane_proto_rawDescGZIP(), []int{7}
+	return file_control_plane_proto_rawDescGZIP(), []int{6}
 }
 
 func (x *ClosingNotice) GetHost() string {
@@ -412,23 +359,18 @@ const file_control_plane_proto_rawDesc = "" +
 	"\x0eNegotiateReply\x12\x14\n" +
 	"\x05hosts\x18\x01 \x03(\tR\x05hosts\")\n" +
 	"\fCartIdsReply\x12\x19\n" +
-	"\bcart_ids\x18\x01 \x03(\tR\acartIds\"H\n" +
+	"\bcart_ids\x18\x01 \x03(\tR\acartIds\"F\n" +
-	"\x12OwnerChangeRequest\x12\x17\n" +
-	"\acart_id\x18\x01 \x01(\tR\x06cartId\x12\x19\n" +
-	"\bnew_host\x18\x02 \x01(\tR\anewHost\"F\n" +
 	"\x0eOwnerChangeAck\x12\x1a\n" +
 	"\baccepted\x18\x01 \x01(\bR\baccepted\x12\x18\n" +
 	"\amessage\x18\x02 \x01(\tR\amessage\"#\n" +
 	"\rClosingNotice\x12\x12\n" +
-	"\x04host\x18\x01 \x01(\tR\x04host2\xbc\x02\n" +
+	"\x04host\x18\x01 \x01(\tR\x04host2\xf4\x01\n" +
 	"\fControlPlane\x12,\n" +
 	"\x04Ping\x12\x0f.messages.Empty\x1a\x13.messages.PingReply\x12A\n" +
 	"\tNegotiate\x12\x1a.messages.NegotiateRequest\x1a\x18.messages.NegotiateReply\x125\n" +
 	"\n" +
-	"GetCartIds\x12\x0f.messages.Empty\x1a\x16.messages.CartIdsReply\x12F\n" +
+	"GetCartIds\x12\x0f.messages.Empty\x1a\x16.messages.CartIdsReply\x12<\n" +
-	"\fConfirmOwner\x12\x1c.messages.OwnerChangeRequest\x1a\x18.messages.OwnerChangeAck\x12<\n" +
+	"\aClosing\x12\x17.messages.ClosingNotice\x1a\x18.messages.OwnerChangeAckB.Z,git.tornberg.me/go-cart-actor/proto;messagesb\x06proto3"
-	"\aClosing\x12\x17.messages.ClosingNotice\x1a\x18.messages.OwnerChangeAckB\fZ\n" +
-	".;messagesb\x06proto3"
 
 var (
 	file_control_plane_proto_rawDescOnce sync.Once
@@ -442,30 +384,27 @@ func file_control_plane_proto_rawDescGZIP() []byte {
 	return file_control_plane_proto_rawDescData
 }
 
-var file_control_plane_proto_msgTypes = make([]protoimpl.MessageInfo, 8)
+var file_control_plane_proto_msgTypes = make([]protoimpl.MessageInfo, 7)
 var file_control_plane_proto_goTypes = []any{
-	(*Empty)(nil),              // 0: messages.Empty
+	(*Empty)(nil),            // 0: messages.Empty
-	(*PingReply)(nil),          // 1: messages.PingReply
+	(*PingReply)(nil),        // 1: messages.PingReply
-	(*NegotiateRequest)(nil),   // 2: messages.NegotiateRequest
+	(*NegotiateRequest)(nil), // 2: messages.NegotiateRequest
-	(*NegotiateReply)(nil),     // 3: messages.NegotiateReply
+	(*NegotiateReply)(nil),   // 3: messages.NegotiateReply
-	(*CartIdsReply)(nil),       // 4: messages.CartIdsReply
+	(*CartIdsReply)(nil),     // 4: messages.CartIdsReply
-	(*OwnerChangeRequest)(nil), // 5: messages.OwnerChangeRequest
+	(*OwnerChangeAck)(nil),   // 5: messages.OwnerChangeAck
-	(*OwnerChangeAck)(nil),     // 6: messages.OwnerChangeAck
+	(*ClosingNotice)(nil),    // 6: messages.ClosingNotice
-	(*ClosingNotice)(nil),      // 7: messages.ClosingNotice
 }
 var file_control_plane_proto_depIdxs = []int32{
 	0, // 0: messages.ControlPlane.Ping:input_type -> messages.Empty
 	2, // 1: messages.ControlPlane.Negotiate:input_type -> messages.NegotiateRequest
 	0, // 2: messages.ControlPlane.GetCartIds:input_type -> messages.Empty
-	5, // 3: messages.ControlPlane.ConfirmOwner:input_type -> messages.OwnerChangeRequest
+	6, // 3: messages.ControlPlane.Closing:input_type -> messages.ClosingNotice
-	7, // 4: messages.ControlPlane.Closing:input_type -> messages.ClosingNotice
+	1, // 4: messages.ControlPlane.Ping:output_type -> messages.PingReply
-	1, // 5: messages.ControlPlane.Ping:output_type -> messages.PingReply
+	3, // 5: messages.ControlPlane.Negotiate:output_type -> messages.NegotiateReply
-	3, // 6: messages.ControlPlane.Negotiate:output_type -> messages.NegotiateReply
+	4, // 6: messages.ControlPlane.GetCartIds:output_type -> messages.CartIdsReply
-	4, // 7: messages.ControlPlane.GetCartIds:output_type -> messages.CartIdsReply
+	5, // 7: messages.ControlPlane.Closing:output_type -> messages.OwnerChangeAck
-	6, // 8: messages.ControlPlane.ConfirmOwner:output_type -> messages.OwnerChangeAck
+	4, // [4:8] is the sub-list for method output_type
-	6, // 9: messages.ControlPlane.Closing:output_type -> messages.OwnerChangeAck
+	0, // [0:4] is the sub-list for method input_type
-	5, // [5:10] is the sub-list for method output_type
-	0, // [0:5] is the sub-list for method input_type
 	0, // [0:0] is the sub-list for extension type_name
 	0, // [0:0] is the sub-list for extension extendee
 	0, // [0:0] is the sub-list for field type_name
@@ -482,7 +421,7 @@ func file_control_plane_proto_init() {
 			GoPackagePath: reflect.TypeOf(x{}).PkgPath(),
 			RawDescriptor: unsafe.Slice(unsafe.StringData(file_control_plane_proto_rawDesc), len(file_control_plane_proto_rawDesc)),
 			NumEnums:      0,
-			NumMessages:   8,
+			NumMessages:   7,
 			NumExtensions: 0,
 			NumServices:   1,
 		},

proto/control_plane.proto

@@ -2,7 +2,7 @@ syntax = "proto3";
 
 package messages;
 
-option go_package = ".;messages";
+option go_package = "git.tornberg.me/go-cart-actor/proto;messages";
 
 // -----------------------------------------------------------------------------
 // Control Plane gRPC API
@@ -11,7 +11,7 @@ option go_package = ".;messages";
 // Responsibilities:
 //   - Liveness (Ping)
 //   - Membership negotiation (Negotiate)
-//   - Cart ownership change propagation (ConfirmOwner)
+//   - Deterministic ring-based ownership (ConfirmOwner RPC removed)
 //   - Cart ID listing for remote grain spawning (GetCartIds)
 //   - Graceful shutdown notifications (Closing)
 // No authentication / TLS is defined initially (can be added later).
@@ -41,13 +41,7 @@ message CartIdsReply {
   repeated string cart_ids = 1;
 }
 
-// OwnerChangeRequest notifies peers that ownership of a cart moved (or is moving) to new_host.
+// OwnerChangeAck retained as response type for Closing RPC (ConfirmOwner removed).
-message OwnerChangeRequest {
-  string cart_id = 1;
-  string new_host = 2;
-}
-
-// OwnerChangeAck indicates acceptance or rejection of an ownership change.
 message OwnerChangeAck {
   bool accepted = 1;
   string message = 2;
@@ -69,8 +63,7 @@ service ControlPlane {
   // GetCartIds lists currently owned cart IDs on this node.
   rpc GetCartIds(Empty) returns (CartIdsReply);
 
-  // ConfirmOwner announces/asks peers to acknowledge ownership transfer.
+  // ConfirmOwner RPC removed (was legacy ownership acknowledgement; ring-based ownership now authoritative)
-  rpc ConfirmOwner(OwnerChangeRequest) returns (OwnerChangeAck);
 
   // Closing announces graceful shutdown so peers can proactively adjust.
   rpc Closing(ClosingNotice) returns (OwnerChangeAck);

proto/control_plane_grpc.pb.go

@@ -19,11 +19,10 @@ import (
 const _ = grpc.SupportPackageIsVersion9
 
 const (
-	ControlPlane_Ping_FullMethodName         = "/messages.ControlPlane/Ping"
+	ControlPlane_Ping_FullMethodName       = "/messages.ControlPlane/Ping"
-	ControlPlane_Negotiate_FullMethodName    = "/messages.ControlPlane/Negotiate"
+	ControlPlane_Negotiate_FullMethodName  = "/messages.ControlPlane/Negotiate"
-	ControlPlane_GetCartIds_FullMethodName   = "/messages.ControlPlane/GetCartIds"
+	ControlPlane_GetCartIds_FullMethodName = "/messages.ControlPlane/GetCartIds"
-	ControlPlane_ConfirmOwner_FullMethodName = "/messages.ControlPlane/ConfirmOwner"
+	ControlPlane_Closing_FullMethodName    = "/messages.ControlPlane/Closing"
-	ControlPlane_Closing_FullMethodName      = "/messages.ControlPlane/Closing"
 )
 
 // ControlPlaneClient is the client API for ControlPlane service.
@@ -38,8 +37,6 @@ type ControlPlaneClient interface {
 	Negotiate(ctx context.Context, in *NegotiateRequest, opts ...grpc.CallOption) (*NegotiateReply, error)
 	// GetCartIds lists currently owned cart IDs on this node.
 	GetCartIds(ctx context.Context, in *Empty, opts ...grpc.CallOption) (*CartIdsReply, error)
-	// ConfirmOwner announces/asks peers to acknowledge ownership transfer.
-	ConfirmOwner(ctx context.Context, in *OwnerChangeRequest, opts ...grpc.CallOption) (*OwnerChangeAck, error)
 	// Closing announces graceful shutdown so peers can proactively adjust.
 	Closing(ctx context.Context, in *ClosingNotice, opts ...grpc.CallOption) (*OwnerChangeAck, error)
 }
@@ -82,16 +79,6 @@ func (c *controlPlaneClient) GetCartIds(ctx context.Context, in *Empty, opts ...
 	return out, nil
 }
 
-func (c *controlPlaneClient) ConfirmOwner(ctx context.Context, in *OwnerChangeRequest, opts ...grpc.CallOption) (*OwnerChangeAck, error) {
-	cOpts := append([]grpc.CallOption{grpc.StaticMethod()}, opts...)
-	out := new(OwnerChangeAck)
-	err := c.cc.Invoke(ctx, ControlPlane_ConfirmOwner_FullMethodName, in, out, cOpts...)
-	if err != nil {
-		return nil, err
-	}
-	return out, nil
-}
-
 func (c *controlPlaneClient) Closing(ctx context.Context, in *ClosingNotice, opts ...grpc.CallOption) (*OwnerChangeAck, error) {
 	cOpts := append([]grpc.CallOption{grpc.StaticMethod()}, opts...)
 	out := new(OwnerChangeAck)
@@ -114,8 +101,6 @@ type ControlPlaneServer interface {
 	Negotiate(context.Context, *NegotiateRequest) (*NegotiateReply, error)
 	// GetCartIds lists currently owned cart IDs on this node.
 	GetCartIds(context.Context, *Empty) (*CartIdsReply, error)
-	// ConfirmOwner announces/asks peers to acknowledge ownership transfer.
-	ConfirmOwner(context.Context, *OwnerChangeRequest) (*OwnerChangeAck, error)
 	// Closing announces graceful shutdown so peers can proactively adjust.
 	Closing(context.Context, *ClosingNotice) (*OwnerChangeAck, error)
 	mustEmbedUnimplementedControlPlaneServer()
@@ -137,9 +122,6 @@ func (UnimplementedControlPlaneServer) Negotiate(context.Context, *NegotiateRequ
 func (UnimplementedControlPlaneServer) GetCartIds(context.Context, *Empty) (*CartIdsReply, error) {
 	return nil, status.Errorf(codes.Unimplemented, "method GetCartIds not implemented")
 }
-func (UnimplementedControlPlaneServer) ConfirmOwner(context.Context, *OwnerChangeRequest) (*OwnerChangeAck, error) {
-	return nil, status.Errorf(codes.Unimplemented, "method ConfirmOwner not implemented")
-}
 func (UnimplementedControlPlaneServer) Closing(context.Context, *ClosingNotice) (*OwnerChangeAck, error) {
 	return nil, status.Errorf(codes.Unimplemented, "method Closing not implemented")
 }
@@ -218,24 +200,6 @@ func _ControlPlane_GetCartIds_Handler(srv interface{}, ctx context.Context, dec
 	return interceptor(ctx, in, info, handler)
 }
 
-func _ControlPlane_ConfirmOwner_Handler(srv interface{}, ctx context.Context, dec func(interface{}) error, interceptor grpc.UnaryServerInterceptor) (interface{}, error) {
-	in := new(OwnerChangeRequest)
-	if err := dec(in); err != nil {
-		return nil, err
-	}
-	if interceptor == nil {
-		return srv.(ControlPlaneServer).ConfirmOwner(ctx, in)
-	}
-	info := &grpc.UnaryServerInfo{
-		Server:     srv,
-		FullMethod: ControlPlane_ConfirmOwner_FullMethodName,
-	}
-	handler := func(ctx context.Context, req interface{}) (interface{}, error) {
-		return srv.(ControlPlaneServer).ConfirmOwner(ctx, req.(*OwnerChangeRequest))
-	}
-	return interceptor(ctx, in, info, handler)
-}
-
 func _ControlPlane_Closing_Handler(srv interface{}, ctx context.Context, dec func(interface{}) error, interceptor grpc.UnaryServerInterceptor) (interface{}, error) {
 	in := new(ClosingNotice)
 	if err := dec(in); err != nil {
@@ -273,10 +237,6 @@ var ControlPlane_ServiceDesc = grpc.ServiceDesc{
 			MethodName: "GetCartIds",
 			Handler:    _ControlPlane_GetCartIds_Handler,
 		},
-		{
-			MethodName: "ConfirmOwner",
-			Handler:    _ControlPlane_ConfirmOwner_Handler,
-		},
 		{
 			MethodName: "Closing",
 			Handler:    _ControlPlane_Closing_Handler,

proto/messages.pb.go

@@ -889,6 +889,102 @@ func (x *OrderCreated) GetStatus() string {
 	return ""
 }
 
+type Noop struct {
+	state         protoimpl.MessageState `protogen:"open.v1"`
+	unknownFields protoimpl.UnknownFields
+	sizeCache     protoimpl.SizeCache
+}
+
+func (x *Noop) Reset() {
+	*x = Noop{}
+	mi := &file_messages_proto_msgTypes[11]
+	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+	ms.StoreMessageInfo(mi)
+}
+
+func (x *Noop) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*Noop) ProtoMessage() {}
+
+func (x *Noop) ProtoReflect() protoreflect.Message {
+	mi := &file_messages_proto_msgTypes[11]
+	if x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use Noop.ProtoReflect.Descriptor instead.
+func (*Noop) Descriptor() ([]byte, []int) {
+	return file_messages_proto_rawDescGZIP(), []int{11}
+}
+
+type InitializeCheckout struct {
+	state             protoimpl.MessageState `protogen:"open.v1"`
+	OrderId           string                 `protobuf:"bytes,1,opt,name=orderId,proto3" json:"orderId,omitempty"`
+	Status            string                 `protobuf:"bytes,2,opt,name=status,proto3" json:"status,omitempty"`
+	PaymentInProgress bool                   `protobuf:"varint,3,opt,name=paymentInProgress,proto3" json:"paymentInProgress,omitempty"`
+	unknownFields     protoimpl.UnknownFields
+	sizeCache         protoimpl.SizeCache
+}
+
+func (x *InitializeCheckout) Reset() {
+	*x = InitializeCheckout{}
+	mi := &file_messages_proto_msgTypes[12]
+	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+	ms.StoreMessageInfo(mi)
+}
+
+func (x *InitializeCheckout) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*InitializeCheckout) ProtoMessage() {}
+
+func (x *InitializeCheckout) ProtoReflect() protoreflect.Message {
+	mi := &file_messages_proto_msgTypes[12]
+	if x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use InitializeCheckout.ProtoReflect.Descriptor instead.
+func (*InitializeCheckout) Descriptor() ([]byte, []int) {
+	return file_messages_proto_rawDescGZIP(), []int{12}
+}
+
+func (x *InitializeCheckout) GetOrderId() string {
+	if x != nil {
+		return x.OrderId
+	}
+	return ""
+}
+
+func (x *InitializeCheckout) GetStatus() string {
+	if x != nil {
+		return x.Status
+	}
+	return ""
+}
+
+func (x *InitializeCheckout) GetPaymentInProgress() bool {
+	if x != nil {
+		return x.PaymentInProgress
+	}
+	return false
+}
+
 var File_messages_proto protoreflect.FileDescriptor
 
 const file_messages_proto_rawDesc = "" +
@@ -997,8 +1093,12 @@ const file_messages_proto_rawDesc = "" +
 	"\acountry\x18\x06 \x01(\tR\acountry\"@\n" +
 	"\fOrderCreated\x12\x18\n" +
 	"\aorderId\x18\x01 \x01(\tR\aorderId\x12\x16\n" +
-	"\x06status\x18\x02 \x01(\tR\x06statusB\fZ\n" +
+	"\x06status\x18\x02 \x01(\tR\x06status\"\x06\n" +
-	".;messagesb\x06proto3"
+	"\x04Noop\"t\n" +
+	"\x12InitializeCheckout\x12\x18\n" +
+	"\aorderId\x18\x01 \x01(\tR\aorderId\x12\x16\n" +
+	"\x06status\x18\x02 \x01(\tR\x06status\x12,\n" +
+	"\x11paymentInProgress\x18\x03 \x01(\bR\x11paymentInProgressB.Z,git.tornberg.me/go-cart-actor/proto;messagesb\x06proto3"
 
 var (
 	file_messages_proto_rawDescOnce sync.Once
@@ -1012,7 +1112,7 @@ func file_messages_proto_rawDescGZIP() []byte {
 	return file_messages_proto_rawDescData
 }
 
-var file_messages_proto_msgTypes = make([]protoimpl.MessageInfo, 11)
+var file_messages_proto_msgTypes = make([]protoimpl.MessageInfo, 13)
 var file_messages_proto_goTypes = []any{
 	(*AddRequest)(nil),          // 0: messages.AddRequest
 	(*SetCartRequest)(nil),      // 1: messages.SetCartRequest
@@ -1025,6 +1125,8 @@ var file_messages_proto_goTypes = []any{
 	(*RemoveDelivery)(nil),      // 8: messages.RemoveDelivery
 	(*CreateCheckoutOrder)(nil), // 9: messages.CreateCheckoutOrder
 	(*OrderCreated)(nil),        // 10: messages.OrderCreated
+	(*Noop)(nil),                // 11: messages.Noop
+	(*InitializeCheckout)(nil),  // 12: messages.InitializeCheckout
 }
 var file_messages_proto_depIdxs = []int32{
 	0, // 0: messages.SetCartRequest.items:type_name -> messages.AddRequest
@@ -1052,7 +1154,7 @@ func file_messages_proto_init() {
 			GoPackagePath: reflect.TypeOf(x{}).PkgPath(),
 			RawDescriptor: unsafe.Slice(unsafe.StringData(file_messages_proto_rawDesc), len(file_messages_proto_rawDesc)),
 			NumEnums:      0,
-			NumMessages:   11,
+			NumMessages:   13,
 			NumExtensions: 0,
 			NumServices:   0,
 		},

proto/messages.proto

@@ -1,6 +1,6 @@
 syntax = "proto3";
 package messages;
-option go_package = ".;messages";
+option go_package = "git.tornberg.me/go-cart-actor/proto;messages";
 
 message AddRequest {
 		int32 quantity = 1;
@@ -93,3 +93,13 @@ message OrderCreated {
 		string orderId = 1;
 		string status = 2;
 }
+
+message Noop {
+		// Intentionally empty - used for ownership acquisition or health pings
+}
+
+message InitializeCheckout {
+        string orderId = 1;
+        string status = 2;
+        bool paymentInProgress = 3;
+}

remote-grain-pool._go

@@ -1,67 +0,0 @@
-// package main
-
-// import "sync"
-
-// type RemoteGrainPool struct {
-// 	mu     sync.RWMutex
-// 	Host   string
-// 	grains map[CartId]*RemoteGrain
-// }
-
-// func NewRemoteGrainPool(addr string) *RemoteGrainPool {
-// 	return &RemoteGrainPool{
-// 		Host:   addr,
-// 		grains: make(map[CartId]*RemoteGrain),
-// 	}
-// }
-
-// func (p *RemoteGrainPool) findRemoteGrain(id CartId) *RemoteGrain {
-// 	p.mu.RLock()
-// 	grain, ok := p.grains[id]
-// 	p.mu.RUnlock()
-// 	if !ok {
-// 		return nil
-// 	}
-// 	return grain
-// }
-
-// func (p *RemoteGrainPool) findOrCreateGrain(id CartId) (*RemoteGrain, error) {
-// 	grain := p.findRemoteGrain(id)
-
-// 	if grain == nil {
-// 		grain, err := NewRemoteGrain(id, p.Host)
-// 		if err != nil {
-// 			return nil, err
-// 		}
-// 		p.mu.Lock()
-// 		p.grains[id] = grain
-// 		p.mu.Unlock()
-// 	}
-// 	return grain, nil
-// }
-
-// func (p *RemoteGrainPool) Delete(id CartId) {
-// 	p.mu.Lock()
-// 	delete(p.grains, id)
-// 	p.mu.Unlock()
-// }
-
-// func (p *RemoteGrainPool) Process(id CartId, messages ...Message) (*FrameWithPayload, error) {
-// 	var result *FrameWithPayload
-// 	grain, err := p.findOrCreateGrain(id)
-// 	if err != nil {
-// 		return nil, err
-// 	}
-// 	for _, message := range messages {
-// 		result, err = grain.HandleMessage(&message, false)
-// 	}
-// 	return result, err
-// }
-
-// func (p *RemoteGrainPool) Get(id CartId) (*FrameWithPayload, error) {
-// 	grain, err := p.findOrCreateGrain(id)
-// 	if err != nil {
-// 		return nil, err
-// 	}
-// 	return grain.GetCurrentState()
-// }

remote_grain_grpc.go

@@ -1,7 +1,6 @@
 package main
 
 import (
-	"bytes"
 	"context"
 	"fmt"
 	"log"
@@ -68,69 +67,264 @@ func (g *RemoteGrainGRPC) GetId() CartId {
 	return g.Id
 }
 
-// HandleMessage serializes the underlying mutation proto (without legacy message header)
+// Apply executes a cart mutation via per-mutation RPCs (breaking v2 API)
-// and invokes the CartActor.Mutate RPC. It wraps the reply into a FrameWithPayload
+// and returns a *CartGrain reconstructed from the CartMutationReply state.
-// for compatibility with existing higher-level code paths.
+func (g *RemoteGrainGRPC) Apply(content interface{}, isReplay bool) (*CartGrain, error) {
-func (g *RemoteGrainGRPC) HandleMessage(message *Message, isReplay bool) (*FrameWithPayload, error) {
-	if message == nil {
-		return nil, fmt.Errorf("nil message")
-	}
 	if isReplay {
-		// Remote replay not expected; ignore to keep parity with old implementation.
 		return nil, fmt.Errorf("replay not supported for remote grains")
 	}
-
+	if content == nil {
-	handler, err := GetMessageHandler(message.Type)
+		return nil, fmt.Errorf("nil mutation content")
-	if err != nil {
-		return nil, err
 	}
 
-	// Ensure timestamp set (legacy behavior)
+	ts := time.Now().Unix()
-	if message.TimeStamp == nil {
+
-		ts := time.Now().Unix()
+	var invoke func(ctx context.Context) (*proto.CartMutationReply, error)
-		message.TimeStamp = &ts
+
+	switch m := content.(type) {
+	case *proto.AddRequest:
+		invoke = func(ctx context.Context) (*proto.CartMutationReply, error) {
+			return g.client.AddRequest(ctx, &proto.AddRequestRequest{
+				CartId:          g.Id.String(),
+				ClientTimestamp: ts,
+				Payload:         m,
+			})
+		}
+	case *proto.AddItem:
+		invoke = func(ctx context.Context) (*proto.CartMutationReply, error) {
+			return g.client.AddItem(ctx, &proto.AddItemRequest{
+				CartId:          g.Id.String(),
+				ClientTimestamp: ts,
+				Payload:         m,
+			})
+		}
+	case *proto.RemoveItem:
+		invoke = func(ctx context.Context) (*proto.CartMutationReply, error) {
+			return g.client.RemoveItem(ctx, &proto.RemoveItemRequest{
+				CartId:          g.Id.String(),
+				ClientTimestamp: ts,
+				Payload:         m,
+			})
+		}
+	case *proto.RemoveDelivery:
+		invoke = func(ctx context.Context) (*proto.CartMutationReply, error) {
+			return g.client.RemoveDelivery(ctx, &proto.RemoveDeliveryRequest{
+				CartId:          g.Id.String(),
+				ClientTimestamp: ts,
+				Payload:         m,
+			})
+		}
+	case *proto.ChangeQuantity:
+		invoke = func(ctx context.Context) (*proto.CartMutationReply, error) {
+			return g.client.ChangeQuantity(ctx, &proto.ChangeQuantityRequest{
+				CartId:          g.Id.String(),
+				ClientTimestamp: ts,
+				Payload:         m,
+			})
+		}
+	case *proto.SetDelivery:
+		invoke = func(ctx context.Context) (*proto.CartMutationReply, error) {
+			return g.client.SetDelivery(ctx, &proto.SetDeliveryRequest{
+				CartId:          g.Id.String(),
+				ClientTimestamp: ts,
+				Payload:         m,
+			})
+		}
+	case *proto.SetPickupPoint:
+		invoke = func(ctx context.Context) (*proto.CartMutationReply, error) {
+			return g.client.SetPickupPoint(ctx, &proto.SetPickupPointRequest{
+				CartId:          g.Id.String(),
+				ClientTimestamp: ts,
+				Payload:         m,
+			})
+		}
+	case *proto.CreateCheckoutOrder:
+		return nil, fmt.Errorf("CreateCheckoutOrder deprecated: checkout is handled via HTTP endpoint (HandleCheckout)")
+	case *proto.SetCartRequest:
+		invoke = func(ctx context.Context) (*proto.CartMutationReply, error) {
+			return g.client.SetCartItems(ctx, &proto.SetCartItemsRequest{
+				CartId:          g.Id.String(),
+				ClientTimestamp: ts,
+				Payload:         m,
+			})
+		}
+	case *proto.OrderCreated:
+		invoke = func(ctx context.Context) (*proto.CartMutationReply, error) {
+			return g.client.OrderCompleted(ctx, &proto.OrderCompletedRequest{
+				CartId:          g.Id.String(),
+				ClientTimestamp: ts,
+				Payload:         m,
+			})
+		}
+	default:
+		return nil, fmt.Errorf("unsupported mutation type %T", content)
 	}
 
-	// Marshal underlying proto payload only (no StorableMessageHeader)
+	if invoke == nil {
-	var buf bytes.Buffer
+		return nil, fmt.Errorf("no invocation mapped for mutation %T", content)
-	err = handler.Write(message, &buf)
-	if err != nil {
-		return nil, fmt.Errorf("encode mutation payload: %w", err)
-	}
-
-	req := &proto.MutationRequest{
-		CartId:          g.Id.String(),
-		Type:            proto.MutationType(message.Type), // numeric mapping preserved
-		Payload:         buf.Bytes(),
-		ClientTimestamp: *message.TimeStamp,
 	}
 
 	ctx, cancel := context.WithTimeout(context.Background(), g.mutateTimeout)
 	defer cancel()
 
-	resp, err := g.client.Mutate(ctx, req)
+	resp, err := invoke(ctx)
 	if err != nil {
 		return nil, err
 	}
 
-	frame := MakeFrameWithPayload(RemoteHandleMutationReply, StatusCode(resp.StatusCode), resp.Payload)
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
-	return &frame, nil
+		if e := resp.GetError(); e != "" {
+			return nil, fmt.Errorf("remote mutation failed %d: %s", resp.StatusCode, e)
+		}
+		return nil, fmt.Errorf("remote mutation failed %d", resp.StatusCode)
+	}
+	state := resp.GetState()
+	if state == nil {
+		return nil, fmt.Errorf("mutation reply missing state on success")
+	}
+	// Reconstruct a lightweight CartGrain (only fields we expose internally)
+	grain := &CartGrain{
+		Id:                ToCartId(state.Id),
+		TotalPrice:        state.TotalPrice,
+		TotalTax:          state.TotalTax,
+		TotalDiscount:     state.TotalDiscount,
+		PaymentInProgress: state.PaymentInProgress,
+		OrderReference:    state.OrderReference,
+		PaymentStatus:     state.PaymentStatus,
+	}
+	// Items
+	for _, it := range state.Items {
+		if it == nil {
+			continue
+		}
+		outlet := toPtr(it.Outlet)
+		storeId := toPtr(it.StoreId)
+		grain.Items = append(grain.Items, &CartItem{
+			Id:          int(it.Id),
+			ItemId:      int(it.ItemId),
+			Sku:         it.Sku,
+			Name:        it.Name,
+			Price:       it.Price,
+			Quantity:    int(it.Qty),
+			TotalPrice:  it.TotalPrice,
+			TotalTax:    it.TotalTax,
+			OrgPrice:    it.OrgPrice,
+			TaxRate:     int(it.TaxRate),
+			Brand:       it.Brand,
+			Category:    it.Category,
+			Category2:   it.Category2,
+			Category3:   it.Category3,
+			Category4:   it.Category4,
+			Category5:   it.Category5,
+			Image:       it.Image,
+			ArticleType: it.Type,
+			SellerId:    it.SellerId,
+			SellerName:  it.SellerName,
+			Disclaimer:  it.Disclaimer,
+			Outlet:      outlet,
+			StoreId:     storeId,
+			Stock:       StockStatus(it.Stock),
+		})
+	}
+	// Deliveries
+	for _, d := range state.Deliveries {
+		if d == nil {
+			continue
+		}
+		intIds := make([]int, 0, len(d.Items))
+		for _, id := range d.Items {
+			intIds = append(intIds, int(id))
+		}
+		grain.Deliveries = append(grain.Deliveries, &CartDelivery{
+			Id:          int(d.Id),
+			Provider:    d.Provider,
+			Price:       d.Price,
+			Items:       intIds,
+			PickupPoint: d.PickupPoint,
+		})
+	}
+
+	return grain, nil
 }
 
-// GetCurrentState calls CartActor.GetState and returns a FrameWithPayload
+// GetCurrentState retrieves the current cart state using the typed StateReply oneof.
-// shaped like the legacy RemoteGetStateReply.
+func (g *RemoteGrainGRPC) GetCurrentState() (*CartGrain, error) {
-func (g *RemoteGrainGRPC) GetCurrentState() (*FrameWithPayload, error) {
 	ctx, cancel := context.WithTimeout(context.Background(), g.stateTimeout)
 	defer cancel()
-
+	resp, err := g.client.GetState(ctx, &proto.StateRequest{CartId: g.Id.String()})
-	resp, err := g.client.GetState(ctx, &proto.StateRequest{
-		CartId: g.Id.String(),
-	})
 	if err != nil {
 		return nil, err
 	}
-	frame := MakeFrameWithPayload(RemoteGetStateReply, StatusCode(resp.StatusCode), resp.Payload)
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
-	return &frame, nil
+		if e := resp.GetError(); e != "" {
+			return nil, fmt.Errorf("remote get state failed %d: %s", resp.StatusCode, e)
+		}
+		return nil, fmt.Errorf("remote get state failed %d", resp.StatusCode)
+	}
+	state := resp.GetState()
+	if state == nil {
+		return nil, fmt.Errorf("state reply missing state on success")
+	}
+	grain := &CartGrain{
+		Id:                ToCartId(state.Id),
+		TotalPrice:        state.TotalPrice,
+		TotalTax:          state.TotalTax,
+		TotalDiscount:     state.TotalDiscount,
+		PaymentInProgress: state.PaymentInProgress,
+		OrderReference:    state.OrderReference,
+		PaymentStatus:     state.PaymentStatus,
+	}
+	for _, it := range state.Items {
+		if it == nil {
+			continue
+		}
+		outlet := toPtr(it.Outlet)
+		storeId := toPtr(it.StoreId)
+		grain.Items = append(grain.Items, &CartItem{
+			Id:          int(it.Id),
+			ItemId:      int(it.ItemId),
+			Sku:         it.Sku,
+			Name:        it.Name,
+			Price:       it.Price,
+			Quantity:    int(it.Qty),
+			TotalPrice:  it.TotalPrice,
+			TotalTax:    it.TotalTax,
+			OrgPrice:    it.OrgPrice,
+			TaxRate:     int(it.TaxRate),
+			Brand:       it.Brand,
+			Category:    it.Category,
+			Category2:   it.Category2,
+			Category3:   it.Category3,
+			Category4:   it.Category4,
+			Category5:   it.Category5,
+			Image:       it.Image,
+			ArticleType: it.Type,
+			SellerId:    it.SellerId,
+			SellerName:  it.SellerName,
+			Disclaimer:  it.Disclaimer,
+			Outlet:      outlet,
+			StoreId:     storeId,
+			Stock:       StockStatus(it.Stock),
+		})
+	}
+	for _, d := range state.Deliveries {
+		if d == nil {
+			continue
+		}
+		intIds := make([]int, 0, len(d.Items))
+		for _, id := range d.Items {
+			intIds = append(intIds, int(id))
+		}
+		grain.Deliveries = append(grain.Deliveries, &CartDelivery{
+			Id:          int(d.Id),
+			Provider:    d.Provider,
+			Price:       d.Price,
+			Items:       intIds,
+			PickupPoint: d.PickupPoint,
+		})
+	}
+
+	return grain, nil
 }
 
 // Close closes the underlying gRPC connection if this adapter created it.

ring.go

@@ -0,0 +1,344 @@
+package main
+
+import (
+	"encoding/binary"
+	"fmt"
+	"hash/fnv"
+	"sort"
+	"strings"
+	"sync"
+)
+
+// ring.go
+//
+// Consistent hashing ring skeleton for future integration.
+// --------------------------------------------------------
+// This file introduces a minimal, allocation‑light consistent hashing structure
+// intended to replace per-cart ownership negotiation. It focuses on:
+//   * Deterministic lookup: O(log V) via binary search
+//   * Even(ish) distribution using virtual nodes (vnodes)
+//   * Epoch / fingerprint tracking to detect membership drift
+//
+// NOT YET WIRED:
+//   * SyncedPool integration (ownerForCart, lazy migration)
+//   * Replication factor > 1
+//   * Persistent state migration
+//
+// Safe to import now; unused until explicit integration code is added.
+//
+// Design Notes
+// ------------
+// - Hosts contribute `vnodesPerHost` virtual nodes. Higher counts smooth
+//   distribution at cost of memory (V = hosts * vnodesPerHost).
+// - Hash of vnode = FNV1a64(host + "#" + index). For improved quality you
+//   can swap in xxhash or siphash later without changing API (but doing so
+//   will reshuffle ownership).
+// - Cart ownership lookup uses either cartID.Raw() when provided (uniform
+//   64-bit space) or falls back to hashing string forms (legacy).
+// - Epoch is monotonically increasing; consumers can fence stale results.
+//
+// Future Extensions
+// -----------------
+// - Weighted hosts (proportionally more vnodes).
+// - Replication: LookupN(h, n) to return primary + replicas.
+// - Streaming / diff-based ring updates (gossip).
+// - Hash function injection for deterministic test scenarios.
+//
+// ---------------------------------------------------------------------------
+
+// Vnode represents a single virtual node position on the ring.
+type Vnode struct {
+	Hash  uint64 // position on the ring
+	Host  string // physical host owning this vnode
+	Index int    // per-host vnode index (0..vnodesPerHost-1)
+}
+
+// Ring is an immutable consistent hash ring snapshot.
+type Ring struct {
+	Epoch       uint64
+	Vnodes      []Vnode // sorted by Hash
+	hosts       []string
+	fingerprint uint64 // membership fingerprint (order-independent)
+}
+
+// RingBuilder accumulates parameters to construct a Ring.
+type RingBuilder struct {
+	epoch         uint64
+	vnodesPerHost int
+	hosts         []string
+}
+
+// NewRingBuilder creates a builder with defaults.
+func NewRingBuilder() *RingBuilder {
+	return &RingBuilder{
+		vnodesPerHost: 64, // a reasonable default for small clusters
+	}
+}
+
+func (b *RingBuilder) WithEpoch(e uint64) *RingBuilder {
+	b.epoch = e
+	return b
+}
+
+func (b *RingBuilder) WithVnodesPerHost(n int) *RingBuilder {
+	if n > 0 {
+		b.vnodesPerHost = n
+	}
+	return b
+}
+
+func (b *RingBuilder) WithHosts(hosts []string) *RingBuilder {
+	uniq := make(map[string]struct{}, len(hosts))
+	out := make([]string, 0, len(hosts))
+	for _, h := range hosts {
+		h = strings.TrimSpace(h)
+		if h == "" {
+			continue
+		}
+		if _, ok := uniq[h]; ok {
+			continue
+		}
+		uniq[h] = struct{}{}
+		out = append(out, h)
+	}
+	sort.Strings(out)
+	b.hosts = out
+	return b
+}
+
+func (b *RingBuilder) Build() *Ring {
+	if len(b.hosts) == 0 {
+		return &Ring{
+			Epoch:       b.epoch,
+			Vnodes:      nil,
+			hosts:       nil,
+			fingerprint: 0,
+		}
+	}
+
+	totalVnodes := len(b.hosts) * b.vnodesPerHost
+	vnodes := make([]Vnode, 0, totalVnodes)
+
+	for _, host := range b.hosts {
+		for i := 0; i < b.vnodesPerHost; i++ {
+			h := hashVnode(host, i)
+			vnodes = append(vnodes, Vnode{
+				Hash:  h,
+				Host:  host,
+				Index: i,
+			})
+		}
+	}
+	sort.Slice(vnodes, func(i, j int) bool {
+		if vnodes[i].Hash == vnodes[j].Hash {
+			// Tie-break deterministically by host then index to avoid instability
+			if vnodes[i].Host == vnodes[j].Host {
+				return vnodes[i].Index < vnodes[j].Index
+			}
+			return vnodes[i].Host < vnodes[j].Host
+		}
+		return vnodes[i].Hash < vnodes[j].Hash
+	})
+
+	fp := fingerprintHosts(b.hosts)
+
+	return &Ring{
+		Epoch:       b.epoch,
+		Vnodes:      vnodes,
+		hosts:       append([]string(nil), b.hosts...),
+		fingerprint: fp,
+	}
+}
+
+// Hosts returns a copy of the host list (sorted).
+func (r *Ring) Hosts() []string {
+	if len(r.hosts) == 0 {
+		return nil
+	}
+	cp := make([]string, len(r.hosts))
+	copy(cp, r.hosts)
+	return cp
+}
+
+// Fingerprint returns a hash representing the unordered membership set.
+func (r *Ring) Fingerprint() uint64 {
+	return r.fingerprint
+}
+
+// Empty indicates ring has no vnodes.
+func (r *Ring) Empty() bool {
+	return len(r.Vnodes) == 0
+}
+
+// Lookup returns the vnode owning a given hash value.
+func (r *Ring) Lookup(h uint64) Vnode {
+	if len(r.Vnodes) == 0 {
+		return Vnode{}
+	}
+	// Binary search: first position with Hash >= h
+	i := sort.Search(len(r.Vnodes), func(i int) bool {
+		return r.Vnodes[i].Hash >= h
+	})
+	if i == len(r.Vnodes) {
+		return r.Vnodes[0]
+	}
+	return r.Vnodes[i]
+}
+
+// LookupID selects owner vnode for a CartID (fast path).
+func (r *Ring) LookupID(id CartID) Vnode {
+	return r.Lookup(id.Raw())
+}
+
+// LookupString hashes an arbitrary string and looks up owner.
+func (r *Ring) LookupString(s string) Vnode {
+	return r.Lookup(hashKeyString(s))
+}
+
+// LookupN returns up to n distinct host vnodes in ring order
+// starting from the primary owner of hash h (for replication).
+func (r *Ring) LookupN(h uint64, n int) []Vnode {
+	if n <= 0 || len(r.Vnodes) == 0 {
+		return nil
+	}
+	if n > len(r.hosts) {
+		n = len(r.hosts)
+	}
+	owners := make([]Vnode, 0, n)
+	seen := make(map[string]struct{}, n)
+
+	start := r.Lookup(h)
+
+	// Find index of start (can binary search again or linear scan; since we
+	// already have start.Hash we do another search for clarity)
+	i := sort.Search(len(r.Vnodes), func(i int) bool {
+		return r.Vnodes[i].Hash >= start.Hash
+	})
+	if i == len(r.Vnodes) {
+		i = 0
+	}
+
+	for idx := 0; len(owners) < n && idx < len(r.Vnodes); idx++ {
+		v := r.Vnodes[(i+idx)%len(r.Vnodes)]
+		if _, ok := seen[v.Host]; ok {
+			continue
+		}
+		seen[v.Host] = struct{}{}
+		owners = append(owners, v)
+	}
+	return owners
+}
+
+// DiffHosts compares this ring's membership to another.
+func (r *Ring) DiffHosts(other *Ring) (added []string, removed []string) {
+	if other == nil {
+		return r.Hosts(), nil
+	}
+	cur := make(map[string]struct{}, len(r.hosts))
+	for _, h := range r.hosts {
+		cur[h] = struct{}{}
+	}
+	oth := make(map[string]struct{}, len(other.hosts))
+	for _, h := range other.hosts {
+		oth[h] = struct{}{}
+	}
+	for h := range cur {
+		if _, ok := oth[h]; !ok {
+			removed = append(removed, h)
+		}
+	}
+	for h := range oth {
+		if _, ok := cur[h]; !ok {
+			added = append(added, h)
+		}
+	}
+	sort.Strings(added)
+	sort.Strings(removed)
+	return
+}
+
+// ---------------------------- Hash Functions ---------------------------------
+
+func hashVnode(host string, idx int) uint64 {
+	h := fnv.New64a()
+	_, _ = h.Write([]byte(host))
+	_, _ = h.Write([]byte{'#'})
+	var buf [8]byte
+	binary.BigEndian.PutUint64(buf[:], uint64(idx))
+	_, _ = h.Write(buf[:])
+	return h.Sum64()
+}
+
+// hashKeyString provides a stable hash for arbitrary string keys (legacy IDs).
+func hashKeyString(s string) uint64 {
+	h := fnv.New64a()
+	_, _ = h.Write([]byte(s))
+	return h.Sum64()
+}
+
+// fingerprintHosts produces an order-insensitive hash over the host set.
+func fingerprintHosts(hosts []string) uint64 {
+	if len(hosts) == 0 {
+		return 0
+	}
+	h := fnv.New64a()
+	for _, host := range hosts {
+		_, _ = h.Write([]byte(host))
+		_, _ = h.Write([]byte{0})
+	}
+	return h.Sum64()
+}
+
+// --------------------------- Thread-Safe Wrapper -----------------------------
+//
+// RingRef offers atomic swap + read semantics. SyncedPool can embed or hold
+// one of these to manage live ring updates safely.
+
+type RingRef struct {
+	mu   sync.RWMutex
+	ring *Ring
+}
+
+func NewRingRef(r *Ring) *RingRef {
+	return &RingRef{ring: r}
+}
+
+func (rr *RingRef) Get() *Ring {
+	rr.mu.RLock()
+	r := rr.ring
+	rr.mu.RUnlock()
+	return r
+}
+
+func (rr *RingRef) Set(r *Ring) {
+	rr.mu.Lock()
+	rr.ring = r
+	rr.mu.Unlock()
+}
+
+func (rr *RingRef) LookupID(id CartID) Vnode {
+	r := rr.Get()
+	if r == nil {
+		return Vnode{}
+	}
+	return r.LookupID(id)
+}
+
+// ----------------------------- Debug Utilities -------------------------------
+
+func (r *Ring) String() string {
+	var b strings.Builder
+	fmt.Fprintf(&b, "Ring{epoch=%d vnodes=%d hosts=%d}\n", r.Epoch, len(r.Vnodes), len(r.hosts))
+	limit := len(r.Vnodes)
+	if limit > 16 {
+		limit = 16
+	}
+	for i := 0; i < limit; i++ {
+		v := r.Vnodes[i]
+		fmt.Fprintf(&b, "  %02d hash=%016x host=%s idx=%d\n", i, v.Hash, v.Host, v.Index)
+	}
+	if len(r.Vnodes) > limit {
+		fmt.Fprintf(&b, "  ... (%d more)\n", len(r.Vnodes)-limit)
+	}
+	return b.String()
+}

synced-pool.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"log"
+	"reflect"
 	"sync"
 	"time"
 
@@ -15,14 +16,15 @@ import (
 )
 
 // SyncedPool coordinates cart grain ownership across nodes using gRPC control plane
-// and cart actor services. Legacy frame / TCP code has been removed.
+// and cart actor services.
 //
 // Responsibilities:
 //   - Local grain access (delegates to GrainLocalPool)
 //   - Remote grain proxy management (RemoteGrainGRPC)
 //   - Cluster membership (AddRemote via discovery + negotiation)
-//   - Ownership acquisition (quorum via ConfirmOwner RPC)
 //   - Health/ping monitoring & remote removal
+//   - Ring based deterministic ownership (no runtime negotiation)
+//   - (Scaffolding) replication factor awareness via ring.LookupN
 //
 // Thread-safety: public methods that mutate internal maps lock p.mu (RWMutex).
 type SyncedPool struct {
@@ -40,7 +42,12 @@ type SyncedPool struct {
 	// Discovery handler for re-adding hosts after failures
 	discardedHostHandler *DiscardedHostHandler
 
-	// Metrics / instrumentation dependencies already declared globally
+	// Consistent hashing ring (immutable snapshot reference)
+	ringRef *RingRef
+
+	// Configuration
+	vnodesPerHost     int
+	replicationFactor int // RF (>=1). Currently only primary is active; replicas are scaffolding.
 }
 
 // RemoteHostGRPC tracks a remote host's clients & health.
@@ -71,7 +78,54 @@ var (
 	})
 	remoteLookupCount = promauto.NewCounter(prometheus.CounterOpts{
 		Name: "cart_remote_lookup_total",
-		Help: "The total number of remote lookups",
+		Help: "The total number of remote lookups (legacy counter)",
+	})
+
+	// Ring / ownership metrics
+	ringEpoch = promauto.NewGauge(prometheus.GaugeOpts{
+		Name: "cart_ring_epoch",
+		Help: "Current consistent hashing ring epoch (fingerprint-based pseudo-epoch)",
+	})
+	ringHosts = promauto.NewGauge(prometheus.GaugeOpts{
+		Name: "cart_ring_hosts",
+		Help: "Number of hosts currently in the ring",
+	})
+	ringVnodes = promauto.NewGauge(prometheus.GaugeOpts{
+		Name: "cart_ring_vnodes",
+		Help: "Number of virtual nodes in the ring",
+	})
+	ringLookupLocal = promauto.NewCounter(prometheus.CounterOpts{
+		Name: "cart_ring_lookup_local_total",
+		Help: "Ring ownership lookups resolved to the local host",
+	})
+	ringLookupRemote = promauto.NewCounter(prometheus.CounterOpts{
+		Name: "cart_ring_lookup_remote_total",
+		Help: "Ring ownership lookups resolved to a remote host",
+	})
+	ringHostShare = promauto.NewGaugeVec(prometheus.GaugeOpts{
+		Name: "cart_ring_host_share",
+		Help: "Fractional share of ring vnodes per host",
+	}, []string{"host"})
+
+	cartMutationsTotal = promauto.NewCounter(prometheus.CounterOpts{
+		Name: "cart_mutations_total",
+		Help: "Total number of cart state mutations applied (local + remote routed).",
+	})
+
+	cartMutationFailuresTotal = promauto.NewCounter(prometheus.CounterOpts{
+		Name: "cart_mutation_failures_total",
+		Help: "Total number of failed cart state mutations (local apply errors or remote routing failures).",
+	})
+
+	cartMutationLatencySeconds = promauto.NewHistogramVec(prometheus.HistogramOpts{
+		Name:    "cart_mutation_latency_seconds",
+		Help:    "Latency of cart mutations (successful or failed) in seconds.",
+		Buckets: prometheus.DefBuckets,
+	}, []string{"mutation"})
+
+	cartActiveGrains = promauto.NewGauge(prometheus.GaugeOpts{
+		Name: "cart_active_grains",
+		Help: "Number of active (resident) local grains.",
 	})
 )
 
@@ -82,8 +136,12 @@ func NewSyncedPool(local *GrainLocalPool, hostname string, discovery Discovery)
 		remoteHosts:          make(map[string]*RemoteHostGRPC),
 		remoteIndex:          make(map[CartId]Grain),
 		discardedHostHandler: NewDiscardedHostHandler(1338),
+		vnodesPerHost:        64, // default smoothing factor; adjust if needed
+		replicationFactor:    1,  // RF scaffold; >1 not yet activating replicas
 	}
 	p.discardedHostHandler.SetReconnectHandler(p.AddRemote)
+	// Initialize empty ring (will be rebuilt after first AddRemote or discovery event)
+	p.rebuildRing()
 
 	if discovery != nil {
 		go func() {
@@ -175,6 +233,8 @@ func (p *SyncedPool) AddRemote(host string) {
 	p.remoteHosts[host] = remote
 	p.mu.Unlock()
 	connectedRemotes.Set(float64(p.RemoteCount()))
+	// Rebuild consistent hashing ring including this new host
+	p.rebuildRing()
 
 	log.Printf("Connected to remote host %s", host)
 
@@ -222,6 +282,8 @@ func (p *SyncedPool) RemoveHost(host string) {
 		remote.Conn.Close()
 	}
 	connectedRemotes.Set(float64(p.RemoteCount()))
+	// Rebuild ring after host removal
+	p.rebuildRing()
 }
 
 // RemoteCount returns number of tracked remote hosts.
@@ -302,6 +364,8 @@ func (p *SyncedPool) Negotiate() {
 	}
 	p.mu.RUnlock()
 
+	changed := false
+
 	for _, r := range remotes {
 		ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
 		reply, err := r.ControlClient.Negotiate(ctx, &proto.NegotiateRequest{KnownHosts: hosts})
@@ -313,12 +377,18 @@ func (p *SyncedPool) Negotiate() {
 		for _, h := range reply.Hosts {
 			if !p.IsKnown(h) {
 				p.AddRemote(h)
+				changed = true
 			}
 		}
 	}
+
+	// If new hosts were discovered during negotiation, rebuild the ring once at the end.
+	if changed {
+		p.rebuildRing()
+	}
 }
 
-// ------------------------- Grain Management ----------------------------------
+// ------------------------- Grain / Ring Ownership ----------------------------
 
 // RemoveRemoteGrain removes a remote grain mapping.
 func (p *SyncedPool) RemoveRemoteGrain(id CartId) {
@@ -333,9 +403,9 @@ func (p *SyncedPool) SpawnRemoteGrain(id CartId, host string) {
 		return
 	}
 	p.mu.Lock()
-	// If local grain exists, remove it (ownership changed)
+	// If local grain exists (legacy key), remove from local map (ownership moved).
-	if g, ok := p.local.grains[id]; ok && g != nil {
+	if g, ok := p.local.grains[LegacyToCartKey(id)]; ok && g != nil {
-		delete(p.local.grains, id)
+		delete(p.local.grains, LegacyToCartKey(id))
 	}
 	remoteHost, ok := p.remoteHosts[host]
 	if !ok {
@@ -362,88 +432,192 @@ func (p *SyncedPool) GetHealthyRemotes() []*RemoteHostGRPC {
 	return ret
 }
 
-// RequestOwnership attempts to become owner of a cart, requiring quorum.
+// rebuildRing reconstructs the consistent hashing ring from current host set
-// On success local grain is (or will be) created; peers spawn remote proxies.
+// and updates ring-related metrics.
-func (p *SyncedPool) RequestOwnership(id CartId) error {
+func (p *SyncedPool) rebuildRing() {
-	ok := 0
+	p.mu.RLock()
-	all := 0
+	hosts := make([]string, 0, len(p.remoteHosts)+1)
-	remotes := p.GetHealthyRemotes()
+	hosts = append(hosts, p.Hostname)
-	for _, r := range remotes {
+	for h := range p.remoteHosts {
-		ctx, cancel := context.WithTimeout(context.Background(), 800*time.Millisecond)
+		hosts = append(hosts, h)
-		reply, err := r.ControlClient.ConfirmOwner(ctx, &proto.OwnerChangeRequest{
+	}
-			CartId:  id.String(),
+	p.mu.RUnlock()
-			NewHost: p.Hostname,
+
-		})
+	epochSeed := fingerprintHosts(hosts)
-		cancel()
+	builder := NewRingBuilder().
-		all++
+		WithHosts(hosts).
-		if err != nil || reply == nil || !reply.Accepted {
+		WithEpoch(epochSeed).
-			log.Printf("ConfirmOwner failure from %s for %s: %v (reply=%v)", r.Host, id, err, reply)
+		WithVnodesPerHost(p.vnodesPerHost)
-			continue
+	r := builder.Build()
-		}
+	if p.ringRef == nil {
-		ok++
+		p.ringRef = NewRingRef(r)
+	} else {
+		p.ringRef.Set(r)
 	}
 
-	// Quorum rule mirrors legacy:
+	// Metrics
-	//  - If fewer than 3 total, require all.
+	ringEpoch.Set(float64(r.Epoch))
-	//  - Else require majority (ok >= all/2).
+	ringHosts.Set(float64(len(r.Hosts())))
-	if (all < 3 && ok < all) || ok < (all/2) {
+	ringVnodes.Set(float64(len(r.Vnodes)))
-		p.removeLocalGrain(id)
+	ringHostShare.Reset()
-		return fmt.Errorf("quorum not reached (ok=%d all=%d)", ok, all)
+	if len(r.Vnodes) > 0 {
+		perHost := make(map[string]int)
+		for _, v := range r.Vnodes {
+			perHost[v.Host]++
+		}
+		total := float64(len(r.Vnodes))
+		for h, c := range perHost {
+			ringHostShare.WithLabelValues(h).Set(float64(c) / total)
+		}
 	}
-	grainSyncCount.Inc()
+}
-	return nil
+
+// ForceRingRefresh exposes a manual ring rebuild hook (primarily for tests).
+func (p *SyncedPool) ForceRingRefresh() {
+	p.rebuildRing()
+}
+
+// ownersFor returns the ordered list of primary + replica owners for a cart id
+// (length min(replicationFactor, #hosts)). Currently only the first (primary)
+// is used. This scaffolds future replication work.
+func (p *SyncedPool) ownersFor(id CartId) []string {
+	if p.ringRef == nil || p.replicationFactor <= 0 {
+		return []string{p.Hostname}
+	}
+	r := p.ringRef.Get()
+	if r == nil || r.Empty() {
+		return []string{p.Hostname}
+	}
+	vnodes := r.LookupN(hashKeyString(id.String()), p.replicationFactor)
+	out := make([]string, 0, len(vnodes))
+	seen := make(map[string]struct{}, len(vnodes))
+	for _, v := range vnodes {
+		if _, ok := seen[v.Host]; ok {
+			continue
+		}
+		seen[v.Host] = struct{}{}
+		out = append(out, v.Host)
+	}
+	if len(out) == 0 {
+		out = append(out, p.Hostname)
+	}
+	return out
+}
+
+// ownerHostFor returns the primary owner host for a given id.
+func (p *SyncedPool) ownerHostFor(id CartId) string {
+	return p.ownersFor(id)[0]
+}
+
+// DebugOwnerHost exposes (for tests) the currently computed primary owner host.
+func (p *SyncedPool) DebugOwnerHost(id CartId) string {
+	return p.ownerHostFor(id)
 }
 
 func (p *SyncedPool) removeLocalGrain(id CartId) {
 	p.mu.Lock()
-	delete(p.local.grains, id)
+	delete(p.local.grains, LegacyToCartKey(id))
 	p.mu.Unlock()
 }
 
-// getGrain returns a local or remote grain; if absent, attempts ownership.
+// getGrain returns a local or remote grain. For remote ownership it performs a
+// bounded readiness wait (small retries) to reduce first-call failures while
+// the remote connection & proxy are initializing.
 func (p *SyncedPool) getGrain(id CartId) (Grain, error) {
+	owner := p.ownerHostFor(id)
+	if owner == p.Hostname {
+		ringLookupLocal.Inc()
+		grain, err := p.local.GetGrain(id)
+		if err != nil {
+			return nil, err
+		}
+		return grain, nil
+	}
+	ringLookupRemote.Inc()
+
+	// Kick off remote dial if we don't yet know the owner.
+	if !p.IsKnown(owner) {
+		go p.AddRemote(owner)
+	}
+
+	// Fast path existing proxy
 	p.mu.RLock()
-	localGrain, isLocal := p.local.grains[id]
+	if rg, ok := p.remoteIndex[id]; ok {
-	remoteGrain, isRemote := p.remoteIndex[id]
+		p.mu.RUnlock()
+		remoteLookupCount.Inc()
+		return rg, nil
+	}
 	p.mu.RUnlock()
 
-	if isLocal && localGrain != nil {
+	const (
-		return localGrain, nil
+		attempts    = 5
-	}
+		sleepPerTry = 40 * time.Millisecond
-	if isRemote {
+	)
-		remoteLookupCount.Inc()
+
-		return remoteGrain, nil
+	for attempt := 0; attempt < attempts; attempt++ {
+		// Try to spawn (idempotent if host already known)
+		if p.IsKnown(owner) {
+			p.SpawnRemoteGrain(id, owner)
+		}
+		// Check again
+		p.mu.RLock()
+		if rg, ok := p.remoteIndex[id]; ok {
+			p.mu.RUnlock()
+			remoteLookupCount.Inc()
+			return rg, nil
+		}
+		p.mu.RUnlock()
+
+		// Last attempt? break to return error.
+		if attempt == attempts-1 {
+			break
+		}
+		time.Sleep(sleepPerTry)
 	}
 
-	// Attempt to claim ownership (async semantics preserved)
+	return nil, fmt.Errorf("remote owner %s not yet available for cart %s (after %d attempts)", owner, id.String(), attempts)
-	go p.RequestOwnership(id)
-
-	// Create local grain (lazy spawn) - may be rolled back by quorum failure
-	grain, err := p.local.GetGrain(id)
-	if err != nil {
-		return nil, err
-	}
-	return grain, nil
 }
 
-// Process applies mutation(s) to a grain (local or remote).
+// Apply applies a single mutation to a grain (local or remote).
-func (p *SyncedPool) Process(id CartId, messages ...Message) (*FrameWithPayload, error) {
+// Replication (RF>1) scaffolding: future enhancement will fan-out mutations
+// to replica owners (best-effort) and reconcile quorum on read.
+func (p *SyncedPool) Apply(id CartId, mutation interface{}) (*CartGrain, error) {
 	grain, err := p.getGrain(id)
 	if err != nil {
 		return nil, err
 	}
-	var res *FrameWithPayload
+	start := time.Now()
-	for _, m := range messages {
+	result, applyErr := grain.Apply(mutation, false)
-		res, err = grain.HandleMessage(&m, false)
+
-		if err != nil {
+	// Derive mutation type label (strip pointer)
-			return nil, err
+	mutationType := "unknown"
+	if mutation != nil {
+		if t := reflect.TypeOf(mutation); t != nil {
+			if t.Kind() == reflect.Ptr {
+				t = t.Elem()
+			}
+			if t.Name() != "" {
+				mutationType = t.Name()
+			}
 		}
 	}
-	return res, nil
+	cartMutationLatencySeconds.WithLabelValues(mutationType).Observe(time.Since(start).Seconds())
+
+	if applyErr == nil && result != nil {
+		cartMutationsTotal.Inc()
+		if p.ownerHostFor(id) == p.Hostname {
+			// Update active grains gauge only for local ownership
+			cartActiveGrains.Set(float64(p.local.DebugGrainCount()))
+		}
+	} else if applyErr != nil {
+		cartMutationFailuresTotal.Inc()
+	}
+	return result, applyErr
 }
 
 // Get returns current state of a grain (local or remote).
-func (p *SyncedPool) Get(id CartId) (*FrameWithPayload, error) {
+// Future replication hook: Read-repair or quorum read can be added here.
+func (p *SyncedPool) Get(id CartId) (*CartGrain, error) {
 	grain, err := p.getGrain(id)
 	if err != nil {
 		return nil, err