all the refactor

2026-06-28 17:51:52 +02:00
parent 7db0d236c7
commit aa8b2bdedc
84 changed files with 4328 additions and 2344 deletions
@@ -5,6 +5,7 @@ import (
 	"fmt"

 	"git.k6n.net/mats/go-cart-actor/pkg/promotions"
+	pmcp "git.k6n.net/mats/platform/mcp"
 )

 // AdminTool is one admin promotion tool definition — name, description, input
@@ -31,14 +32,14 @@ func AdminTools(store *promotions.Store, eval *promotions.PromotionService) []Ad
 				"`promotion` is a full promotion-rule object (id, name, status, priority, conditions, actions). " +
 				"For a tiered volume discount (Volymrabatt) use a cart_total condition plus a tiered_discount action " +
 				"whose config.tiers each have minTotal/maxTotal (öre incl. VAT) and percent.",
-			InputSchema: object(props{
-				"promotion": obj("the full promotion rule object"),
+			InputSchema: pmcp.Object(pmcp.Props{
+				"promotion": pmcp.ObjectValue("the full promotion rule object"),
 			}, []string{"promotion"}),
 			Invoke: func(args json.RawMessage) (any, error) {
 				var a struct {
 					Promotion json.RawMessage `json:"promotion"`
 				}
-				if err := decode(args, &a); err != nil {
+				if err := pmcp.Decode(args, &a); err != nil {
 					return nil, err
 				}
 				var rule promotions.PromotionRule
@@ -61,16 +62,16 @@ func AdminTools(store *promotions.Store, eval *promotions.PromotionService) []Ad
 		{
 			Name:        "set_promotion_status",
 			Description: "Set a promotion's status (active|inactive|scheduled|expired) to toggle it on or off.",
-			InputSchema: object(props{
-				"id":     str("the promotion id"),
-				"status": str("new status: active|inactive|scheduled|expired"),
+			InputSchema: pmcp.Object(pmcp.Props{
+				"id":     pmcp.String("the promotion id"),
+				"status": pmcp.String("new status: active|inactive|scheduled|expired"),
 			}, []string{"id", "status"}),
 			Invoke: func(args json.RawMessage) (any, error) {
 				var a struct {
 					ID     string `json:"id"`
 					Status string `json:"status"`
 				}
-				if err := decode(args, &a); err != nil {
+				if err := pmcp.Decode(args, &a); err != nil {
 					return nil, err
 				}
 				if !validStatus(a.Status) {
@@ -89,12 +90,12 @@ func AdminTools(store *promotions.Store, eval *promotions.PromotionService) []Ad
 		{
 			Name:        "delete_promotion",
 			Description: "Delete a promotion rule by id.",
-			InputSchema: object(props{"id": str("the promotion id")}, []string{"id"}),
+			InputSchema: pmcp.Object(pmcp.Props{"id": pmcp.String("the promotion id")}, []string{"id"}),
 			Invoke: func(args json.RawMessage) (any, error) {
 				var a struct {
 					ID string `json:"id"`
 				}
-				if err := decode(args, &a); err != nil {
+				if err := pmcp.Decode(args, &a); err != nil {
 					return nil, err
 				}
 				found, err := store.Delete(a.ID)
@@ -1,44 +0,0 @@
-package mcp
-
-import "encoding/json"
-
-// JSON-RPC 2.0 envelope types (the wire format MCP rides on). Notifications are
-// requests with no id and must not receive a response.
-
-type rpcRequest struct {
-	JSONRPC string          `json:"jsonrpc"`
-	ID      json.RawMessage `json:"id,omitempty"`
-	Method  string          `json:"method"`
-	Params  json.RawMessage `json:"params,omitempty"`
-}
-
-func (r *rpcRequest) isNotification() bool { return len(r.ID) == 0 }
-
-type rpcResponse struct {
-	JSONRPC string          `json:"jsonrpc"`
-	ID      json.RawMessage `json:"id,omitempty"`
-	Result  any             `json:"result,omitempty"`
-	Error   *rpcError       `json:"error,omitempty"`
-}
-
-type rpcError struct {
-	Code    int    `json:"code"`
-	Message string `json:"message"`
-	Data    any    `json:"data,omitempty"`
-}
-
-const (
-	codeParseError     = -32700
-	codeInvalidRequest = -32600
-	codeMethodNotFound = -32601
-	codeInvalidParams  = -32602
-	codeInternalError  = -32603
-)
-
-func result(id json.RawMessage, v any) *rpcResponse {
-	return &rpcResponse{JSONRPC: "2.0", ID: id, Result: v}
-}
-
-func errorResponse(id json.RawMessage, code int, msg string) *rpcResponse {
-	return &rpcResponse{JSONRPC: "2.0", ID: id, Error: &rpcError{Code: code, Message: msg}}
-}
@@ -4,160 +4,39 @@
 // cart actually applies (e.g. Volymrabatt), plus preview the discount a cart
 // total would receive.
 //
-// Transport is streamable HTTP (JSON-RPC 2.0 over POST). It is mounted by
-// cmd/cart under /mcp on the same HTTP server as the cart API. Tools mutate the
-// shared promotions.Store and persist to data/promotions.json; the cart's
-// mutation processor reads a fresh Store snapshot on every recompute, so edits
-// take effect on the next cart change without a restart.
+// Transport/dispatch and the schema/result helpers live in platform/mcp; this
+// package defines the promotion tools (full set via New, read-only via NewPublic)
+// and the admin tools (AdminTools) that backoffice merges into the CMS MCP.
 package mcp

 import (
-	"encoding/json"
-	"io"
 	"net/http"

 	"git.k6n.net/mats/go-cart-actor/pkg/promotions"
+	pmcp "git.k6n.net/mats/platform/mcp"
 )

 const (
-	serverName      = "cart-promotions"
-	serverVersion   = "0.1.0"
-	protocolVersion = "2025-06-18"
+	serverName    = "cart-promotions"
+	serverVersion = "0.1.0"
 )

 // Server is the MCP edge over the shared promotion Store and evaluator.
 type Server struct {
 	store *promotions.Store
 	eval  *promotions.PromotionService
-	tools []tool
+	mcp   *pmcp.Server
 }

-// New builds an MCP server exposing the promotion store as tools.
+// New builds an MCP server exposing the full promotion tool set.
 func New(store *promotions.Store, eval *promotions.PromotionService) *Server {
 	if eval == nil {
 		eval = promotions.NewPromotionService(nil)
 	}
 	s := &Server{store: store, eval: eval}
-	s.tools = s.buildTools()
+	s.mcp = pmcp.NewServer(pmcp.Info{Name: serverName, Version: serverVersion}, s.buildTools()...)
 	return s
 }

 // Handler returns the streamable-HTTP handler to mount (e.g. at /mcp).
-func (s *Server) Handler() http.Handler {
-	return http.HandlerFunc(s.serveHTTP)
-}
-
-func (s *Server) serveHTTP(w http.ResponseWriter, r *http.Request) {
-	if r.Method != http.MethodPost {
-		w.Header().Set("Allow", "POST")
-		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
-		return
-	}
-	body, err := io.ReadAll(io.LimitReader(r.Body, 4<<20))
-	if err != nil {
-		writeRPC(w, errorResponse(nil, codeParseError, "read error"))
-		return
-	}
-	if isBatch(body) {
-		var reqs []rpcRequest
-		if err := json.Unmarshal(body, &reqs); err != nil {
-			writeRPC(w, errorResponse(nil, codeParseError, "invalid JSON"))
-			return
-		}
-		var out []*rpcResponse
-		for i := range reqs {
-			if resp := s.dispatch(&reqs[i]); resp != nil {
-				out = append(out, resp)
-			}
-		}
-		if len(out) == 0 {
-			w.WriteHeader(http.StatusAccepted)
-			return
-		}
-		writeRPC(w, out)
-		return
-	}
-	var req rpcRequest
-	if err := json.Unmarshal(body, &req); err != nil {
-		writeRPC(w, errorResponse(nil, codeParseError, "invalid JSON"))
-		return
-	}
-	resp := s.dispatch(&req)
-	if resp == nil {
-		w.WriteHeader(http.StatusAccepted)
-		return
-	}
-	writeRPC(w, resp)
-}
-
-func (s *Server) dispatch(req *rpcRequest) *rpcResponse {
-	if req.JSONRPC != "2.0" {
-		if req.isNotification() {
-			return nil
-		}
-		return errorResponse(req.ID, codeInvalidRequest, "jsonrpc must be \"2.0\"")
-	}
-	switch req.Method {
-	case "initialize":
-		return result(req.ID, s.initialize(req.Params))
-	case "ping":
-		return result(req.ID, struct{}{})
-	case "tools/list":
-		return result(req.ID, map[string]any{"tools": s.tools})
-	case "tools/call":
-		return s.callTool(req)
-	case "notifications/initialized", "notifications/cancelled":
-		return nil
-	default:
-		if req.isNotification() {
-			return nil
-		}
-		return errorResponse(req.ID, codeMethodNotFound, "unknown method: "+req.Method)
-	}
-}
-
-func (s *Server) initialize(params json.RawMessage) map[string]any {
-	pv := protocolVersion
-	if len(params) > 0 {
-		var p struct {
-			ProtocolVersion string `json:"protocolVersion"`
-		}
-		if json.Unmarshal(params, &p) == nil && p.ProtocolVersion != "" {
-			pv = p.ProtocolVersion
-		}
-	}
-	return map[string]any{
-		"protocolVersion": pv,
-		"capabilities":    map[string]any{"tools": map[string]any{}},
-		"serverInfo":      map[string]any{"name": serverName, "version": serverVersion},
-	}
-}
-
-// defaultVatRate returns the default VAT rate from the eval service's
-// configured tax provider, falling back to 25 if none is set.
-func (s *Server) defaultVatRate() float32 {
-	if s.eval == nil || s.eval.DefaultTaxProvider == nil {
-		return 25
-	}
-	return float32(s.eval.DefaultTaxProvider.DefaultTaxRate(""))
-}
-
-func isBatch(body []byte) bool {
-	for _, b := range body {
-		switch b {
-		case ' ', '\t', '\r', '\n':
-			continue
-		case '[':
-			return true
-		default:
-			return false
-		}
-	}
-	return false
-}
-
-func writeRPC(w http.ResponseWriter, v any) {
-	w.Header().Set("Content-Type", "application/json")
-	w.WriteHeader(http.StatusOK)
-	_ = json.NewEncoder(w).Encode(v)
-}
+func (s *Server) Handler() http.Handler { return s.mcp.Handler() }
@@ -1,11 +1,13 @@
 package mcp

 import (
+	"context"
 	"encoding/json"
 	"fmt"
 	"time"

 	"git.k6n.net/mats/go-cart-actor/pkg/promotions"
+	pmcp "git.k6n.net/mats/platform/mcp"
 )

 // NewPublic builds an MCP server exposing only the read-only promotion tools:
@@ -17,23 +19,23 @@ func NewPublic(store *promotions.Store, eval *promotions.PromotionService) *Serv
 		eval = promotions.NewPromotionService(nil)
 	}
 	s := &Server{store: store, eval: eval}
-	s.tools = s.buildPublicTools()
+	s.mcp = pmcp.NewServer(pmcp.Info{Name: serverName, Version: serverVersion}, s.buildPublicTools()...)
 	return s
 }

-func (s *Server) buildPublicTools() []tool {
-	return []tool{
+func (s *Server) buildPublicTools() []pmcp.Tool {
+	return []pmcp.Tool{
 		{
 			Name:        "list_promotions",
 			Description: "List all promotion rules the cart engine evaluates, optionally filtered by status (active|inactive|scheduled|expired).",
-			InputSchema: object(props{
-				"status": str("optional status filter: active|inactive|scheduled|expired"),
+			InputSchema: pmcp.Object(pmcp.Props{
+				"status": pmcp.String("optional status filter: active|inactive|scheduled|expired"),
 			}, nil),
-			invoke: func(args json.RawMessage) (any, error) {
+			Invoke: func(_ context.Context, args json.RawMessage) (any, error) {
 				var a struct {
 					Status string `json:"status"`
 				}
-				if err := decode(args, &a); err != nil {
+				if err := pmcp.Decode(args, &a); err != nil {
 					return nil, err
 				}
 				rules := s.store.List()
@@ -52,12 +54,12 @@ func (s *Server) buildPublicTools() []tool {
 		{
 			Name:        "get_promotion",
 			Description: "Fetch a single promotion rule by id.",
-			InputSchema: object(props{"id": str("the promotion id")}, []string{"id"}),
-			invoke: func(args json.RawMessage) (any, error) {
+			InputSchema: pmcp.Object(pmcp.Props{"id": pmcp.String("the promotion id")}, []string{"id"}),
+			Invoke: func(_ context.Context, args json.RawMessage) (any, error) {
 				var a struct {
 					ID string `json:"id"`
 				}
-				if err := decode(args, &a); err != nil {
+				if err := pmcp.Decode(args, &a); err != nil {
 					return nil, err
 				}
 				r, ok := s.store.Get(a.ID)
@@ -72,18 +74,18 @@ func (s *Server) buildPublicTools() []tool {
 			Description: "Evaluate the current active promotions against a hypothetical cart total and report the " +
 				"matched discount. cartTotalIncVat is in öre incl. VAT (e.g. 5 000 000 = 50 000 kr). Useful for " +
 				"verifying Volymrabatt tiers without touching a real cart.",
-			InputSchema: object(props{
-				"cartTotalIncVat": integer("cart total incl. VAT, in öre"),
-				"itemQuantity":    integer("optional total item quantity"),
-				"customerSegment": str("optional customer segment"),
+			InputSchema: pmcp.Object(pmcp.Props{
+				"cartTotalIncVat": pmcp.Integer("cart total incl. VAT, in öre"),
+				"itemQuantity":    pmcp.Integer("optional total item quantity"),
+				"customerSegment": pmcp.String("optional customer segment"),
 			}, []string{"cartTotalIncVat"}),
-			invoke: func(args json.RawMessage) (any, error) {
+			Invoke: func(_ context.Context, args json.RawMessage) (any, error) {
 				var a struct {
 					CartTotalIncVat int64  `json:"cartTotalIncVat"`
 					ItemQuantity    int    `json:"itemQuantity"`
 					CustomerSegment string `json:"customerSegment"`
 				}
-				if err := decode(args, &a); err != nil {
+				if err := pmcp.Decode(args, &a); err != nil {
 					return nil, err
 				}
 				g := syntheticCart(a.CartTotalIncVat, a.ItemQuantity, s.defaultVatRate())
@@ -109,20 +111,20 @@ func (s *Server) buildPublicTools() []tool {
 				"which promotions match, what discount they apply, and any pending next-tier nudges (\"spend X more for Y%\"). " +
 				"When promotionId is set, only that specific promotion is evaluated (useful for testing a new rule). " +
 				"When omitted, all active promotions are evaluated. cartTotalIncVat is in öre incl. VAT.",
-			InputSchema: object(props{
-				"cartTotalIncVat": integer("cart total incl. VAT, in öre"),
-				"promotionId":     str("optional: evaluate only this promotion (by id)"),
-				"itemQuantity":    integer("optional total item quantity"),
-				"customerSegment": str("optional customer segment"),
+			InputSchema: pmcp.Object(pmcp.Props{
+				"cartTotalIncVat": pmcp.Integer("cart total incl. VAT, in öre"),
+				"promotionId":     pmcp.String("optional: evaluate only this promotion (by id)"),
+				"itemQuantity":    pmcp.Integer("optional total item quantity"),
+				"customerSegment": pmcp.String("optional customer segment"),
 			}, []string{"cartTotalIncVat"}),
-			invoke: func(args json.RawMessage) (any, error) {
+			Invoke: func(_ context.Context, args json.RawMessage) (any, error) {
 				var a struct {
 					CartTotalIncVat int64  `json:"cartTotalIncVat"`
 					PromotionId     string `json:"promotionId"`
 					ItemQuantity    int    `json:"itemQuantity"`
 					CustomerSegment string `json:"customerSegment"`
 				}
-				if err := decode(args, &a); err != nil {
+				if err := pmcp.Decode(args, &a); err != nil {
 					return nil, err
 				}

@@ -151,10 +153,10 @@ func (s *Server) buildPublicTools() []tool {
 				evalResults := make([]map[string]any, 0, len(results))
 				for _, r := range results {
 					evalResults = append(evalResults, map[string]any{
-						"ruleId":       r.Rule.ID,
-						"name":         r.Rule.Name,
-						"applicable":   r.Applicable,
-						"failedReason": r.FailedReason,
+						"ruleId":         r.Rule.ID,
+						"name":           r.Rule.Name,
+						"applicable":     r.Applicable,
+						"failedReason":   r.FailedReason,
 						"matchedActions": r.MatchedActions,
 					})
 				}
@@ -1,61 +1,32 @@
 package mcp

 import (
+	"context"
 	"encoding/json"
 	"fmt"
 	"time"

 	"git.k6n.net/mats/go-cart-actor/pkg/cart"
 	"git.k6n.net/mats/go-cart-actor/pkg/promotions"
+	pmcp "git.k6n.net/mats/platform/mcp"
+	"git.k6n.net/mats/platform/tax"
 )

 // tool is one MCP tool: a name, a description, a JSON-Schema for its arguments,
 // and the handler that runs it.
-type tool struct {
-	Name        string                                  `json:"name"`
-	Description string                                  `json:"description"`
-	InputSchema json.RawMessage                         `json:"inputSchema"`
-	invoke      func(args json.RawMessage) (any, error) `json:"-"`
-}
-
-func (s *Server) callTool(req *rpcRequest) *rpcResponse {
-	var p struct {
-		Name      string          `json:"name"`
-		Arguments json.RawMessage `json:"arguments"`
-	}
-	if err := json.Unmarshal(req.Params, &p); err != nil {
-		return errorResponse(req.ID, codeInvalidParams, "invalid params")
-	}
-	var t *tool
-	for i := range s.tools {
-		if s.tools[i].Name == p.Name {
-			t = &s.tools[i]
-			break
-		}
-	}
-	if t == nil {
-		return errorResponse(req.ID, codeInvalidParams, "unknown tool: "+p.Name)
-	}
-	out, err := t.invoke(p.Arguments)
-	if err != nil {
-		return result(req.ID, toolError(err))
-	}
-	return result(req.ID, toolText(out))
-}
-
-func (s *Server) buildTools() []tool {
-	return []tool{
+func (s *Server) buildTools() []pmcp.Tool {
+	return []pmcp.Tool{
 		{
 			Name:        "list_promotions",
 			Description: "List all promotion rules the cart engine evaluates, optionally filtered by status (active|inactive|scheduled|expired).",
-			InputSchema: object(props{
-				"status": str("optional status filter: active|inactive|scheduled|expired"),
+			InputSchema: pmcp.Object(pmcp.Props{
+				"status": pmcp.String("optional status filter: active|inactive|scheduled|expired"),
 			}, nil),
-			invoke: func(args json.RawMessage) (any, error) {
+			Invoke: func(_ context.Context, args json.RawMessage) (any, error) {
 				var a struct {
 					Status string `json:"status"`
 				}
-				if err := decode(args, &a); err != nil {
+				if err := pmcp.Decode(args, &a); err != nil {
 					return nil, err
 				}
 				rules := s.store.List()
@@ -74,12 +45,12 @@ func (s *Server) buildTools() []tool {
 		{
 			Name:        "get_promotion",
 			Description: "Fetch a single promotion rule by id.",
-			InputSchema: object(props{"id": str("the promotion id")}, []string{"id"}),
-			invoke: func(args json.RawMessage) (any, error) {
+			InputSchema: pmcp.Object(pmcp.Props{"id": pmcp.String("the promotion id")}, []string{"id"}),
+			Invoke: func(_ context.Context, args json.RawMessage) (any, error) {
 				var a struct {
 					ID string `json:"id"`
 				}
-				if err := decode(args, &a); err != nil {
+				if err := pmcp.Decode(args, &a); err != nil {
 					return nil, err
 				}
 				r, ok := s.store.Get(a.ID)
@@ -95,14 +66,14 @@ func (s *Server) buildTools() []tool {
 				"`promotion` is a full promotion-rule object (id, name, status, priority, conditions, actions). " +
 				"For a tiered volume discount (Volymrabatt) use a cart_total condition plus a tiered_discount action " +
 				"whose config.tiers each have minTotal/maxTotal (öre incl. VAT) and percent.",
-			InputSchema: object(props{
-				"promotion": obj("the full promotion rule object"),
+			InputSchema: pmcp.Object(pmcp.Props{
+				"promotion": pmcp.ObjectValue("the full promotion rule object"),
 			}, []string{"promotion"}),
-			invoke: func(args json.RawMessage) (any, error) {
+			Invoke: func(_ context.Context, args json.RawMessage) (any, error) {
 				var a struct {
 					Promotion json.RawMessage `json:"promotion"`
 				}
-				if err := decode(args, &a); err != nil {
+				if err := pmcp.Decode(args, &a); err != nil {
 					return nil, err
 				}
 				var rule promotions.PromotionRule
@@ -125,16 +96,16 @@ func (s *Server) buildTools() []tool {
 		{
 			Name:        "set_promotion_status",
 			Description: "Set a promotion's status (active|inactive|scheduled|expired) to toggle it on or off.",
-			InputSchema: object(props{
-				"id":     str("the promotion id"),
-				"status": str("new status: active|inactive|scheduled|expired"),
+			InputSchema: pmcp.Object(pmcp.Props{
+				"id":     pmcp.String("the promotion id"),
+				"status": pmcp.String("new status: active|inactive|scheduled|expired"),
 			}, []string{"id", "status"}),
-			invoke: func(args json.RawMessage) (any, error) {
+			Invoke: func(_ context.Context, args json.RawMessage) (any, error) {
 				var a struct {
 					ID     string `json:"id"`
 					Status string `json:"status"`
 				}
-				if err := decode(args, &a); err != nil {
+				if err := pmcp.Decode(args, &a); err != nil {
 					return nil, err
 				}
 				if !validStatus(a.Status) {
@@ -153,12 +124,12 @@ func (s *Server) buildTools() []tool {
 		{
 			Name:        "delete_promotion",
 			Description: "Delete a promotion rule by id.",
-			InputSchema: object(props{"id": str("the promotion id")}, []string{"id"}),
-			invoke: func(args json.RawMessage) (any, error) {
+			InputSchema: pmcp.Object(pmcp.Props{"id": pmcp.String("the promotion id")}, []string{"id"}),
+			Invoke: func(_ context.Context, args json.RawMessage) (any, error) {
 				var a struct {
 					ID string `json:"id"`
 				}
-				if err := decode(args, &a); err != nil {
+				if err := pmcp.Decode(args, &a); err != nil {
 					return nil, err
 				}
 				found, err := s.store.Delete(a.ID)
@@ -176,18 +147,18 @@ func (s *Server) buildTools() []tool {
 			Description: "Evaluate the current active promotions against a hypothetical cart total and report the " +
 				"matched discount. cartTotalIncVat is in öre incl. VAT (e.g. 5 000 000 = 50 000 kr). Useful for " +
 				"verifying Volymrabatt tiers without touching a real cart.",
-			InputSchema: object(props{
-				"cartTotalIncVat": integer("cart total incl. VAT, in öre"),
-				"itemQuantity":    integer("optional total item quantity"),
-				"customerSegment": str("optional customer segment"),
+			InputSchema: pmcp.Object(pmcp.Props{
+				"cartTotalIncVat": pmcp.Integer("cart total incl. VAT, in öre"),
+				"itemQuantity":    pmcp.Integer("optional total item quantity"),
+				"customerSegment": pmcp.String("optional customer segment"),
 			}, []string{"cartTotalIncVat"}),
-			invoke: func(args json.RawMessage) (any, error) {
+			Invoke: func(_ context.Context, args json.RawMessage) (any, error) {
 				var a struct {
 					CartTotalIncVat int64  `json:"cartTotalIncVat"`
 					ItemQuantity    int    `json:"itemQuantity"`
 					CustomerSegment string `json:"customerSegment"`
 				}
-				if err := decode(args, &a); err != nil {
+				if err := pmcp.Decode(args, &a); err != nil {
 					return nil, err
 				}
 				g := syntheticCart(a.CartTotalIncVat, a.ItemQuantity, s.defaultVatRate())
@@ -210,19 +181,19 @@ func (s *Server) buildTools() []tool {
 	}
 }

-// syntheticCart builds a one-line cart whose gross total is incVat ore so the
-// promotion engine can be evaluated against an arbitrary total. defaultVatRate
-// is the VAT rate as a float32 percentage (e.g. 25 = 25 %).
-func syntheticCart(incVat int64, qty int, defaultVatRate float32) *cart.CartGrain {
+// syntheticCart builds a one-line cart whose gross total is incVat öre so the
+// promotion engine can be evaluated against an arbitrary total. rateBp is the VAT
+// rate in basis points (2500 = 25%).
+func syntheticCart(incVat int64, qty int, rateBp int) *cart.CartGrain {
 	if qty <= 0 {
 		qty = 1
 	}
-	if defaultVatRate == 0 {
-		defaultVatRate = 25
+	if rateBp == 0 {
+		rateBp = 2500
 	}
 	g := cart.NewCartGrain(0, time.Now())
 	g.Items = []*cart.CartItem{
-		{Id: 1, Sku: "PREVIEW", Quantity: uint16(qty), Price: *cart.NewPriceFromIncVat(incVat, defaultVatRate)},
+		{Id: 1, Sku: "PREVIEW", Quantity: uint16(qty), Price: *cart.NewPriceFromIncVat(incVat, rateBp)},
 	}
 	// Quantity > 1 would multiply the row total; keep the gross equal to incVat by
 	// pricing a single unit at the full total.
@@ -240,55 +211,13 @@ func validStatus(s string) bool {
 	return false
 }

-// ---- result + schema helpers (mirrors the graph-cms MCP edge) -------------
-
-func toolText(v any) map[string]any {
-	b, err := json.Marshal(v)
-	if err != nil {
-		return toolError(err)
-	}
-	return map[string]any{
-		"content": []map[string]any{{"type": "text", "text": string(b)}},
-	}
-}
-
-func toolError(err error) map[string]any {
-	return map[string]any{
-		"isError": true,
-		"content": []map[string]any{{"type": "text", "text": err.Error()}},
-	}
-}
-
-// decode unmarshals tool arguments, tolerating empty/absent arguments.
-func decode(args json.RawMessage, v any) error {
-	if len(args) == 0 || string(args) == "null" {
-		return nil
-	}
-	if err := json.Unmarshal(args, v); err != nil {
-		return fmt.Errorf("invalid arguments: %w", err)
-	}
-	return nil
-}
-
-type props map[string]json.RawMessage
-
-func object(p props, required []string) json.RawMessage {
-	m := map[string]any{
-		"type":       "object",
-		"properties": p,
-	}
-	if len(required) > 0 {
-		m["required"] = required
-	}
-	b, _ := json.Marshal(m)
-	return b
-}
-
-func str(desc string) json.RawMessage  { return scalar("string", desc) }
-func obj(desc string) json.RawMessage  { return scalar("object", desc) }
-func integer(d string) json.RawMessage { return scalar("integer", d) }
-
-func scalar(typ, desc string) json.RawMessage {
-	b, _ := json.Marshal(map[string]any{"type": typ, "description": desc})
-	return b
+// defaultVatRate is the VAT rate used to build the synthetic preview cart when
+// the caller supplies none. Sourced from platform/tax (Nordic standard,
+// defaultCountry SE = 25%) rather than a magic constant.
+//
+// NOTE: reconstructed during the platform/mcp migration (the original method was
+// lost editing this untracked file). Behaviour matches the prior 25% default; if
+// the original read a per-store/configured rate, wire that provider in here.
+func (s *Server) defaultVatRate() int {
+	return tax.NewNordic("").DefaultTaxRate("")
 }