diff --git a/catalog/builder.go b/catalog/builder.go
index f7a19f7..fe046b5 100644
--- a/catalog/builder.go
+++ b/catalog/builder.go
@@ -143,6 +143,9 @@ func Apply(s Schema, source map[string]any) (Projection, error) {
 		TaxClass:         tax,
 		InventoryTracked: boolOf(source, s.InventoryTrackedF, truthy),
 		DropShip:         boolOf(source, s.DropShipF, truthy),
+		SellerID:         uint32Of(source, s.SellerIdField),
+		SellerName:       stringOf(source, s.SellerNameField),
+		LeadTimeDays:     intOf(source, s.LeadTimeField),
 		Category:         stringOf(source, s.CategoryField),
 		Category2:        stringOf(source, s.Category2Field),
 		Category3:        stringOf(source, s.Category3Field),
@@ -260,11 +263,57 @@ func uint32Of(m map[string]any, key string) uint32 {
 	return 0
 }
 
+// intOf returns the value at key as an int (floor for fractional floats).
+// Missing / non-numeric / negative values return 0 — Projection.LeadTimeDays
+// = 0 is the documented "unset" signal, mirroring uint32Of's contract.
+func intOf(m map[string]any, key string) int {
+	if key == "" {
+		return 0
+	}
+	v, ok := m[key]
+	if !ok || v == nil {
+		return 0
+	}
+	switch x := v.(type) {
+	case int:
+		if x < 0 {
+			return 0
+		}
+		return x
+	case int64:
+		if x < 0 {
+			return 0
+		}
+		return int(x)
+	case float64:
+		if x < 0 {
+			return 0
+		}
+		return int(x)
+	case json.Number:
+		n, err := x.Int64()
+		if err != nil || n < 0 {
+			return 0
+		}
+		return int(n)
+	case string:
+		s := strings.TrimSpace(x)
+		if s == "" {
+			return 0
+		}
+		n, err := strconv.ParseFloat(s, 64)
+		if err != nil || n < 0 {
+			return 0
+		}
+		return int(n)
+	}
+	return 0
+}
+
 // boolOf returns the value at key coerced through truthy. nil/missing keys
 // are false; strings lower-cased and matched against truthy; bools passed
 // through; numerics "!= 0"; json.Number goes through Float64.
-func boolOf(m map[string]any, key string, truthy []string) bool {
-	if key == "" {
+func boolOf(m map[string]any, key string, truthy []string) bool {	if key == "" {
 		return false
 	}
 	v, ok := m[key]
diff --git a/catalog/builder_test.go b/catalog/builder_test.go
index 8755977..5635551 100644
--- a/catalog/builder_test.go
+++ b/catalog/builder_test.go
@@ -15,12 +15,12 @@ import (
 func TestBuilderJSONNumber(t *testing.T) {
 	// json.Number for SKU
 	src := map[string]any{
-		"sku":            json.Number("123456789012345"), // float64-unsafe
-		"title":          "BigNumber SKU",
-		"price_inc_vat":  json.Number("14995"), // already øre
-		"currency":       "SEK",
-		"tax_class":      "standard",
-		"updated_at":     json.Number("1700000000000"),
+		"sku":           json.Number("123456789012345"), // float64-unsafe
+		"title":         "BigNumber SKU",
+		"price_inc_vat": json.Number("14995"), // already øre
+		"currency":      "SEK",
+		"tax_class":     "standard",
+		"updated_at":    json.Number("1700000000000"),
 	}
 	p, err := Apply(DefaultSchema(), src)
 	if err != nil {
@@ -193,3 +193,99 @@ func TestBuilderFractionalStringPriceCorrectScale(t *testing.T) {
 		t.Errorf("PriceIncVat: got %d want %d", p.PriceIncVat, 14995)
 	}
 }
+
+// Drop-ship routing carriers (docs/plan-dropship.md Phase 1): seller id /
+// name / lead time coerce from per-tenant source keys via Schema overrides,
+// mirroring how the live feed emits supplierName-style keys. Zero values
+// (missing keys, negative numbers, junk strings) must stay at the documented
+// "unset" signals rather than erroring — one bad item can't poison a batch.
+func TestBuilderDropshipCarriers(t *testing.T) {
+	s := DefaultSchema()
+	s.SellerIdField = "supplierId"
+	s.SellerNameField = "supplierName"
+	s.LeadTimeField = "deliveryTime"
+
+	p, err := Apply(s, map[string]any{
+		"sku":           "X-1",
+		"price_inc_vat": int64(100_00),
+		"updated_at":    int64(1700000000000),
+		"drop_ship":     true,
+		"supplierId":    4711,
+		"supplierName":  "Bygg Import AB",
+		"deliveryTime":  3,
+	})
+	if err != nil {
+		t.Fatalf("apply with dropship carriers: %v", err)
+	}
+	if !p.DropShip {
+		t.Error("DropShip: got false, want true")
+	}
+	if p.SellerID != 4711 {
+		t.Errorf("SellerID: got %d, want 4711", p.SellerID)
+	}
+	if p.SellerName != "Bygg Import AB" {
+		t.Errorf("SellerName: got %q", p.SellerName)
+	}
+	if p.LeadTimeDays != 3 {
+		t.Errorf("LeadTimeDays: got %d, want 3", p.LeadTimeDays)
+	}
+
+	// Missing keys → unset signals, no error.
+	p, err = Apply(s, map[string]any{
+		"sku":           "X-2",
+		"price_inc_vat": int64(100_00),
+		"updated_at":    int64(1700000000000),
+	})
+	if err != nil {
+		t.Fatalf("apply without dropship carriers: %v", err)
+	}
+	if p.DropShip || p.SellerID != 0 || p.SellerName != "" || p.LeadTimeDays != 0 {
+		t.Errorf("unset carriers should zero: %+v", p)
+	}
+
+	// Junk shapes floor to unset, never fail the build.
+	for name, bad := range map[string]any{
+		"negative id": -5,
+		"string id":   "not-a-number",
+		"float id":    1.5,
+	} {
+		p, err = Apply(s, map[string]any{
+			"sku": "X-3", "price_inc_vat": int64(100_00),
+			"updated_at": int64(1700000000000),
+			"supplierId": bad,
+		})
+		if err != nil {
+			t.Fatalf("%s: apply should not fail on junk carrier: %v", name, err)
+		}
+		if p.SellerID != 0 {
+			t.Errorf("%s: SellerID should be 0, got %d", name, p.SellerID)
+		}
+	}
+
+	// Wire round-trip: new fields survive Encode/Decode for consumers that
+	// never rebuilt.
+	b, err := p.Encode()
+	if err != nil {
+		t.Fatalf("encode: %v", err)
+	}
+	rt, err := Decode(b)
+	if err != nil {
+		t.Fatalf("decode: %v", err)
+	}
+	if rt.SKU != p.SKU || rt.DropShip || rt.SellerID != 0 {
+		t.Errorf("round-trip mismatch: %+v vs %+v", rt, p)
+	}
+
+	// json.Number lead time (UseNumber producers).
+	p, err = Apply(s, map[string]any{
+		"sku": "X-4", "price_inc_vat": int64(100_00),
+		"updated_at":   int64(1700000000000),
+		"deliveryTime": json.Number("7"),
+	})
+	if err != nil {
+		t.Fatalf("json.Number lead time: %v", err)
+	}
+	if p.LeadTimeDays != 7 {
+		t.Errorf("LeadTimeDays from json.Number: got %d, want 7", p.LeadTimeDays)
+	}
+}
diff --git a/catalog/projection.go b/catalog/projection.go
index 27fe067..42eb7d2 100644
--- a/catalog/projection.go
+++ b/catalog/projection.go
@@ -18,6 +18,9 @@
 //	tax_class        ← source[TaxClassField]         (string identifier)
 //	inventory_tracked ← bool coercion of source[InventoryTrackedField]
 //	drop_ship        ← bool coercion of source[DropShipField]
+//	seller_id        ← uint32 coercion of source[SellerIdField]  (0 = unset)
+//	seller_name      ← source[SellerNameField]       (omitempty)
+//	lead_time_days   ← int coercion of source[LeadTimeField]     (0 = unset)
 //	category         ← source[CategoryField]          (omitempty)
 //	category2        ← source[Category2Field]         (omitempty)
 //	category3        ← source[Category3Field]         (omitempty)
@@ -103,6 +106,15 @@ type Projection struct {
 	TaxClass         string          `json:"tax_class"`
 	InventoryTracked bool            `json:"inventory_tracked"`
 	DropShip         bool            `json:"drop_ship"`
+	// Drop-ship routing carriers (Phase 1 of docs/plan-dropship.md).
+	// SellerID mirrors AddItem.ItemId coercion rules: 0 = "producer didn't
+	// publish" and downstream keeps whatever the HTTP fallback fetched.
+	// SellerName is what checkout writes into order-line
+	// Properties["supplier"] (the dropship-fulfill flow groups on it).
+	// LeadTimeDays is supplier lead time in days, 0 = unset.
+	SellerID     uint32 `json:"seller_id,omitempty"`
+	SellerName   string `json:"seller_name,omitempty"`
+	LeadTimeDays int    `json:"lead_time_days,omitempty"`
 	Category         string          `json:"category,omitempty"`
 	Category2        string          `json:"category2,omitempty"`
 	Category3        string          `json:"category3,omitempty"`
diff --git a/catalog/schema.go b/catalog/schema.go
index 2c0659a..159cfd6 100644
--- a/catalog/schema.go
+++ b/catalog/schema.go
@@ -58,6 +58,15 @@ type Schema struct {
 	TaxClassField     string `json:"tax_class_field,omitempty"`
 	InventoryTrackedF string `json:"inventory_tracked_field,omitempty"`
 	DropShipF         string `json:"drop_ship_field,omitempty"`
+	// SellerIdField / SellerNameField name the source keys carrying the
+	// drop-ship supplier identity. SellerId coerces to uint32 (0 = unset);
+	// SellerName is the human-facing name checkout writes into order-line
+	// Properties["supplier"]. Empty field = carrier not published.
+	SellerIdField   string `json:"seller_id_field,omitempty"`
+	SellerNameField string `json:"seller_name_field,omitempty"`
+	// LeadTimeField names the source key carrying supplier lead time in
+	// days (numeric; fractional values floor). Empty = not published.
+	LeadTimeField string `json:"lead_time_field,omitempty"`
 	CategoryField     string `json:"category_field,omitempty"`
 	Category2Field    string `json:"category2_field,omitempty"`
 	Category3Field    string `json:"category3_field,omitempty"`
@@ -128,6 +137,9 @@ func DefaultSchema() Schema {
 		TaxClassField:     "tax_class",
 		InventoryTrackedF: "inventory_tracked",
 		DropShipF:         "drop_ship",
+		SellerIdField:     "seller_id",
+		SellerNameField:   "seller_name",
+		LeadTimeField:     "lead_time_days",
 		CategoryField:     "category",
 		Category2Field:    "category2",
 		Category3Field:    "category3",