ref for projection snapshots

catalog/builder.go

@@ -116,6 +116,7 @@ func Apply(s Schema, source map[string]any) (Projection, error) {
 	}
 
 	p := Projection{
+		ItemID:           uint32Of(source, s.ItemIdField),
 		ID:               id,
 		SKU:              sku,
 		Title:            stringOf(source, s.TitleField),
@@ -180,6 +181,63 @@ func stringOf(m map[string]any, key string) string {
 	return fmt.Sprintf("%v", v)
 }
 
+// uint32Of returns the value at key as a uint32. Best-effort coercion:
+// json.Number / int / int64 / float (integral check) / truthy numeric
+// string. Returns 0 for any missing / non-uint32-representable value —
+// Projection.ItemID = 0 is the documented "no id" signal that the cart's
+// overlay path uses to fall back to PRODUCT_BASE_URL.
+func uint32Of(m map[string]any, key string) uint32 {
+	if key == "" {
+		return 0
+	}
+	v, ok := m[key]
+	if !ok || v == nil {
+		return 0
+	}
+	switch x := v.(type) {
+	case uint32:
+		return x
+	case uint64:
+		if x > 0xFFFFFFFF {
+			return 0 // overflow – treat as unset, downstream falls back
+		}
+		return uint32(x)
+	case int:
+		if x < 0 || x > 0xFFFFFFFF {
+			return 0
+		}
+		return uint32(x)
+	case int64:
+		if x < 0 || x > 0xFFFFFFFF {
+			return 0
+		}
+		return uint32(x)
+	case float64:
+		if x != float64(uint32(x)) || x < 0 || x > 0xFFFFFFFF {
+			return 0 // fractional or out-of-range
+		}
+		return uint32(x)
+	case json.Number:
+		s := x.String()
+		n, err := strconv.ParseUint(s, 10, 32)
+		if err != nil {
+			return 0
+		}
+		return uint32(n)
+	case string:
+		s := strings.TrimSpace(x)
+		if s == "" {
+			return 0
+		}
+		n, err := strconv.ParseUint(s, 10, 32)
+		if err != nil {
+			return 0
+		}
+		return uint32(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.