Preserve opaque JSON keys independently of field write guards

internal/platform/canvas_model.go

@@ -95,8 +95,8 @@ func modelJSONSafe(value any, depth int) bool {
 		}
 		return true
 	case map[string]any:
-		for key, item := range value {
-			if canvasChoice(key, "__proto__", "constructor", "prototype") || !modelJSONSafe(item, depth+1) {
+		for _, item := range value {
+			if !modelJSONSafe(item, depth+1) {
 				return false
 			}
 		}

internal/platform/canvas_model_test.go

@@ -102,6 +102,8 @@ func TestCanonicalOperationsPreserveOpaquePayloadAndStableMoveIdentity(t *testin
 	model.Versions[modelChildID] = 1
 	future := modelTestNode("future", modelRootID)
 	future["componentId"], future["dataVersion"], future["data"], future["futureEnvelope"] = "plugin.future", float64(42), map[string]any{"nested": map[string]any{"list": []any{"x", float64(2)}}}, map[string]any{"retain": true}
+	future["data"].(map[string]any)["constructor"] = map[string]any{"retain": true}
+	future["data"].(map[string]any)["__proto__"] = map[string]any{"ordinary": "JSON data"}
 	model.Elements["future"] = future
 	op := modelOperation{ID: modelTestID(1), Changes: []modelChange{{Kind: "field", Target: modelTarget{ID: "a", Incarnation: 1}, Field: "ownerCanvasId", Before: modelJSON(modelRootID), After: modelJSON(modelChildID)}}}
 	after, touched, err := applyModelOperations(model, []modelOperation{op})