fix: keep canvas annotation operations idempotent

lib/canvas/agent-mutations.ts

@@ -786,6 +786,13 @@ function applyAddAnnotationOperation(params: {
     const existingAnnotations = Array.isArray(metadata.annotations)
       ? metadata.annotations.filter((item) => item && typeof item === "object")
       : [];
+    const hasExistingOperationAnnotation = existingAnnotations.some(
+      (item) =>
+        (item as Record<string, unknown>).canvasAgentOperationId ===
+        params.plan.operationId
+    );
+    if (hasExistingOperationAnnotation) return;
+
     const nextAnnotations = annotations.map((annotation, index) => ({
       ...annotation,
       id:

tests/routes/canvas-agent-operations.test.ts

@@ -688,6 +688,70 @@ test.describe("canvas agent operation mutation contract", () => {
     ]);
   });
 
+  test("adds annotation metadata to media nodes without duplicating retries", () => {
+    const target = buildImageNode("image-annotated");
+    const plan: CanvasOperationPlan = {
+      version: 1,
+      operationId: "op-add-annotation",
+      operation: "add_annotation",
+      projectId,
+      targetNodeIds: ["image-annotated"],
+      textContent: "背景换浅灰，主体保持不变",
+      annotations: [
+        {
+          type: "box",
+          text: "处理这块背景",
+          bounds: { x: 0.12, y: 0.2, width: 0.5, height: 0.32 },
+          color: "#f59e0b",
+        },
+      ],
+      metadata: {
+        messageId: "assistant-message-annotation",
+        chatId: "chat-1",
+      },
+    };
+
+    const first = applyCanvasOperationPlanToCanvasData({
+      canvasData: getCanvasData([target]),
+      plan,
+    });
+    const annotatedNode = getResultNodes(first.canvasData).find(
+      (node) => node.id === "image-annotated"
+    );
+
+    expect(first.createdNodeIds).toEqual([]);
+    expect(first.updatedNodeIds).toEqual(["image-annotated"]);
+    expect(annotatedNode).toMatchObject({
+      data: {
+        hasAnnotations: true,
+        metadata: {
+          annotations: [
+            expect.objectContaining({
+              id: "op-add-annotation:annotation-image-annotated-1",
+              sourceNodeId: "image-annotated",
+              type: "box",
+              text: "处理这块背景",
+              bounds: { x: 0.12, y: 0.2, width: 0.5, height: 0.32 },
+              createdByAgent: true,
+              canvasAgentOperationId: "op-add-annotation",
+            }),
+          ],
+        },
+      },
+    });
+
+    const retry = applyCanvasOperationPlanToCanvasData({
+      canvasData: first.canvasData,
+      plan,
+    });
+    const retryNode = getResultNodes(retry.canvasData).find(
+      (node) => node.id === "image-annotated"
+    );
+
+    expect(retry.updatedNodeIds).toEqual([]);
+    expect(retryNode.data.metadata.annotations).toHaveLength(1);
+  });
+
   test("keeps batch media writes idempotent by operation id", () => {
     const anchor = buildImageNode("image-anchor");
     const plan = {