fix: keep background removal out of canvas deletion

lib/canvas/agent-model-planner.ts

@@ -140,6 +140,11 @@ function getDecisionNodeIds(params: {
 
 function inferHighRiskOperation(userText: string) {
   const text = userText.toLowerCase();
+  if (
+    /删除背景|删掉背景|去掉背景|去背景|移除背景|抠图|去背/.test(text)
+  ) {
+    return "";
+  }
   if (
     /删除|删掉|删了|删去|移除/.test(text) ||
     /清空(?:画布|选中|当前|节点|对象|元素|这些|全部)/.test(text) ||

tests/routes/canvas-chat-helpers.test.ts

@@ -696,6 +696,12 @@ test.describe("canvas chat pure helpers", () => {
         context: plannerContext,
       })
     ).toBe(false);
+    expect(
+      shouldConsiderCanvasAgentModelPlanner({
+        userText: "删除背景，结果放右边",
+        context: plannerContext,
+      })
+    ).toBe(false);
     expect(
       shouldConsiderCanvasAgentModelPlanner({
         userText: "新建一个视频槽位",
@@ -1731,6 +1737,22 @@ test.describe("canvas chat pure helpers", () => {
       riskOperation: "delete_nodes",
       targetNodeIds: ["image-1", "text-1"],
     });
+
+    const removeBackgroundOutcome = normalizeCanvasAgentModelPlannerDecision({
+      decision: {
+        action: "none",
+      },
+      context: plannerContext,
+      projectId: plannerContext.projectId || "",
+      messageId: "message-1",
+      chatId: "chat-1",
+      userText: "删除背景，结果放右边",
+    });
+
+    expect(removeBackgroundOutcome).toEqual({
+      kind: "none",
+      reason: undefined,
+    });
   });
 
   test("builds pending move-node operation from model-planned high-risk layout", () => {