fix(canvas): 预演合并 - 场景时间戳采用服务端快照，带 id 数组按条目合并

每次预演变更都会改 updatedAt，不再把它当成用户编辑冲突；带 id 的对象数组按条目合并，仅刷新场景时保留本地视口。

web/test/agent-canvas-patch.test.ts

@@ -68,12 +68,60 @@ test("task progress ahead of the server checkpoint still accepts terminal state"
     expect(isCanvasNodeGenerating(result.nodes[0])).toBe(false);
 });
 
-test("full Agent refresh removes unchanged nodes but preserves conflicting local edits", () => {
-    const remaining = { ...node, id: "remaining", metadata: {} };
-    const previous = { ...project, nodes: [node, remaining] };
-    const incoming = { ...previous, nodes: [remaining] };
-    expect(mergeAgentCanvasEditor(previous, incoming, previous.nodes, []).nodes).toEqual([remaining]);
-    const local = { ...node, title: "Unsaved local title" };
-    expect(() => mergeAgentCanvasEditor(previous, incoming, [local, remaining], [])).toThrow("冲突");
-    expect(local.title).toBe("Unsaved local title");
+test("full Previs refresh merges scene bookkeeping and preserves the local viewport", () => {
+    const scene = {
+        id: "scene-1",
+        version: 1 as const,
+        title: "镜头",
+        background: "#111111",
+        environmentIntensity: 0.7,
+        environment: { mode: "color" as const },
+        gridVisible: true,
+        objects: [],
+        cameras: [],
+        lights: [],
+        shots: [],
+        activeShotId: "shot-1",
+        createdAt: "2026-09-13T00:00:00Z",
+        updatedAt: "2026-09-13T00:00:00Z",
+    };
+    const previous = { ...project, previsScenes: [scene] };
+    const incoming = {
+        ...previous,
+        revision: 2,
+        updatedAt: "2026-09-13T12:00:00Z",
+        previsScenes: [{ ...scene, updatedAt: "2026-09-13T12:00:00Z", objects: [{ id: "actor-1", name: "Agent 演员" }] }],
+    };
+    const local = {
+        ...previous,
+        viewport: { x: -480, y: -220, k: 0.72 },
+        previsScenes: [{ ...scene, updatedAt: "2026-09-13T11:59:00Z" }],
+    };
+    const merged = mergeAgentCanvasEditor(previous, incoming, local.nodes, local.connections, local);
+    expect(merged.previsScenes[0].objects).toEqual(incoming.previsScenes[0].objects);
+    expect(merged.previsScenes[0].updatedAt).toBe(incoming.previsScenes[0].updatedAt);
+    expect(merged.viewport).toEqual(local.viewport);
+});
+
+test("full Previs refresh still rejects a same-field scene edit", () => {
+    const scene = {
+        id: "scene-1",
+        version: 1 as const,
+        title: "镜头",
+        background: "#111111",
+        environmentIntensity: 0.7,
+        environment: { mode: "color" as const },
+        gridVisible: true,
+        objects: [],
+        cameras: [],
+        lights: [],
+        shots: [],
+        activeShotId: "shot-1",
+        createdAt: "2026-09-13T00:00:00Z",
+        updatedAt: "2026-09-13T00:00:00Z",
+    };
+    const previous = { ...project, previsScenes: [scene] };
+    const incoming = { ...previous, revision: 2, previsScenes: [{ ...scene, title: "云端镜头", updatedAt: "2026-09-13T12:00:00Z" }] };
+    const local = { ...previous, previsScenes: [{ ...scene, title: "本地镜头", updatedAt: "2026-09-13T11:59:00Z" }] };
+    expect(() => mergeAgentCanvasEditor(previous, incoming, local.nodes, local.connections, local)).toThrow("冲突");
 });