fix(canvas): 画布同步 - 素材缺失时可强制覆盖并恢复文本与连线顺序

云端缺少素材时可用本地版强制覆盖，只清失效媒体引用。文本节点不再把资源地址当正文，合并时保留引用槽位顺序。

web/test/canvas-missing-resources.test.ts

@@ -0,0 +1,33 @@
+import { describe, expect, test } from "bun:test";
+
+import { canvasResourceIds, clearMissingCanvasResources } from "@/services/canvas-missing-resources";
+
+describe("canvas missing resource overwrite", () => {
+    test("collects nested resource locators without treating prompt text as media", () => {
+        const value = {
+            nodes: [{ id: "node-1", metadata: { storageKey: "resource:gone", prompt: "resource:keep-as-text", videoPreview: { url: "/api/resources/poster/file" } } }],
+        };
+        expect(canvasResourceIds(value)).toEqual(new Set(["gone", "poster"]));
+    });
+
+    test("removes only invalid media fields and asset binding while keeping node content", () => {
+        const value = {
+            id: "canvas",
+            nodes: [{ id: "node-1", type: "image", metadata: { assetId: "asset-1", storageKey: "resource:gone", content: "/api/resources/gone/file", prompt: "keep this prompt", status: "success" } }],
+            timeline: { clips: [{ id: "clip", directMedia: { kind: "image", assetId: "asset-1", storageKey: "resource:gone", url: "/api/resources/gone/file" } }] },
+        };
+        const repaired = clearMissingCanvasResources(value, new Set(["gone"]));
+        expect(repaired).toEqual({
+            id: "canvas",
+            nodes: [{ id: "node-1", type: "image", metadata: { prompt: "keep this prompt", status: "idle" } }],
+            timeline: { clips: [{ id: "clip", directMedia: { kind: "image" } }] },
+        });
+    });
+
+    test("server reported locator fields are also cleared during the fallback", () => {
+        const value = { nodes: [{ id: "node-1", metadata: { assetId: "asset-1", futureLocator: "resource:gone", prompt: "keep" } }] };
+        expect(clearMissingCanvasResources(value, new Set(["gone"]), "", true)).toEqual({
+            nodes: [{ id: "node-1", metadata: { assetId: "asset-1", prompt: "keep" } }],
+        });
+    });
+});