fix(app,canvas): 图片档位并集忽略停用线路，重生结果不再继承旧素材绑定

前台分辨率并集只收启用且权重大于 0 的供应线路，避免停用 4K 线路后仍出现不可路由档位。生成回写新媒体时清除旧 assetId，堵住原地重生后「旧素材 + 新资源」配对。

Co-authored-by: Cursor <cursoragent@cursor.com>

web/test/canvas-generation-task-sync.test.ts

@@ -0,0 +1,37 @@
+import { describe, expect, test } from "bun:test";
+
+import { applyGeneratedMediaResultMetadata, videoMetadata } from "@/lib/canvas/canvas-generation-task-sync";
+import { CanvasNodeType, type CanvasNodeData } from "@/types/canvas";
+
+function videoNode(assetId: string, storageKey: string): CanvasNodeData {
+    return {
+        id: "node-1",
+        type: CanvasNodeType.Video,
+        title: "镜头",
+        position: { x: 0, y: 0 },
+        width: 320,
+        height: 180,
+        metadata: { assetId, storageKey, content: "https://example.test/old.mp4", prompt: "旧提示词" },
+    };
+}
+
+describe("applyGeneratedMediaResultMetadata", () => {
+    test("clears the previous asset binding when a regenerated media result lands", () => {
+        const node = videoNode("asset-old", "video:old");
+        const next = applyGeneratedMediaResultMetadata(node, videoMetadata({
+            url: "https://example.test/new.mp4",
+            storageKey: "video:new",
+            width: 1280,
+            height: 720,
+            bytes: 12,
+            mimeType: "video/mp4",
+            durationMs: 4000,
+        }), { prompt: "新提示词" });
+
+        expect(next.assetId).toBeUndefined();
+        expect(next.storageKey).toBe("video:new");
+        expect(next.content).toBe("https://example.test/new.mp4");
+        expect(next.prompt).toBe("新提示词");
+        expect(next.status).toBe("success");
+    });
+});