diff --git a/.project-docs/30-worklog/tasks/20260806-video-source-picker-4d8a.md b/.project-docs/30-worklog/tasks/20260806-video-source-picker-4d8a.md
new file mode 100644
index 0000000..4853e70
--- /dev/null
+++ b/.project-docs/30-worklog/tasks/20260806-video-source-picker-4d8a.md
@@ -0,0 +1,43 @@
+# Task: 修复作品图片选择与视频首帧附件提交
+
+## Identity
+
+- Task ID: 20260806-video-source-picker-4d8a
+- Mode: Feature
+- Branch: codex/fix-video-source-selection
+- Worktree: D:\Datas\OthersProjects\makelore-video-source-selection
+- Base commit: 929b12485257e03faa45495a8eb429b63fdec038
+- Owner: codex
+- Status: Completed
+
+## Scope
+
+- 修复从作品列表选择视频首帧后弹窗持续停留的问题。
+- 保持 `resultAssets[].assetId` 到 Gateway `attachment_asset_ids` 的现有传递链路。
+- 增加慢 Agent 响应场景的回归测试。
+
+## Intent And Constraints
+
+- 用户确认选择后立即关闭弹窗，不等待整轮 Agent 响应。
+- Agent 请求失败时在主对话区展示错误，不把错误留在已关闭弹窗中。
+- 不触碰原客户端工作区中的其他未提交改动。
+
+## Outcome
+
+- 作品图片选择后弹窗立即关闭，同时继续提交真实 Asset ID。
+- 请求失败会回到对话区错误提示，用户仍可重新选择。
+- 回归测试覆盖 Agent Promise 未完成时的弹窗状态。
+
+## Verification
+
+- `vitest image-canvas-page + works-square-design-workspace`：38 passed。
+- `pnpm typecheck`：通过。
+- `pnpm build:vite`：通过（仅保留既有 chunk 体积提示）。
+
+## Follow-ups
+
+- None recorded.
+
+## Promotion Candidates
+
+- None recorded.
diff --git a/src/pages/ImageCanvas/index.tsx b/src/pages/ImageCanvas/index.tsx
index 64d5cef..52c4fd6 100644
--- a/src/pages/ImageCanvas/index.tsx
+++ b/src/pages/ImageCanvas/index.tsx
@@ -547,15 +547,14 @@ export function ImageCanvas() {
     const requestedWorkspaceId = workspace.workspaceId;
     setFirstFrameBusyKey(asset.assetId);
     setFirstFrameError(null);
+    setActionError(null);
     setSubmitting(true);
+    setFirstFramePickerOpen(false);
     try {
       await sendMessage('使用作品图片作为视频首帧', [asset.assetId]);
-      if (useImageWorkspaceStore.getState().activeWorkspaceId === requestedWorkspaceId) {
-        setFirstFramePickerOpen(false);
-      }
     } catch (error) {
       if (useImageWorkspaceStore.getState().activeWorkspaceId === requestedWorkspaceId) {
-        setFirstFrameError(error instanceof Error ? error.message : String(error));
+        setActionError(error instanceof Error ? error.message : String(error));
       }
     } finally {
       setFirstFrameBusyKey(null);
diff --git a/tests/unit/image-canvas-page.test.tsx b/tests/unit/image-canvas-page.test.tsx
index 688f1de..2b75a91 100644
--- a/tests/unit/image-canvas-page.test.tsx
+++ b/tests/unit/image-canvas-page.test.tsx
@@ -570,6 +570,8 @@ describe('ImageCanvas Workspace-first design experience', () => {
   });
 
   it('submits a successful work Asset id when it is selected as the video first frame', async () => {
+    const pendingSelection = deferred<DesignWorkspace>();
+    sendImageWorkspaceMessageMock.mockReturnValueOnce(pendingSelection.promise);
     fetchImageWorkspaceProjectMock.mockResolvedValueOnce({
       ...workspaceFixture(),
       turnRevision: 2,
@@ -603,6 +605,12 @@ describe('ImageCanvas Workspace-first design experience', () => {
       expect.stringMatching(/^turn-/),
       ['asset-one'],
     ));
+    expect(screen.queryByRole('dialog', { name: '选择视频首帧' })).not.toBeInTheDocument();
+
+    await act(async () => {
+      pendingSelection.resolve(workspaceFixture());
+      await pendingSelection.promise;
+    });
   });
 
   it('uploads a local first-frame image and submits its Asset id to the Agent', async () => {