fix: only show artifact download success after the file is delivered

useAttachmentLink swallows fetch errors (an expired code-output URL or a
404 share download) and resolves without throwing, so the preview-panel
download button flipped to the success checkmark even when no file was
downloaded.

Return a boolean from handleDownload (true once a download is initiated,
false on error/empty response) and only mark the artifact download as
succeeded when a file was actually delivered. The return value is
ignored by the existing onClick callers.

client/src/components/Artifacts/DownloadArtifact.tsx

@@ -71,8 +71,13 @@ const DownloadArtifact = ({ artifact }: { artifact: Artifact }) => {
   const handleDownload = async (event: React.MouseEvent<HTMLButtonElement>) => {
     try {
       if (downloadOriginalFile) {
-        await downloadAttachment(event);
-        markDownloaded();
+        // Only flag success when a file was actually delivered; the
+        // attachment helper swallows fetch errors (e.g. an expired
+        // code-output URL or a 404 share download) and resolves either way.
+        const downloaded = await downloadAttachment(event);
+        if (downloaded) {
+          markDownloaded();
+        }
         return;
       }
       downloadContent();

client/src/components/Artifacts/__tests__/DownloadArtifact.test.tsx

@@ -87,7 +87,9 @@ describe('DownloadArtifact', () => {
   let anchorClick: jest.SpyInstance;
 
   beforeEach(() => {
-    mockFileDownload.mockClear();
+    mockFileDownload.mockReset();
+    // The attachment helper resolves to `true` when a file was delivered.
+    mockFileDownload.mockResolvedValue(true);
     createObjectURL = jest.fn(() => 'blob:mock');
     revokeObjectURL = jest.fn();
     Object.defineProperty(window.URL, 'createObjectURL', {
@@ -107,14 +109,29 @@ describe('DownloadArtifact', () => {
     anchorClick.mockRestore();
   });
 
-  it('downloads the original file (not the preview) for an office artifact', async () => {
-    render(<DownloadArtifact artifact={officeArtifact} />);
+  it('downloads the original file (not the preview) for an office artifact and shows success', async () => {
+    const { container } = render(<DownloadArtifact artifact={officeArtifact} />);
     await act(async () => {
       fireEvent.click(screen.getByRole('button'));
     });
     expect(mockFileDownload).toHaveBeenCalledTimes(1);
     // The preview HTML must NOT be serialized into a blob download.
     expect(createObjectURL).not.toHaveBeenCalled();
+    // A delivered file flips the button to the success checkmark.
+    expect(container.querySelector('.lucide-circle-check-big')).not.toBeNull();
+  });
+
+  it('does NOT show success when the original-file download fails', async () => {
+    // Expired code-output URL / 404 share download: the helper resolves
+    // to false instead of throwing. The checkmark must stay hidden.
+    mockFileDownload.mockResolvedValueOnce(false);
+    const { container } = render(<DownloadArtifact artifact={officeArtifact} />);
+    await act(async () => {
+      fireEvent.click(screen.getByRole('button'));
+    });
+    expect(mockFileDownload).toHaveBeenCalledTimes(1);
+    expect(container.querySelector('.lucide-circle-check-big')).toBeNull();
+    expect(container.querySelector('.lucide-download')).not.toBeNull();
   });
 
   it('serializes content as a blob for a non-file-backed (LLM-authored) artifact', async () => {

client/src/components/Chat/Messages/Content/Parts/LogLink.tsx

@@ -54,7 +54,16 @@ export const useAttachmentLink = ({
   const { refetch: downloadFromApi } = useFileDownload(user, file_id, { source });
   const { refetch: downloadFromUrl } = useCodeOutputDownload(href);
 
-  const handleDownload = async (event: React.MouseEvent<HTMLAnchorElement | HTMLButtonElement>) => {
+  /**
+   * Triggers the download and reports whether a file was actually
+   * delivered: `true` once a download is initiated, `false` on a fetch
+   * error or an empty/denied response (e.g. an expired code-output URL or
+   * a 404 share download). Callers that show success feedback should gate
+   * it on this result rather than on the promise merely resolving.
+   */
+  const handleDownload = async (
+    event: React.MouseEvent<HTMLAnchorElement | HTMLButtonElement>,
+  ): Promise<boolean> => {
     event.preventDefault();
     try {
       // In a shared view, a snapshotted file's href is rewritten to the share
@@ -63,12 +72,12 @@ export const useAttachmentLink = ({
       // original href / code-output path still works when snapshots are disabled.
       if (shareId && file_id && href.startsWith('/api/share/')) {
         triggerDownload(sharedFileDownload(shareId, file_id), filename);
-        return;
+        return true;
       }
 
       if (!useLocalDownload && isHttpDownloadTarget(href)) {
         triggerDownload(href, filename);
-        return;
+        return true;
       }
 
       const stream = useLocalDownload ? await downloadFromApi() : await downloadFromUrl();
@@ -78,11 +87,13 @@ export const useAttachmentLink = ({
           status: 'error',
           message: 'Error downloading file',
         });
-        return;
+        return false;
       }
       triggerDownload(stream.data, filename);
+      return true;
     } catch (error) {
       console.error('Error downloading file:', error);
+      return false;
     }
   };