diff --git a/client/src/components/Chat/Messages/Content/Parts/__tests__/ArtifactRouting.test.tsx b/client/src/components/Chat/Messages/Content/Parts/__tests__/ArtifactRouting.test.tsx
index 4b6c93ae92..305c117532 100644
--- a/client/src/components/Chat/Messages/Content/Parts/__tests__/ArtifactRouting.test.tsx
+++ b/client/src/components/Chat/Messages/Content/Parts/__tests__/ArtifactRouting.test.tsx
@@ -11,6 +11,11 @@ jest.mock('~/hooks', () => ({
     () =>
     (key: string): string =>
       key,
+  /* `FileAttachment` calls this hook unconditionally to bridge the
+   * two-phase preview lifecycle into the attachment cache. The
+   * routing tests don't exercise the preview flow itself — stub it
+   * to a no-op so it doesn't blow up jsdom rendering. */
+  useAttachmentPreviewSync: () => ({ status: 'ready', previewError: undefined, isPolling: false }),
 }));
 
 jest.mock('../LogLink', () => ({
diff --git a/client/src/components/Chat/Messages/Content/Parts/__tests__/TextAttachment.test.tsx b/client/src/components/Chat/Messages/Content/Parts/__tests__/TextAttachment.test.tsx
index c5a8369796..fcadf31005 100644
--- a/client/src/components/Chat/Messages/Content/Parts/__tests__/TextAttachment.test.tsx
+++ b/client/src/components/Chat/Messages/Content/Parts/__tests__/TextAttachment.test.tsx
@@ -13,6 +13,10 @@ jest.mock('~/hooks', () => ({
       };
       return translations[key] ?? key;
     },
+  /* `FileAttachment` calls this hook unconditionally to bridge the
+   * two-phase preview lifecycle. Stub to a no-op for tests that
+   * don't exercise the preview flow. */
+  useAttachmentPreviewSync: () => ({ status: 'ready', previewError: undefined, isPolling: false }),
 }));
 
 const mockHandleDownload = jest.fn();