fix(webui): validate inferred file paths before preview (#4935)

webui/src/tests/thread-shell.test.tsx

@@ -231,6 +231,59 @@ describe("ThreadShell", () => {
     );
   });
 
+  it("keeps inferred file paths non-interactive when the availability probe fails", async () => {
+    const client = makeClient();
+    let resolveProbe!: (value: Response) => void;
+    const probe = new Promise<Response>((resolve) => {
+      resolveProbe = resolve;
+    });
+    const fetchMock = vi.fn((input: RequestInfo | URL) => {
+      const url = String(input);
+      if (url.includes("websocket%3Apreview-error/webui-thread")) {
+        return Promise.resolve(httpJson(transcriptFromSimpleMessages([
+          { role: "assistant", content: "Unreadable file: `prompts/dream.md`" },
+        ])));
+      }
+      if (url.includes("websocket%3Apreview-error/file-preview?")) return probe;
+      return Promise.resolve({
+        ok: false,
+        status: 404,
+        json: async () => ({}),
+      });
+    });
+    vi.stubGlobal("fetch", fetchMock);
+
+    render(wrap(
+      client,
+      <ThreadShell
+        session={session("preview-error")}
+        title="Preview error"
+        onToggleSidebar={() => {}}
+      />,
+    ));
+
+    const reference = await screen.findByTestId("inline-file-path");
+    await waitFor(() => expect(fetchMock).toHaveBeenCalledWith(
+      expect.stringContaining("file-preview?path=prompts%2Fdream.md&probe=1"),
+      expect.anything(),
+    ));
+    await act(async () => {
+      resolveProbe({
+        ok: false,
+        status: 500,
+        text: async () => "failed to read file",
+        json: async () => ({}),
+      } as Response);
+      await probe;
+      await Promise.resolve();
+    });
+
+    expect(reference).not.toHaveAttribute("role");
+    expect(reference).not.toHaveAttribute("tabindex");
+    fireEvent.click(reference);
+    expect(screen.queryByText("failed to read file")).not.toBeInTheDocument();
+  });
+
   it("does not navigate away when clicking the chat title", async () => {
     const client = makeClient();
     const onGoHome = vi.fn();