diff --git a/extension/src/background.test.ts b/extension/src/background.test.ts
index e45614843..84c61fab5 100644
--- a/extension/src/background.test.ts
+++ b/extension/src/background.test.ts
@@ -877,6 +877,30 @@ describe('background tab isolation', () => {
     expect(mod.__test__.getReconnectAttempts()).toBe(0);
   });
 
+  it('pings without credentials and logs a non-OK status instead of swallowing it', async () => {
+    const { chrome } = createChromeMock();
+    vi.stubGlobal('chrome', chrome);
+    const warnSpy = vi.spyOn(console, 'warn').mockImplementation(() => {});
+    const fetchMock = vi.fn(async () => ({ ok: false, status: 431 }));
+    vi.stubGlobal('fetch', fetchMock);
+
+    await import('./background');
+
+    await vi.waitFor(() => {
+      expect(fetchMock).toHaveBeenCalled();
+    });
+
+    // The ping must not attach the localhost cookie jar — that is what pushes
+    // the request past Node's header limit and makes the daemon answer 431.
+    expect(fetchMock.mock.calls[0][1]).toMatchObject({ credentials: 'omit' });
+    // A non-OK ping must be logged, not silently swallowed.
+    expect(warnSpy).toHaveBeenCalledWith(expect.stringContaining('HTTP 431'));
+    // The WebSocket must not be attempted after a failed ping.
+    expect(MockWebSocket.instances).toHaveLength(0);
+
+    warnSpy.mockRestore();
+  });
+
   it('ignores daemon commands delivered to a superseded WebSocket', async () => {
     const { chrome } = createChromeMock();
     vi.stubGlobal('chrome', chrome);
diff --git a/extension/src/background.ts b/extension/src/background.ts
index 4918894c2..1bdbfc08e 100644
--- a/extension/src/background.ts
+++ b/extension/src/background.ts
@@ -138,14 +138,24 @@ async function connectAttempt(): Promise<void> {
   if (isDaemonSocketActive()) return;
 
   try {
-    const res = await fetch(DAEMON_PING_URL, { signal: AbortSignal.timeout(1000) });
+    // omit credentials so the browser doesn't attach the localhost cookie jar —
+    // a large jar can push the request past Node's default header limit and make
+    // the daemon answer 431, silently wedging the connect loop forever.
+    const res = await fetch(DAEMON_PING_URL, {
+      signal: AbortSignal.timeout(1000),
+      credentials: 'omit',
+    });
     if (!res.ok) {
+      console.warn(`[opencli] daemon ping failed: HTTP ${res.status}`);
       scheduleReconnect();
       return; // unexpected response — not our daemon, but keep polling.
     }
     // Daemon is reachable — proceed straight to the WebSocket below.
     reconnectAttempts = 0;
   } catch {
+    // Daemon not running is the expected idle state — keep the probe silent to
+    // avoid per-poll service-worker noise (see connect() docstring). The 431
+    // wedge this fixes is surfaced in the !res.ok branch above.
     scheduleReconnect();
     return; // daemon not running — keep polling until the next daemon spawn.
   }