fix(google-chat): avoid guessing auth failure cause

plugins/platforms/google_chat/adapter.py

@@ -690,7 +690,10 @@ class GoogleChatAdapter(BasePlatformAdapter):
         """Run streaming_pull with exponential backoff + full jitter; fatal after N attempts.
         ``subscribe()`` returns a Future that resolves when the stream dies."""
         pubsub_fatals = {
-            gax_exceptions.Unauthenticated: ("pubsub_auth", "Pub/Sub authentication failed (SA key invalid/revoked)"),
+            gax_exceptions.Unauthenticated: (
+                "pubsub_auth",
+                "Pub/Sub authentication failed; check service-account credentials and gateway logs",
+            ),
             gax_exceptions.PermissionDenied: ("pubsub_permission", "SA lacks pubsub.subscriber on the subscription"),
         }
         attempt = 0

tests/gateway/test_google_chat.py

@@ -1518,6 +1518,22 @@ class TestADCFallback:
 
 
 class TestSupervisorReconnect:
+    @pytest.mark.asyncio
+    async def test_unauthenticated_status_does_not_guess_credential_cause(
+        self, adapter
+    ):
+        """An auth rejection may have causes other than a revoked SA key."""
+        adapter._subscriber.subscribe.side_effect = (
+            _gc_mod.gax_exceptions.Unauthenticated("request rejected")
+        )
+
+        await adapter._run_supervisor()
+
+        assert adapter.fatal_error_code == "pubsub_auth"
+        assert adapter.fatal_error_message == (
+            "Pub/Sub authentication failed; check service-account credentials and gateway logs"
+        )
+
     @pytest.mark.asyncio
     async def test_fatal_after_max_retries(self, adapter, monkeypatch):
         """Simulate 10+ failing subscribe() calls and assert fatal error set."""