fix(google): reset Gemini fallback on provider switch, reuse sync client

- Switching from google/google-vertex to another provider resets the
  auto-set Gemini fallback model to glm-4p5 unless --fallback-model is given.
- call_google reuses one sync genai client per credential set instead of
  building a client per call; agent-loop models still get a fresh client.
- The non-top-tier cluster model hint now names current model families.

Author: anhnh2002

codewiki/cli/commands/config.py

@@ -733,7 +733,7 @@ def config_validate(quick: bool, verbose: bool):
             # Warn about non-top-tier cluster model
             if not is_top_tier_model(config.cluster_model):
                 click.secho(
-                    "⚠️  Cluster model is not top-tier. Consider using claude-sonnet-4 or gpt-4.",
+                    "⚠️  Cluster model is not top-tier. Consider a Claude Sonnet/Opus, GPT-5 or Gemini 3 model.",
                     fg="yellow",
                 )
 

codewiki/cli/config_manager.py

@@ -194,6 +194,10 @@ def save(
                     agent_instructions=AgentInstructions(),
                 )
 
+        from codewiki.src.be.backend import is_caw_provider, is_google_provider, needs_base_url
+
+        was_google = is_google_provider(self._config.provider)
+
         # Update fields if provided
         if base_url is not None:
             self._config.base_url = base_url
@@ -238,7 +242,6 @@ def save(
         # Caw providers only need main_model; API providers need base_url +
         # cluster_model on top of that.  The validate() method itself routes
         # by provider, so we only gate on whether enough is set to validate.
-        from codewiki.src.be.backend import is_caw_provider, is_google_provider, needs_base_url
 
         # The glm-4p5 default fallback does not exist on Google endpoints; a
         # fallback that 404s only after the main model failed hides the real error.
@@ -248,6 +251,11 @@ def save(
             and self._config.fallback_model in ("", "glm-4p5")
         ):
             self._config.fallback_model = self._config.main_model
+        # Leaving Google: the Gemini fallback set above would 404 on the new endpoint.
+        elif (
+            was_google and not is_google_provider(self._config.provider) and fallback_model is None
+        ):
+            self._config.fallback_model = "glm-4p5"
 
         if is_caw_provider(self._config.provider):
             if self._config.main_model:

codewiki/src/be/google_provider.py

@@ -95,6 +95,24 @@ def _client_for(config) -> genai.Client:
     )
 
 
+# One-shot calls reuse a sync client per credential set. Agent-loop models get a
+# fresh client (_client_for): their async transport is bound to the event loop.
+_SYNC_CLIENTS: dict[tuple[str, str | None, str, str], genai.Client] = {}
+
+
+def _sync_client_for(config) -> genai.Client:
+    key = (
+        config.provider,
+        config.llm_api_key,
+        getattr(config, "google_project", ""),
+        getattr(config, "google_location", ""),
+    )
+    client = _SYNC_CLIENTS.get(key)
+    if client is None:
+        client = _SYNC_CLIENTS[key] = _client_for(config)
+    return client
+
+
 def create_google_model(config, model_name: str) -> GoogleModel:
     """GoogleModel for the agent loop. No temperature and no thinking config:
     the model defaults apply (Google advises temperature 1.0 for Gemini 3)."""
@@ -159,7 +177,7 @@ def call_google(
     output is logged and returned as None, never raised.
     """
     name = normalise_model_name(model)
-    client = _client_for(config)
+    client = _sync_client_for(config)
     response = client.models.generate_content(
         model=name,
         contents=prompt,

tests/test_google_config.py

@@ -233,3 +233,19 @@ def test_show_vertex_lists_project_and_location(tmp_config):
 
 def test_gemini_3_is_top_tier():
     assert is_top_tier_model(MODEL) is True
+
+
+def test_leaving_google_resets_gemini_fallback(tmp_config):
+    manager = cm.ConfigManager()
+    manager.save(provider="google-vertex", main_model=MODEL, cluster_model=MODEL)
+    assert manager.get_config().fallback_model == MODEL
+
+    manager.save(provider="openai-compatible", base_url="https://api.example.com/v1")
+    assert manager.get_config().fallback_model == "glm-4p5"
+
+
+def test_leaving_google_keeps_explicit_fallback(tmp_config):
+    manager = cm.ConfigManager()
+    manager.save(provider="google-vertex", main_model=MODEL, cluster_model=MODEL)
+    manager.save(provider="openai-compatible", fallback_model="gpt-5-mini")
+    assert manager.get_config().fallback_model == "gpt-5-mini"

tests/test_google_provider.py

@@ -139,6 +139,7 @@ def generate_content(self, **kwargs):
 def fake_models(monkeypatch):
     def install(response):
         models = FakeModels(response)
+        monkeypatch.setattr(google_provider, "_SYNC_CLIENTS", {})
         monkeypatch.setattr(
             google_provider, "_client_for", lambda config: SimpleNamespace(models=models)
         )
@@ -214,3 +215,15 @@ def test_cost_unknown_model_is_omitted(fake_models, monkeypatch):
     )
     messages = [priced, ModelRequest(parts=[UserPromptPart("x")]), priced]
     assert google_provider.messages_cost(messages) == 1.0
+
+
+def test_call_google_reuses_sync_client(monkeypatch):
+    built = []
+    monkeypatch.setattr(google_provider, "_SYNC_CLIENTS", {})
+    monkeypatch.setattr(google_provider, "_client_for", lambda config: built.append(1) or object())
+    config = SimpleNamespace(
+        provider="google-vertex", llm_api_key=None, google_project="p", google_location="eu"
+    )
+    first = google_provider._sync_client_for(config)
+    assert google_provider._sync_client_for(config) is first
+    assert len(built) == 1