fix: update runner auth default model to claude-sonnet-4-6

The runner's setup_sdk_authentication() had a hardcoded fallback to
claude-sonnet-4-5 when LLM_MODEL is absent. While the operator always
populates LLM_MODEL, this leaves a cross-component default inconsistent
with models.json, sessions.go, and the ambient-api-server.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: jeremyeder

components/runners/ambient-runner/ambient_runner/bridges/claude/auth.py

@@ -72,8 +72,8 @@ async def setup_sdk_authentication(context: RunnerContext) -> tuple[str, bool, s
     model = context.get_env("LLM_MODEL")
 
     # Default model differs: Vertex AI uses @date suffixes, Anthropic API does not
-    DEFAULT_MODEL = "claude-sonnet-4-5"
-    DEFAULT_VERTEX_MODEL = "claude-sonnet-4-5@20250929"
+    DEFAULT_MODEL = "claude-sonnet-4-6"
+    DEFAULT_VERTEX_MODEL = "claude-sonnet-4-6@default"
 
     if api_key and not use_vertex:
         os.environ["ANTHROPIC_API_KEY"] = api_key

components/runners/ambient-runner/tests/test_claude_auth.py

@@ -155,7 +155,7 @@ async def test_default_model_when_none_specified(self, monkeypatch):
         monkeypatch.delenv("ANTHROPIC_API_KEY", raising=False)
         ctx = _make_context(ANTHROPIC_API_KEY="sk-key")
         _, _, model = await setup_sdk_authentication(ctx)
-        assert model == "claude-sonnet-4-5"
+        assert model == "claude-sonnet-4-6"
         assert "@" not in model  # no Vertex date suffix for API key auth
 
     @pytest.mark.asyncio