test(fallback): classify authentication exception messages

nanobot/providers/fallback_provider.py

@@ -623,6 +623,8 @@ class FallbackProvider(LLMProvider):
             raise
         except Exception as exc:
             error_name = type(exc).__name__.lower()
+            detail = str(exc).strip() or type(exc).__name__
+            detail_lower = detail.lower()
             error_kind: str | None = None
             error_should_retry: bool | None = None
             if isinstance(exc, (httpx.TimeoutException, asyncio.TimeoutError)):
@@ -634,7 +636,7 @@ class FallbackProvider(LLMProvider):
             elif any(
                 token in error_name
                 for token in ("auth", "credential", "permissiondenied", "unauthor")
-            ):
+            ) or any(token in detail_lower for token in _AUTHENTICATION_ERROR_TOKENS):
                 error_kind = "authentication"
             elif "ratelimit" in error_name or "throttl" in error_name:
                 error_kind = "rate_limit"
@@ -652,7 +654,6 @@ class FallbackProvider(LLMProvider):
             except (TypeError, ValueError):
                 error_status_code = None
 
-            detail = str(exc).strip() or type(exc).__name__
             return LLMResponse(
                 content=f"Error calling LLM: {detail}",
                 finish_reason="error",

tests/agent/test_runner_fallback.py

@@ -423,6 +423,19 @@ class TestFallbackWhenPrimaryRaises:
         assert result.finish_reason == "stop"
         factory.assert_called_once_with(_fallback("fallback-a"))
 
+    @pytest.mark.asyncio
+    async def test_authentication_exception_message_is_classified(self) -> None:
+        primary = _RaisingProvider("primary")
+
+        response, exception = await FallbackProvider._call_provider(
+            lambda provider, kwargs: provider.chat(**kwargs),
+            primary,
+            {},
+        )
+
+        assert exception is primary._exc
+        assert response.error_kind == "authentication"
+
     @pytest.mark.parametrize(
         "exc",
         [