fix: classify OpenRouter 'no endpoints found that support tool use' 404 as model_not_found with fallback

agent/error_classifier.py

@@ -279,6 +279,15 @@ def is_auth(self) -> bool:
     "no such model",
     "unknown model",
     "unsupported model",
+    # OpenRouter returns 404 with this message when none of the candidate
+    # endpoints for the selected model support tool/function calling.
+    # Classifying this as model_not_found triggers fallback to a different
+    # model or provider that does support tools.  Without this entry the
+    # pattern falls through to ``unknown`` with ``retryable=True``, the
+    # retry loop burns all attempts on the same deterministic rejection,
+    # and the error surfaces as a confusing "model not found" message
+    # instead of automatically failing over.  See PR #58446.
+    "no endpoints found that support tool use",
 ]
 
 # Request-validation patterns — the request is malformed and will fail

tests/agent/test_error_classifier.py

@@ -516,6 +516,21 @@ def test_404_model_not_found(self):
         assert result.should_fallback is True
         assert result.retryable is False
 
+    def test_404_openrouter_tool_use_not_supported(self):
+        # OpenRouter returns 404 with this message when none of the
+        # candidate endpoints for the selected model support tool/function
+        # calling.  Classify as model_not_found so the agent fast-fallbacks
+        # to a model/provider that does support tools.
+        e = MockAPIError(
+            "No endpoints found that support tool use. "
+            "Try disabling \"browser_back\".",
+            status_code=404,
+        )
+        result = classify_api_error(e)
+        assert result.reason == FailoverReason.model_not_found
+        assert result.should_fallback is True
+        assert result.retryable is False
+
     def test_404_generic(self):
         # Generic 404 with no "model not found" signal — common for local
         # llama.cpp/Ollama/vLLM endpoints with slightly wrong paths.  Treat