fix: handle malformed function calls in vertex (#1987)

letta/llm_api/google_ai_client.py

@@ -122,8 +122,8 @@ class GoogleAIClient(LLMClientBase):
             for candidate in response_data["candidates"]:
                 content = candidate["content"]
 
-                if "role" not in content:
-                    # This means the response is malformed
+                if "role" not in content or not content["role"]:
+                    # This means the response is malformed like MALFORMED_FUNCTION_CALL
                     # NOTE: must be a ValueError to trigger a retry
                     raise ValueError(f"Error in response data from LLM: {response_data}")
                 role = content["role"]

letta/llm_api/google_vertex_client.py

@@ -110,7 +110,11 @@ class GoogleVertexClient(GoogleAIClient):
             for candidate in response.candidates:
                 content = candidate.content
 
-                role = content.role
+                if "role" not in content or not content["role"]:
+                    # This means the response is malformed like MALFORMED_FUNCTION_CALL
+                    # NOTE: must be a ValueError to trigger a retry
+                    raise ValueError(f"Error in response data from LLM: {response_data}")
+                role = content["role"]
                 assert role == "model", f"Unknown role in response: {role}"
 
                 parts = content.parts