fix: after_llm_call hooks no longer break native tool execution (#6531)

* fix: don't clobber native tool-call responses in after-LLM hooks

Registering any `after_llm_call` hook broke native tool execution: the
executor invokes `_setup_after_llm_call_hooks` on the intermediate
response that carries the model's tool calls, the non-str payload was
stringified for the response-rewrite pass, and the executor then treated
that string as a final answer instead of executing the tools. Structured
payloads (neither `str` nor `BaseModel`) now pass through untouched,
mirroring the isinstance guard `_invoke_after_llm_call_hooks` already
applies on the direct-call path; hooks still fire on the follow-up
textual response.

Fixes #6529

* style: shorten the tool-call guard comment

lib/crewai/src/crewai/utilities/agent_utils.py

@@ -1751,6 +1751,12 @@ def _setup_after_llm_call_hooks(
     if executor_context and executor_context.after_llm_call_hooks:
         from crewai.hooks.llm_hooks import LLMCallHookContext
 
+        # Don't stringify structured tool-call payloads: the executor would
+        # treat the result as a final answer and skip tool execution (#6529).
+        # Hooks still run on the follow-up textual response.
+        if not isinstance(answer, (str, BaseModel)):
+            return answer
+
         original_messages = executor_context.messages
 
         if isinstance(answer, BaseModel):

lib/crewai/tests/hooks/test_llm_hooks.py

@@ -272,6 +272,40 @@ class TestLLMHooksIntegration:
 
         assert result == "Original [hook1] [hook2]"
 
+    def test_after_hooks_do_not_clobber_native_tool_call_responses(
+        self, mock_executor
+    ):
+        """A registered after hook must not break native tool execution.
+
+        Regression for crewAIInc/crewAI#6529: `_setup_after_llm_call_hooks`
+        stringified structured tool-call payloads, so the executor treated the
+        raw tool call as the final answer and never executed the tool. Non-str,
+        non-BaseModel responses now pass through untouched; hooks still fire on
+        textual responses.
+        """
+        from crewai.utilities.agent_utils import _setup_after_llm_call_hooks
+
+        observed = []
+
+        def observer(context):
+            observed.append(context.response)
+            return None
+
+        register_after_llm_call_hook(observer)
+        mock_executor.after_llm_call_hooks = get_after_llm_call_hooks()
+
+        tool_calls = [Mock()]  # structured native tool-call payload
+        result = _setup_after_llm_call_hooks(
+            mock_executor, tool_calls, printer=Mock(), verbose=False
+        )
+        assert result is tool_calls
+
+        text = _setup_after_llm_call_hooks(
+            mock_executor, "final answer", printer=Mock(), verbose=False
+        )
+        assert text == "final answer"
+        assert observed == ["final answer"]
+
     def test_unregister_before_hook(self):
         """Test that before hooks can be unregistered."""
         def test_hook(context):