fix(llm): collapse multimodal content with the shared helper (#7527)

For response_model calls the messages are flattened into one prompt for
InternalInstructor with an f-string, so a multimodal content list reached the
model as its Python repr. AGENTS.md's "Message Content" section says never to
str() the content; use message_content_text() instead.

lib/crewai/src/crewai/llm.py

@@ -1263,6 +1263,7 @@ class LLM(BaseLLM):
         """
         if response_model and self.is_litellm:
             from crewai.hooks.llm_hooks import model_call_hooks_dispatched
+            from crewai.utilities.agent_utils import message_content_text
             from crewai.utilities.internal_instructor import InternalInstructor
 
             messages = params.get("messages", [])
@@ -1270,7 +1271,8 @@ class LLM(BaseLLM):
                 raise ValueError("Messages are required when using response_model")
 
             combined_content = "\n\n".join(
-                f"{msg['role'].upper()}: {msg['content']}" for msg in messages
+                f"{msg['role'].upper()}: {message_content_text(msg)}"
+                for msg in messages
             )
 
             instructor_instance = InternalInstructor(
@@ -1420,6 +1422,7 @@ class LLM(BaseLLM):
         """
         if response_model and self.is_litellm:
             from crewai.hooks.llm_hooks import model_call_hooks_dispatched
+            from crewai.utilities.agent_utils import message_content_text
             from crewai.utilities.internal_instructor import InternalInstructor
 
             messages = params.get("messages", [])
@@ -1427,7 +1430,8 @@ class LLM(BaseLLM):
                 raise ValueError("Messages are required when using response_model")
 
             combined_content = "\n\n".join(
-                f"{msg['role'].upper()}: {msg['content']}" for msg in messages
+                f"{msg['role'].upper()}: {message_content_text(msg)}"
+                for msg in messages
             )
 
             instructor_instance = InternalInstructor(

lib/crewai/tests/llms/test_structured_output_multimodal.py

@@ -0,0 +1,62 @@
+"""Structured output must collapse multimodal content with the shared helper."""
+
+from unittest.mock import patch
+
+import pytest
+from pydantic import BaseModel
+
+from crewai.llm import LLM
+
+
+class Answer(BaseModel):
+    text: str
+
+
+MULTIMODAL = [
+    {
+        "role": "user",
+        "content": [
+            {"type": "text", "text": "What is in this image?"},
+            {"type": "image_url", "image_url": {"url": "http://example.com/x.png"}},
+        ],
+    }
+]
+
+
+def _stub_llm():
+    """An LLM with the instructor call captured, no network involved."""
+    llm = object.__new__(LLM)
+    llm.is_litellm = True
+    llm._handle_emit_call_events = lambda **kwargs: None
+    captured: dict[str, str] = {}
+
+    class FakeInstructor:
+        def __init__(self, *, content, model, llm):
+            captured["content"] = content
+
+        def to_pydantic(self):
+            return Answer(text="ok")
+
+    patcher = patch(
+        "crewai.utilities.internal_instructor.InternalInstructor", FakeInstructor
+    )
+    return llm, captured, patcher
+
+
+def test_sync_structured_output_collapses_multimodal_content():
+    llm, captured, patcher = _stub_llm()
+    with patcher:
+        llm._handle_non_streaming_response(
+            params={"messages": MULTIMODAL}, response_model=Answer
+        )
+    assert captured["content"] == "USER: What is in this image?"
+
+
+@pytest.mark.asyncio
+async def test_async_structured_output_collapses_multimodal_content():
+    llm, captured, patcher = _stub_llm()
+    with patcher:
+        await llm._ahandle_non_streaming_response(
+            params={"messages": MULTIMODAL}, response_model=Answer
+        )
+    assert captured["content"] == "USER: What is in this image?"