feat: expose messages to TaskOutput and LiteAgentOutputs (#3880)

* feat: add messages to task and agent outputs

- Introduced a new  field in  and  to capture messages from the last task execution.
- Updated the  class to store the last messages and provide a property for easy access.
- Enhanced the  and  classes to include messages in their outputs.
- Added tests to ensure that messages are correctly included in task outputs and agent outputs during execution.

* using typing_extensions for 3.10 compatability

* feat: add last_messages attribute to agent for improved task tracking

- Introduced a new `last_messages` attribute in the agent class to store messages from the last task execution.
- Updated the `Crew` class to handle the new messages attribute in task outputs.
- Enhanced existing tests to ensure that the `last_messages` attribute is correctly initialized and utilized across various guardrail scenarios.

* fix: add messages field to TaskOutput in tests for consistency

- Updated multiple test cases to include the new `messages` field in the `TaskOutput` instances.
- Ensured that all relevant tests reflect the latest changes in the TaskOutput structure, maintaining consistency across the test suite.
- This change aligns with the recent addition of the `last_messages` attribute in the agent class for improved task tracking.

* feat: preserve messages in task outputs during replay

- Added functionality to the Crew class to store and retrieve messages in task outputs.
- Enhanced the replay mechanism to ensure that messages from stored task outputs are preserved and accessible.
- Introduced a new test case to verify that messages are correctly stored and replayed, ensuring consistency in task execution and output handling.
- This change improves the overall tracking and context retention of task interactions within the CrewAI framework.

* fix original test, prev was debugging

lib/crewai/tests/test_task.py

@@ -162,6 +162,7 @@ def test_task_callback_returns_task_output():
             "name": task.name or task.description,
             "expected_output": "Bullet point list of 5 interesting ideas.",
             "output_format": OutputFormat.RAW,
+            "messages": [],
         }
         assert output_dict == expected_output
 
@@ -1680,3 +1681,44 @@ def test_task_copy_with_list_context():
     assert isinstance(copied_task2.context, list)
     assert len(copied_task2.context) == 1
     assert copied_task2.context[0] is task1
+
+
+@pytest.mark.vcr(filter_headers=["authorization"])
+def test_task_output_includes_messages():
+    """Test that TaskOutput includes messages from agent execution."""
+    researcher = Agent(
+        role="Researcher",
+        goal="Make the best research and analysis on content about AI and AI agents",
+        backstory="You're an expert researcher, specialized in technology, software engineering, AI and startups. You work as a freelancer and is now working on doing research and analysis for a new customer.",
+        allow_delegation=False,
+    )
+
+    task1 = Task(
+        description="Give me a list of 3 interesting ideas about AI.",
+        expected_output="Bullet point list of 3 ideas.",
+        agent=researcher,
+    )
+
+    task2 = Task(
+        description="Summarize the ideas from the previous task.",
+        expected_output="A summary of the ideas.",
+        agent=researcher,
+    )
+
+    crew = Crew(agents=[researcher], tasks=[task1, task2], process=Process.sequential)
+    result = crew.kickoff()
+
+    # Verify both tasks have messages
+    assert len(result.tasks_output) == 2
+
+    # Check first task output has messages
+    task1_output = result.tasks_output[0]
+    assert hasattr(task1_output, "messages")
+    assert isinstance(task1_output.messages, list)
+    assert len(task1_output.messages) > 0
+
+    # Check second task output has messages
+    task2_output = result.tasks_output[1]
+    assert hasattr(task2_output, "messages")
+    assert isinstance(task2_output.messages, list)
+    assert len(task2_output.messages) > 0