feat: add conversation history tracking to BaseAgent

- Add conversation_history instance variable to BaseAgent.__init__
- Create _capture_message() method to capture messages with timestamps
- Create get_conversation_history() method to retrieve conversation
- Create clear_conversation_history() method to reset history
- Modify run_trading_session() to capture user prompts and AI responses
- Add comprehensive unit tests for conversation tracking
- Fix datetime deprecation warning by using timezone-aware datetime

All tests pass successfully.

tests/unit/test_base_agent_conversation.py

@@ -0,0 +1,95 @@
+"""Tests for BaseAgent conversation history tracking."""
+
+import pytest
+from agent.base_agent.base_agent import BaseAgent
+
+
+def test_conversation_history_initialized_empty():
+    """Conversation history should start empty."""
+    agent = BaseAgent(
+        signature="test-agent",
+        basemodel="test-model"
+    )
+    assert agent.conversation_history == []
+    assert agent.get_conversation_history() == []
+
+
+def test_capture_message_user():
+    """Should capture user message."""
+    agent = BaseAgent(
+        signature="test-agent",
+        basemodel="test-model"
+    )
+    agent._capture_message("user", "Test prompt")
+
+    history = agent.get_conversation_history()
+    assert len(history) == 1
+    assert history[0]["role"] == "user"
+    assert history[0]["content"] == "Test prompt"
+    assert "timestamp" in history[0]
+
+
+def test_capture_message_assistant():
+    """Should capture assistant message."""
+    agent = BaseAgent(
+        signature="test-agent",
+        basemodel="test-model"
+    )
+    agent._capture_message("assistant", "Test response")
+
+    history = agent.get_conversation_history()
+    assert len(history) == 1
+    assert history[0]["role"] == "assistant"
+    assert history[0]["content"] == "Test response"
+
+
+def test_capture_message_tool():
+    """Should capture tool message with tool info."""
+    agent = BaseAgent(
+        signature="test-agent",
+        basemodel="test-model"
+    )
+    agent._capture_message(
+        "tool",
+        "Tool result",
+        tool_name="get_price",
+        tool_input='{"symbol": "AAPL"}'
+    )
+
+    history = agent.get_conversation_history()
+    assert len(history) == 1
+    assert history[0]["role"] == "tool"
+    assert history[0]["tool_name"] == "get_price"
+    assert history[0]["tool_input"] == '{"symbol": "AAPL"}'
+
+
+def test_clear_conversation_history():
+    """Should clear conversation history."""
+    agent = BaseAgent(
+        signature="test-agent",
+        basemodel="test-model"
+    )
+    agent._capture_message("user", "Test")
+    assert len(agent.get_conversation_history()) == 1
+
+    agent.clear_conversation_history()
+    assert len(agent.get_conversation_history()) == 0
+
+
+def test_get_conversation_history_returns_copy():
+    """Should return a copy to prevent external modification."""
+    agent = BaseAgent(
+        signature="test-agent",
+        basemodel="test-model"
+    )
+    agent._capture_message("user", "Test")
+
+    history1 = agent.get_conversation_history()
+    history2 = agent.get_conversation_history()
+
+    # Modify one copy
+    history1.append({"role": "user", "content": "Extra"})
+
+    # Other copy should be unaffected
+    assert len(history2) == 1
+    assert len(agent.conversation_history) == 1