feat: add AI reasoning summary generator with fallback

- Implement ReasoningSummarizer class for generating 2-3 sentence AI summaries
- Add fallback to statistical summary when AI generation fails
- Format reasoning logs for summary prompt with truncation
- Handle empty reasoning logs with default message
- Add comprehensive unit tests with async mocking

tests/unit/test_reasoning_summarizer.py

@@ -0,0 +1,80 @@
+import pytest
+from unittest.mock import AsyncMock, Mock
+from agent.reasoning_summarizer import ReasoningSummarizer
+
+
+class TestReasoningSummarizer:
+
+    @pytest.mark.asyncio
+    async def test_generate_summary_success(self):
+        """Test successful AI summary generation."""
+        # Mock AI model
+        mock_model = AsyncMock()
+        mock_model.ainvoke.return_value = Mock(
+            content="Analyzed AAPL earnings. Bought 10 shares based on positive guidance."
+        )
+
+        summarizer = ReasoningSummarizer(model=mock_model)
+
+        reasoning_log = [
+            {"role": "user", "content": "Analyze market"},
+            {"role": "assistant", "content": "Let me check AAPL"},
+            {"role": "tool", "name": "search", "content": "AAPL earnings positive"}
+        ]
+
+        summary = await summarizer.generate_summary(reasoning_log)
+
+        assert summary == "Analyzed AAPL earnings. Bought 10 shares based on positive guidance."
+        mock_model.ainvoke.assert_called_once()
+
+    @pytest.mark.asyncio
+    async def test_generate_summary_failure_fallback(self):
+        """Test fallback summary when AI generation fails."""
+        # Mock AI model that raises exception
+        mock_model = AsyncMock()
+        mock_model.ainvoke.side_effect = Exception("API error")
+
+        summarizer = ReasoningSummarizer(model=mock_model)
+
+        reasoning_log = [
+            {"role": "assistant", "content": "Let me search"},
+            {"role": "tool", "name": "search", "content": "Results"},
+            {"role": "tool", "name": "trade", "content": "Buy AAPL"},
+            {"role": "tool", "name": "trade", "content": "Sell MSFT"}
+        ]
+
+        summary = await summarizer.generate_summary(reasoning_log)
+
+        # Should return fallback with stats
+        assert "2 trades" in summary
+        assert "1 market searches" in summary
+
+    @pytest.mark.asyncio
+    async def test_format_reasoning_for_summary(self):
+        """Test condensing reasoning log for summary prompt."""
+        mock_model = AsyncMock()
+        summarizer = ReasoningSummarizer(model=mock_model)
+
+        reasoning_log = [
+            {"role": "user", "content": "System prompt here"},
+            {"role": "assistant", "content": "I will analyze AAPL"},
+            {"role": "tool", "name": "search", "content": "AAPL earnings data..."},
+            {"role": "assistant", "content": "Based on analysis, buying AAPL"}
+        ]
+
+        formatted = summarizer._format_reasoning_for_summary(reasoning_log)
+
+        # Should include key messages
+        assert "analyze AAPL" in formatted
+        assert "search" in formatted
+        assert "buying AAPL" in formatted
+
+    @pytest.mark.asyncio
+    async def test_empty_reasoning_log(self):
+        """Test handling empty reasoning log."""
+        mock_model = AsyncMock()
+        summarizer = ReasoningSummarizer(model=mock_model)
+
+        summary = await summarizer.generate_summary([])
+
+        assert summary == "No trading activity recorded."