debug: enable stdout/stderr for MCP services to diagnose parameter injection

MCP services were started with stdout/stderr redirected to DEVNULL, making
debug logs invisible. This prevented diagnosing why _current_position parameter
is not being received by buy() function.

Changed subprocess.Popen to redirect MCP service output to main process
stdout/stderr, allowing [DEBUG buy] logs to be visible in docker logs.

This will help identify whether:
1. _current_position is being sent by ContextInjector but not received
2. MCP HTTP transport filters underscore-prefixed parameters
3. Parameter serialization is failing

Related to negative cash bug where final position shows -$3,049.83 instead
of +$727.92 tracked by ContextInjector.

agent_tools/start_mcp_services.py

@@ -78,10 +78,11 @@ class MCPServiceManager:
             env['PYTHONPATH'] = str(Path.cwd())
 
             # Start service process (output goes to Docker logs)
+            # Enable stdout/stderr for debugging (previously sent to DEVNULL)
             process = subprocess.Popen(
                 [sys.executable, str(script_path)],
-                stdout=subprocess.DEVNULL,
-                stderr=subprocess.DEVNULL,
+                stdout=sys.stdout,  # Redirect to main process stdout
+                stderr=sys.stderr,  # Redirect to main process stderr
                 cwd=Path.cwd(),  # Use current working directory (/app)
                 env=env  # Pass environment with PYTHONPATH
             )

tests/unit/test_context_injector.py

@@ -2,6 +2,7 @@
 
 import pytest
 from agent.context_injector import ContextInjector
+from unittest.mock import Mock
 
 
 @pytest.fixture
@@ -22,27 +23,34 @@ class MockRequest:
         self.args = args or {}
 
 
+def create_mcp_result(position_dict):
+    """Create a mock MCP CallToolResult object matching production behavior."""
+    result = Mock()
+    result.structuredContent = position_dict
+    return result
+
+
 async def mock_handler_success(request):
-    """Mock handler that returns a successful position update."""
+    """Mock handler that returns a successful position update as MCP CallToolResult."""
     # Simulate a successful trade returning updated position
     if request.name == "sell":
-        return {
+        return create_mcp_result({
             "CASH": 1100.0,
             "AAPL": 7,
             "MSFT": 5
-        }
+        })
     elif request.name == "buy":
-        return {
+        return create_mcp_result({
             "CASH": 50.0,
             "AAPL": 7,
             "MSFT": 12
-        }
-    return {}
+        })
+    return create_mcp_result({})
 
 
 async def mock_handler_error(request):
-    """Mock handler that returns an error."""
-    return {"error": "Insufficient cash"}
+    """Mock handler that returns an error as MCP CallToolResult."""
+    return create_mcp_result({"error": "Insufficient cash"})
 
 
 @pytest.mark.asyncio
@@ -68,17 +76,17 @@ async def test_context_injector_injects_parameters(injector):
     """Test that context parameters are injected into buy/sell requests."""
     request = MockRequest("buy", {"symbol": "AAPL", "amount": 10})
 
-    # Mock handler that just returns the request args
+    # Mock handler that returns MCP result containing the request args
     async def handler(req):
-        return req.args
+        return create_mcp_result(req.args)
 
     result = await injector(request, handler)
 
-    # Verify context was injected
-    assert result["signature"] == "test-model"
-    assert result["today_date"] == "2025-01-15"
-    assert result["job_id"] == "test-job-123"
-    assert result["trading_day_id"] == 1
+    # Verify context was injected (result is MCP CallToolResult object)
+    assert result.structuredContent["signature"] == "test-model"
+    assert result.structuredContent["today_date"] == "2025-01-15"
+    assert result.structuredContent["job_id"] == "test-job-123"
+    assert result.structuredContent["trading_day_id"] == 1
 
 
 @pytest.mark.asyncio
@@ -132,7 +140,7 @@ async def test_context_injector_does_not_update_position_on_error(injector):
 
     # Verify position was NOT updated
     assert injector._current_position == original_position
-    assert "error" in result
+    assert "error" in result.structuredContent
 
 
 @pytest.mark.asyncio
@@ -146,7 +154,7 @@ async def test_context_injector_does_not_inject_position_for_non_trade_tools(inj
 
     async def verify_no_injection_handler(req):
         assert "_current_position" not in req.args
-        return {"results": []}
+        return create_mcp_result({"results": []})
 
     await injector(request, verify_no_injection_handler)
 
@@ -164,7 +172,7 @@ async def test_context_injector_full_trading_session_simulation(injector):
     async def handler1(req):
         # First trade should NOT have injected position
         assert req.args.get("_current_position") is None
-        return {"CASH": 1100.0, "AAPL": 7}
+        return create_mcp_result({"CASH": 1100.0, "AAPL": 7})
 
     result1 = await injector(request1, handler1)
     assert injector._current_position == {"CASH": 1100.0, "AAPL": 7}
@@ -176,7 +184,7 @@ async def test_context_injector_full_trading_session_simulation(injector):
         # Second trade SHOULD have injected position from trade 1
         assert req.args["_current_position"]["CASH"] == 1100.0
         assert req.args["_current_position"]["AAPL"] == 7
-        return {"CASH": 50.0, "AAPL": 7, "MSFT": 7}
+        return create_mcp_result({"CASH": 50.0, "AAPL": 7, "MSFT": 7})
 
     result2 = await injector(request2, handler2)
     assert injector._current_position == {"CASH": 50.0, "AAPL": 7, "MSFT": 7}
@@ -185,7 +193,7 @@ async def test_context_injector_full_trading_session_simulation(injector):
     request3 = MockRequest("buy", {"symbol": "GOOGL", "amount": 100})
 
     async def handler3(req):
-        return {"error": "Insufficient cash", "cash_available": 50.0}
+        return create_mcp_result({"error": "Insufficient cash", "cash_available": 50.0})
 
     result3 = await injector(request3, handler3)
     # Position should remain unchanged after failed trade