fix: extract position dict from CallToolResult.structuredContent

Fix negative cash bug where ContextInjector._current_position never updated.

Root cause: MCP tools return mcp.types.CallToolResult objects, not plain
dicts. The isinstance(result, dict) check always failed, preventing
_current_position from accumulating trades within a session.

This caused all trades to calculate from initial $10,000 position instead
of previous trade's ending position, resulting in negative cash balances
when total purchases exceeded $10,000.

Solution: Extract position dict from CallToolResult.structuredContent field
before validating. Maintains backward compatibility by handling both
CallToolResult objects (production) and plain dicts (unit tests).

Impact:
- Fixes negative cash positions (e.g., -$8,768.68 after 11 trades)
- Enables proper intra-day position tracking
- Validates sufficient cash before each trade based on cumulative position
- Trade tool responses now properly accumulate all holdings

Testing:
- All existing unit tests pass (handle plain dict results)
- Production logs confirm structuredContent extraction works
- Debug logging shows _current_position now updates after each trade

agent/context_injector.py

@@ -91,15 +91,25 @@ class ContextInjector:
             # Debug: Log result type and structure
             print(f"[DEBUG ContextInjector] Trade result type: {type(result)}")
             print(f"[DEBUG ContextInjector] Trade result: {result}")
-            print(f"[DEBUG ContextInjector] isinstance(result, dict): {isinstance(result, dict)}")
 
-            # Check if result is a valid position dict (not an error)
-            if isinstance(result, dict) and "error" not in result and "CASH" in result:
+            # Extract position dict from MCP result
+            # MCP tools return CallToolResult objects with structuredContent field
+            position_dict = None
+            if hasattr(result, 'structuredContent') and result.structuredContent:
+                position_dict = result.structuredContent
+                print(f"[DEBUG ContextInjector] Extracted from structuredContent: {position_dict}")
+            elif isinstance(result, dict):
+                position_dict = result
+                print(f"[DEBUG ContextInjector] Using result as dict: {position_dict}")
+
+            # Check if position dict is valid (not an error) and update state
+            if position_dict and "error" not in position_dict and "CASH" in position_dict:
                 # Update our tracked position with the new state
-                self._current_position = result.copy()
+                self._current_position = position_dict.copy()
                 print(f"[DEBUG ContextInjector] Updated _current_position: {self._current_position}")
             else:
                 print(f"[DEBUG ContextInjector] Did NOT update _current_position - check failed")
+                print(f"[DEBUG ContextInjector] position_dict: {position_dict}")
                 print(f"[DEBUG ContextInjector] _current_position remains: {self._current_position}")
 
         return result