fix: use SessionManager methods for pending tool call state management

- Replace direct session service access with SessionManager's get_state_value and set_state_value methods
- Simplifies state management by using higher-level abstraction
- Fixes issue #25 by using proper SessionManager API for state updates
- Maintains same functionality with cleaner implementation

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: mefogle

typescript-sdk/integrations/adk-middleware/CHANGELOG.md

@@ -15,11 +15,13 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - **FIXED**: Race condition in tool result processing causing "No pending tool calls found" warnings
 - **FIXED**: Tool call removal now happens after pending check to prevent race conditions
 - **IMPROVED**: Better handling of empty tool result content with graceful JSON parsing fallback
+- **FIXED**: Pending tool call state management now uses SessionManager methods (issue #25)
 
 ### Enhanced
 - **LOGGING**: Added debug logging for tool result processing to aid in troubleshooting
 - **ARCHITECTURE**: Consolidated agent copying logic to avoid creating multiple unnecessary copies
 - **CLEANUP**: Removed unused toolset parameter from `_run_adk_in_background` method
+- **REFACTOR**: Replaced direct session service access with SessionManager state management methods for pending tool calls
 
 ## [0.4.1] - 2025-07-13