1. Remove duplicate ToolResult definition in heartbeat package
- Import tools.ToolResult instead of local definition
- Add nil check for handler before execution
2. Fix SpawnTool to return AsyncResult and implement AsyncTool
- Add callback field and SetCallback method
- Return AsyncResult instead of NewToolResult
3. Add context cancellation support to SubagentManager
- Check ctx.Done() before and during task execution
- Set task status to "cancelled" on cancellation
- Call callback with result on completion
4. Fix data race window in CronTool.addJob
- Use Lock instead of RLock for channel/chatID access
- Ensure consistent snapshot during job creation
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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