Tool Use Concurrency Error Handler

What: New error handler for API 400 errors caused by tool use concurrency issues

How to recover: When you encounter this error, the system will display:

API Error: 400 due to tool use concurrency issues. Run /rewind to recover the conversation.

Details:

• Detects when tool_use IDs are found without immediately following tool_result blocks
• Provides clear recovery instructions using the existing /rewind command
• The /rewind command restores both code state and conversation to a previous checkpoint
• Evidence: Error handler at bk1() at line 385221

Why this matters: Provides users with actionable recovery steps instead of a generic API error message when tool execution gets out of sync.