feat: follow-up message interrupt (like vanilla Claude Code)

[Fr4nzz]

Summary

• When a user sends a follow-up message while Claude is processing, the bot interrupts the current task and immediately processes the follow-up in the same session
• Uses the SDK's client.interrupt() control protocol (equivalent to Ctrl+C)
• If graceful interrupt doesn't stop within 3 seconds, falls back to killing the subprocess
• Session history is preserved across interrupts — Claude remembers everything
• Adds /stop command for manually cancelling tasks
• Enables concurrent_updates(True) so follow-up messages are handled in parallel

How it works

1. User sends message A → Claude starts processing
2. User sends message B while Claude is working
3. Bot sends interrupt() signal to Claude (like Ctrl+C)
4. Claude stops, session ID is preserved
5. Bot immediately sends message B as a continuation of the same session
6. Claude sees full conversation history + message B

Test plan

• Send a long task, then send a follow-up while processing
• Verify 📨 Interrupting... appears and the follow-up is processed
• Verify /stop cancels a running task
• Verify session continues after interrupt (Claude remembers context)
• Verify normal sequential messages still work when no task is running

🤖 Generated with Claude Code