When multiple agents start simultaneously (e.g., `gt up`), each runs
`gt nudge deacon session-started` in their SessionStart hook. These
nudges arrive concurrently and can interleave in the tmux input buffer,
causing:
1. Text from one nudge mixing with another
2. Enter keys not properly submitting messages
3. Garbled input requiring manual intervention
This fix adds per-session mutex serialization to NudgeSession() and
NudgePane(). Concurrent nudges to the same session now queue and
execute one at a time.
## Root Cause
The NudgeSession pattern sends text, waits 500ms, sends Escape, waits
100ms, then sends Enter. When multiple nudges arrive within this ~800ms
window, their send-keys commands interleave, corrupting the input.
## Alternatives Considered
1. **Delay deacon nudges** - Add sleep before nudge in SessionStart
- Simplest (one-line change)
- But: doesn't prevent concurrent nudges from multiple agents
2. **Debounce session-started** - Deacon ignores rapid-fire nudges
- Medium complexity
- But: only helps session-started, not other nudge types
3. **File-based signaling** - Replace tmux nudges with file watches
- Avoids tmux input issues entirely
- But: significant architectural change
4. **File upstream bug** - Report to Claude Code team
- SessionStart hooks fire async and can interleave
- But: fix timeline unknown, need robustness now
## Tradeoffs
- Concurrent nudges to same session now queue (adds latency)
- Memory: one mutex per unique session name (bounded, acceptable)
- Does not fix Claude Code's underlying async hook behavior
## Testing
- Build passes
- All tmux package tests pass
- Manual testing: started deacon + multiple witnesses concurrently,
nudges processed correctly without garbled input
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
e344e77921