* fix(tmux): send Ctrl+C before kill-pane and respawn-pane to prevent orphaned processes
* fix(tmux-subagent): prevent premature pane closure with stability detection
Implements stability detection pattern from background-agent to prevent
tmux panes from closing while agents are still working (issue #1330).
Problem: Session status 'idle' doesn't mean 'finished' - agent may still
be thinking/reasoning. Previous code closed panes immediately on idle.
Solution:
- Require MIN_STABILITY_TIME_MS (10s) before stability detection activates
- Track message count changes to detect ongoing activity
- Require STABLE_POLLS_REQUIRED (3) consecutive polls with same message count
- Double-check session status before closing
Changes:
- types.ts: Add lastMessageCount and stableIdlePolls to TrackedSession
- manager.ts: Implement stability detection in pollSessions()
- manager.test.ts: Add 4 tests for stability detection behavior
* test(tmux-subagent): improve stability detection tests to properly verify age gate
- First test now sets session age >10s and verifies 3 polls don't close
- Last test now does 5 polls to prove age gate prevents closure
- Added comments explaining what each poll does
- Account for tmux pane dividers (1 char) in all size calculations
- Reduce MIN_PANE_WIDTH from 53 to 52 to fit 2 columns in standard terminals
- Fix enforceMainPaneWidth to use (windowWidth - divider) / 2
- Add virtual mainPane handling for close-spawn eviction loop
- Add comprehensive decision-engine tests (23 test cases)
