When the repo is in a broken state (wrong branch, detached HEAD, deleted
worktree), gt handoff would fail with "cannot detect town root" error.
This is exactly when handoff is most needed - to recover and hand off
to a fresh session.
Changes:
- detectTownRootFromCwd() now falls back to GT_TOWN_ROOT and GT_ROOT
environment variables when cwd-based detection fails
- buildRestartCommand() now propagates GT_ROOT to ensure subsequent
handoffs can also use the fallback
- Added tests for the fallback behavior
Fixes gt-x2q81.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
