Add --cwd <path> / --cwd=<path> support so sandboxed subagents running outside the project root can target a specific directory. Invalid paths return a clear error. Tests ported to tests/state.test.cjs (the old monolithic test file was split into domain files on main). Closes #622 Co-Authored-By: Colin Johnson <colin@solvely.net> Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>