Adds --only N flag to /gsd:autonomous that restricts execution to a
single phase, enabling safe parallel execution across terminals:
Terminal 1: /gsd:autonomous --only 16
Terminal 2: /gsd:autonomous --only 17
Terminal 3: /gsd:autonomous --only 18
Changes:
- Step 1: Parse --only N alongside --from N (also sets FROM_PHASE)
- Step 2: Filter phase list to exact match when --only active
- Step 4: Skip iteration — single phase does not loop
- Step 5: Skip lifecycle — audit/complete/cleanup only for full runs
- Step 6: Resume message uses --only when active
- Success criteria updated with --only N requirements
Parallel safety: each phase operates in its own .planning/phases/NN-*
directory. ROADMAP.md and STATE.md are read-only during phase execution.
Closes#1383
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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