- Steps 1-7: Validate, parse, spawn planner (existing flow)
- Step 8: Spawn gsd-plan-checker with verification_context
- Step 9: Handle checker return (passed | issues)
- Step 10: Revision loop (max 3 iterations)
- Step 11: Present final status with verification outcome
User sees ping-pong between planner and checker in main context.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>