feat: run milestone mapping on mgw:milestone completion and mgw:project extend

[snipcodeit]

Summary

After milestone completes, verify next milestone has proper GSD linkage. If next milestone has no gsd_milestone_id, prompt user to run gsd:new-milestone. In extend mode, run mapping after write_project_json.

Post-Completion Logic

• After advancing active_gsd_milestone
• Check next milestone's gsd_milestone_id
• If null: "Next milestone 'X' has no GSD milestone linked. Run /gsd:new-milestone then /mgw:project to link."
• If set: verify .planning/ROADMAP.md matches expected milestone

Files

• commands/milestone.md — add mapping verification in post_loop step
• commands/project.md — add mapping verification after write_project_json in extend mode

GSD Route

gsd:quick

Depends On

• C1 (active_gsd_milestone)
• C3 (maps-to links exist to verify)

[snipcodeit]

MGW execution-complete · 2026-03-01T00:00:00Z
Milestone: v3 — Multi-Milestone Tracking | Phase 26: Milestone Completion Mapping

Implementation Complete

Implemented in commit f1b4830 on branch feat/mgw-gsd-architecture-repair.

Added milestone mapping verification to commands/milestone.md (post_loop step): when a milestone completes, checks if the next milestone's gsd_milestone_id is set. If unlinked, warns and optionally runs milestone_mapper to create the mapping. Also extended commands/project.md (extend mode) with the same linkage verification block to catch unlinked milestones during project extension.

Part of PR #102.