rota-plan — Implementation Plan as Artifact

Write a plan the user signs off on before /rota-work runs. Keyed by a backlog item (#42 on the issue backend; file backend B07, F03, T11 keep the M01-B07 form) or a milestone slice, M01-S01. A milestone is never required. Issue backend: an item plan is a note on the item's issue, a slice plan lives on the milestone's tracking issue. File backend: .rota/plans/<key>.md.

Copy this checklist and track your progress:

- [ ] Step 1 — Resolve target
- [ ] Step 2 — Load context, once
- [ ] Step 3 — One proposal
- [ ] Step 4 — Write
- [ ] Step 5 — Report

Step 1 — Resolve target

• Item (#42, B07, …): item mode; the key is the ref as given (M01-B07 is equally valid for a milestone-tagged item).
• Milestone (M01): slice mode; the next slice number is minted.
• Free-form: find the item with rota backlog / rota item show; ask only if still ambiguous.