plan-milestone

name	plan-milestone
description	Scaffolds a milestone plan against CLAUDE.md and DESIGN.md, prompting for milestone-specific details before producing the plan.
disable-model-invocation	true
argument-hint	[milestone-number]

Plan Milestone $ARGUMENTS

1. Read CLAUDE.md's "## Current focus" section to confirm the currently/previously recorded milestone number. If $ARGUMENTS isn't exactly one more than the last completed milestone (or doesn't otherwise make sense — e.g., re-planning the same milestone), stop and flag the discrepancy before proceeding.

2. Ask the user for milestone-specific details: what this milestone covers, why it comes next, and any constraints, deviations from DESIGN.md, or open questions they already have in mind. Wait for their answer — do not guess or proceed on assumptions.

Once they respond:

3. Re-read CLAUDE.md and DESIGN.md fresh. For prior-milestone detail, the single log is MILESTONES.md (CLAUDE.md's "## Completed milestones" carries only a one-line index); the forward roadmap is DESIGN.md §15 and deferred/remaining decisions are DESIGN.md §14.

4. Confirm this milestone's scope against DESIGN.md §15 (roadmap) and §14 (decisions remaining), and CLAUDE.md's "out of scope for now" list; confirm it isn't already done per the MILESTONES.md log; flag if the user's details conflict with any of these.

5. Propose a concrete plan: files to create/modify (name the R wrappers, C++ cores, tests, and docs), the order of implementation, and testable acceptance criteria in the same style as M1's (see MILESTONES.md).

6. For any milestone touching a C++ core, the plan must include: a Rcpp::compileAttributes() regeneration step, a numerical-regression test vs. a reference implementation on sim_dyad (Invariant 5), and — for efficiency work — a bench/ before/after timing step with a measured target.

7. Flag any design ambiguity the brief doesn't resolve — do not invent a resolution; if it's a design decision, it belongs in DESIGN.md, so ask.

8. Do not write any code. This is planning only; implementation happens via /implement-milestone afterward.

9. Once the user explicitly approves the plan (branch → PR workflow; milestone work never lands directly on main): a. Create the milestone's feature branch off an up-to-date main (e.g. git switch main && git pull && git switch -c m$ARGUMENTS-<short-slug>). All milestone work — the planning commit and implementation — lands on this branch; main is updated only by merging a reviewed PR once CI is green (see /implement-milestone). b. On the branch, update CLAUDE.md's "## Current focus" section to make Milestone $ARGUMENTS active (with its acceptance criteria), and commit that change on its own (not bundled with any implementation commit). Commit locally only — do not push the branch or open the PR until the user asks (respects CLAUDE.md's "push only when asked" cadence).