Plan-as-Agreement — Fit-for-Purpose Implementation Plans

Every modern agentic coding harness — Claude Code (~/.claude/plans/), Cursor Plan Mode (.cursor/plans/), Cline's "Plan → Preview → Apply" — persists a markdown plan as the gate between intent and execution. The plan.md is the highest-leverage single document in an agentic session: a tight plan reviewed in 2 minutes saves 20–60 minutes of wrong-turn execution downstream.

These harnesses do not, however, shape the plan for the task. A 23-line comment-trim PR receives the same scaffold as a new authentication subsystem. This skill closes that gap: it selects from a library of 16 named formats (and supports 2–3 format hybrids), renders one plan.md with a one-line banner explaining the choice, and accepts plain-English overrides like "use exact-diff and stats-driven".

It complements the IDE harness — the harness owns research → clarify → approve → execute; this skill owns the shape of the artifact the harness writes.