Create Durable Plan

Overview

Write a durable plan pack in the repo. Target plans/<YYYY-MM-DD-slug>/. A later coding agent with no chat history must know what to do, where, how, in what order, which invariants to preserve, when to stop, and how to prove a phase is done.

This skill researches and writes plan files. It does not implement product work unless the user explicitly asks after the pack exists.

Output pack