checkpoint-handofflisted

# Checkpoint Handoff ## The failure mode this fixes Long projects outlive context windows. The session that planned the work is never the session that finishes it — compaction, restarts, and tomorrow all guarantee that. And when the boundary hits without preparation, the next session starts by *reconstructing* instead of working: re-deriving the plan, re-discovering which tasks were done, re-learning the constraint the user stated forcefully forty turns ago, and — worst — confidently redoing or undoing finished work because nothing recorded that it was finished. Conversation memory is the wrong place for project state. Summaries compress; the exact rule ("never X, always Y"), the precise task ordering, and the "we already tried that, it fails because Z" knowledge are exactly what compression loses. The fix is mechanical: before the boundary, the state gets written to durable files, structured for a cold reader. ## When to Use This Skill - The user says they're about to compact, or you notice the context getting heavy mid-project - A session is ending with the project unfinished (i.e., almost every session of a real project) - Work is being handed to another agent, a fresh session, or a parallel worker - A phased plan is mid-flight — some tasks done, some in progress, some queued - You were just asked "where were we?" — the skill fired one session too late **Don't use when:** the task is single-session and will finish here; a checkpoint of a finished task is just a repor