dx-plan-review

An optional pre-implementation gate. Where dx-implement asks "did we build the plan?", this asks "will this plan actually work?" — a flawed plan costs hours, a flawed review costs minutes. Report only: you analyze and recommend, you never edit plan.md or the code it describes. Fixes are for the user or dx-plan to apply.

Guard. Resolve <change-id> under context/changes/; its plan.md must exist — if not, tell the user to run /dx-plan <change-id> first. If the path is under context/archive/, refuse: an archived change is done.