Spec Kitty

Mission Run: Concurrent writers to a Mission's files never lose or steal a write

Two agents writing the same Mission at once never silently lose, steal or corrupt each other's status, WP, tracer or claim writes.

Parallel agents on one Mission routinely overlap: implement claims, move-task, add-history, tracer-append. Today several of these writers read-modify-write or roll back without the Mission's lock, so a command that exited 0 can have its committed write erased, or two claims can both pass a single-writer check. This Mission routes every Mission-file mutation through one locked primitive and keeps ad-hoc unlocked writes out with an architectural gate.