Inbox `cancel` Test Plan Index

Case Files

Case Slug	File	Coverage Note
`cancel-marks-thread-cancelled`	cancel-marks-thread-cancelled.md	moves a non-terminal thread into `cancelled` and emits a control message
`cancel-persists-reason-and-artifact`	cancel-persists-reason-and-artifact.md	persists cancel reason text and attached artifacts
`cancel-rejects-when-thread-missing`	cancel-rejects-when-thread-missing.md	returns stable not-found contract when thread does not exist