fix· Linear
Stop in Linear stops the turn, not the whole task
Linear's Stop control used to cancel the entire workstream. It now interrupts the current turn and leaves the task in place.
Stop was wired to the same terminal signal as cancelling a task, so it took the whole workstream down and archived the sandbox, queued follow-ups included. The running turn is now interrupted within a few seconds and no pull request is opened for it.
Anything the agent had already pushed stays on the branch. Anything it had only committed inside the sandbox goes with the sandbox.
#1028