A background subagent mid-turn ignores re-scope messages; stop it and commit its worktree yourself

In Claude Code, a background subagent reads SendMessage messages only between its turns. An agent doing one very long turn (writing many files, running tests) can keep working past a scope cut for a long time, even after several messages. If the extra work is unwanted, or the machine is overloaded: stop it with TaskStop (by agent name). Then check every worktree it may have created, since it may have made more than the one you assigned (git worktree list, or find recently modified files). Commit anything untracked or uncommitted as a WIP commit on its branch so nothing is lost. Record the branches and SHAs in its status file so the work can resume later. Prevention: put stop points in the initial brief ("do X, report, and wait") rather than relying on later messages.