When an isolated agent's worktree has been removed externally and the only fallback would be running in the parent session's shared checkout, the agent now refuses to run and reports the problem:
"This agent is isolated in the worktree <path>, but its working directory <cwd> no longer exists and the only recovery target is the parent session's shared checkout. Refusing to run there — the isolation worktree appears to have been removed. Report this instead of retrying."
Previously the agent might silently run commands in the parent directory.
Evidence
Isolation safety check (search for "Refusing to run there — the isolation worktree appears to have been removed")
Strings lifted out of the shipped bundle, so the claim above can be checked against them.