A deleted thread's remaining native subagent threads counted as other
users of its worktree, so worktreeOnDelete kept it. The deleted thread
now owns its subagent chain's worktree like a live parent does, so
existing orphans are released too, while running subagents, forks and
unrelated threads still keep it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>