Agent worktrees with isolation:worktree not cleaned up when calling session ends

Summary

When the Agent tool is used with isolation: "worktree", Claude Code creates a git worktree and locks it with the calling process's PID. If the calling session ends before the agent completes (or before cleanup runs), the worktree is stranded — locked, never pruned, and orphaned forever.

Reproduction

1. Launch an Agent with isolation: "worktree" from a Claude Code session
2. End the session (context limit, crash, or manual exit) before the agent returns
3. Start a new session in the same repo
4. Run git worktree list — orphaned locked worktrees appear

Observed state

Found 6 locked worktrees in .claude/worktrees/, all pointing to the same old commit, all locked with PID 197259 (long dead):

~/code/personal/boxy-green-thing/.claude/worktrees/agent-a1761c25a0d171d29  [locked]
~/code/personal/boxy-green-thing/.claude/worktrees/agent-a27eed21738882d75  [locked]
...

Lock reason string: claude agent agent-<id> (pid 197259) — the PID no longer exists.

Expected behavior

Claude Code should clean up orphaned agent worktrees on session start (or offer to). At minimum, a git worktree prune equivalent that checks whether the locking PID is still alive would clear stale locks automatically.

Workaround

git worktree remove -f -f .claude/worktrees/<name>
git worktree prune
git branch | grep worktree-agent | xargs git branch -D

Requires double --force because the lock explicitly blocks single --force removal.

Environment

• Platform: Linux (WSL2)
• Shell: zsh