New SessionEnd plugin hook runs `claude-mailbox session-end`, which derives the session's auto-name from stdin and asks the daemon to delete the mailbox if it has no pending messages either direction. Renamed mailboxes are preserved (the auto-name no longer exists, so DELETE is a no-op). The daemon-side `SKIP_UPSERT_PATHS` prevents the request from auto-recreating the mailbox. Sweeper remains the safety net for sessions that exit ungracefully.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>