<!-- swain-model-hint: sonnet, effort: medium -- Session Teardown Single entry point for ending a session. Runs the full shutdown sequence: digest, retro, merge, cleanup, close, commit. Replaces the former swain-session close handler (ADR-023). If is NOT passed and the JSON output has other than , inform the operator: "No active session to tear down." Exit cleanly with code 0. --- What this skill does Session teardown runs a sequence of hygiene checks before a session closes: 1. Orphan worktree detection — finds worktrees with no corresponding session bookmark (SPEC-233: actionable with safet…