A persisted placeholder is useless if shutdown deletes the ref it tracks.
Leave pending refs and their objects on disk alongside the final purgatory
checkpoint; expiry remains responsible for removing abandoned uploads.
Update the runtime description and add a SIGTERM regression test.
Assume normal Git persistence and the existing checkpoint lifecycle.
Crash recovery and object compaction remain separate changes.
Validation: nix develop -c cargo test --test purgatory
graceful_shutdown_keeps_pending_pr_refs passed, observing process exit and
the surviving ref and commit without fixed sleeps.
Assisted-by: GPT-6