Module undo 

Undo system for queue mutations.

Responsibilities:

• Create snapshots before queue-modifying operations.
• List available snapshots for undo.
• Restore queue state from snapshots.
• Prune old snapshots to enforce retention limits.

Not handled here:

• CLI argument parsing (see cli::undo).
• Queue lock acquisition (callers must hold lock).

Invariants/assumptions:

• Snapshots capture BOTH queue.json and done.json atomically.
• Snapshots are written atomically via fsutil::write_atomic.
• Callers hold queue locks during snapshot creation and restore.

Structs

RestoreResult

Result of a restore operation.

SnapshotList

Result of listing snapshots.

UndoSnapshot

Full snapshot content (stored in JSON file).

UndoSnapshotMeta

Metadata about a single undo snapshot.

Functions

create_undo_snapshot

Create a snapshot before a mutation operation.

list_undo_snapshots

List available undo snapshots, newest first.

load_undo_snapshot

Load a full snapshot by ID.

prune_old_undo_snapshots

Prune old snapshots to enforce retention limit.

restore_from_snapshot

Restore queue state from a snapshot.

undo_cache_dir

Get the undo cache directory path.