Module checkpoint 

Structs

CheckpointFile

CheckpointManifest

Functions

create_checkpoint

create_checkpoint_for_task

gc_old_checkpoint_dirs

Best-effort GC of on-disk checkpoint directories older than retention_days (#130): removes checkpoints/<id>/ whose mtime is past the window so the tree can’t grow without bound, while keeping recent (still-restorable) checkpoints. Returns the count removed; never fails the caller (a bad entry is skipped).

restore_checkpoint