Whether a value is a checkpoint of this screen, read synchronously from the
id it carries and nothing else. A checkpoint is an object (owner decision,
2026-10-24: never JSON text — a caller parses what its storage returns), so
text answers false. For an object type it is a type guard, so after it any
of the restores of the same screen cannot refuse with a mismatch; unknown
answers a plain boolean. A corrupt checkpoint still fails the restore with
CheckpointDecodeError.
Whether a value is a checkpoint of this screen, read synchronously from the id it carries and nothing else. A checkpoint is an object (owner decision, 2026-10-24: never JSON text — a caller parses what its storage returns), so text answers
false. For an object type it is a type guard, so after it any of the restores of the same screen cannot refuse with a mismatch;unknownanswers a plainboolean. A corrupt checkpoint still fails the restore withCheckpointDecodeError.