xsnap currently presents a JavaScript API for interacting with a single version of the xnsap-worker binary. Due to limitations in upgrading some Agoric vats (virtual workers), many will need to maintain snapshot-and-resume as their only method for restarting. Down this “legacy” track, we can only move to newer versions of xsnap-worker that are snapshot compatible, so we foresee only back-porting security fixes on this train.

Whereas, we need a new “latest” variant of xsnap that is not obliged to maintain snapshot-and-resume, for use only on vats that can restart or upgrade from a durable store and be compelled to restart whenever there’s a chain software update that might add features to “latest” xsnap that might cause a contract to behave differently or produce an incompatible snapshot.

This feature would take the form of a new variant option that is "legacy" by default and "latest" electively. The feature must preserve the current constraint that packages are built from C on the installation target machine.