The constructor of the Maple token calculates the chainid it should assign during its execution and permanently stores it in an immutable variable. Should Ethereum fork in the feature, the chainid will change however the one used by the permits will not enabling a user to use any new permits on both chains thus breaking the token on the forked chain permanently. (Please consult EIP1344 for more details.)
The calculation of the chainid dynamically on each permit invocation. As a gas optimization, the deployment pre-calculated hash for the permits can be stored to an immutable variable and a validation can occur on the permit function that ensure the current chainid is equal to the one of the cached hash and if not, to re-calculate it on the spot.
lucas-manuel (Maple) acknowledged:
