It looks to me like at the original fork point, Bitcoin-ABC added an extra value
SIGHASH_FORKID that is xor'ed with the standard SIGHASH flags to produce a SIGHASH byte that is incompatible with Bitcoin Core. This provides replay protection for all transactions that are signed with ECDSA pubkeys.
FORKID updated with each "protocol upgrade" for example the recent "Magnetic Anomaly" upgrade? If not, why not?
It looks like the May 2019 upgrade will change the
0xFF0001 but the spec mentions "Wallets that follow the upgrade should not have to change anything." -- how is that possible?
Did Bitcoin-SV change its
FORKID for its recent hard fork away from Bitcoin-ABC? Is there any replay protection at all between those two chains?