See the first diff in the stack. We're no longer expecting to see such an old codeVersion, so I'm going to delete this code.
This is admittedly slightly more risky than some of the other diffs in the stack, because this doesn't just break the USE of such an old codeVersion, but rather breaks the upgrade FROM such an old codeVersion.
However, I think it's safe because we don't currently have any logged-in sessions with such an old codeVersion, and we prevent log in / registration with such an old codeVersion in the parent diff. So we don't expect such an upgrade to occur.
Depends on D8503
I thought putting an invariant here was a reasonable trade-off vs. refactoring the types in the fullStateSyncActionType payload (specifically StateSyncFullActionPayload which is derived from ClientFullStateSync which is derived from BaseFullStateSync) which are used across clients and keyserver.
Open to re-exploring if that would be preferred.