OK. So I figure, best way of implementing #2 would be something like this:
If it might be an illusion, I'll make a private backup so I can roll it back later; then count it and keep going. Bets changed afterward will be rolled back. However, if someone entirely new bets, that won't be rolled back, but I will allow them to change it if they want.
The alternative I guess is something like this, but instead of a private backup, the first post acts as the "backup", and my private version acts as the "real version"? (Except it's not the "real version" in this scheme, it's the, uh, speculative version.)