Dealing with a forgotten boule

[updated 2021-06-11]
What do you do when one team forgets that it has an unplayed boule?

There are a lot of boules on the ground. Your team (team A) has the point and unplayed boules. You ask the opponents (Team B) if they have any more boules to play. They look around, don’t see any, and say “No, we’re out.” So your team plays a boule. Then one of the opponents says “Ooops! I made a mistake. Bob still has one boule left!”

 
What should you do?

Team B had an unplayed boule and was given the opportunity to play next, but refused to do so. Team B therefore was at fault and may not play its forgotten boule. It makes no difference that Team B acted because of a mistake rather than a deliberate desire to cheat. Team B’s forgotten boule is dead.

Note that allowing Team B to throw its forgotten boule would allow Team B to gain an advantage from breaking the rules— it would steal the boule advantage from Team A. On the grounds that a team should never be able to gain any advantage by breaking the rules, Team B may NOT play their forgotten boule.

Note that the situation would be different if Team A had simply gone ahead, without asking Team B if they had any unplayed boules. That would be an ordinary case of a boule thrown out of turn.