Just a guess, but the attack is probably something like the coordinator doing lots of useless rounds to slowly drain user funds to coordinator fees.

A good defense for this type of problem in general would be to set a limit on how much Wasabi is willing to spend in fees for coinjoins over a given time period. Eg no more than 0.5% of your wallet value per day.

It would also be useful to be able to tell Wasabi to do no more than N coinjoins in this session, and then stop so the user can look at what is happening.