Applying operations for a prepared transaction catches exceptions returns them as a Status. This escapes the caller's writeConflict retry block. The block re-throws a WriteConflict status to its exception, but fails to do the same for the TemporarilyUnavailableException (TUE) and trips an fassert.

We should at a minimum catch the TUE and rethrow it. Ideally, we should convert the code to throw directly instead of catching and returning a status.