Adding to that, about the "stealth merge", couldn't it be just the rollback? Don't change what works, as the saying goes.
And expanding on the meeting or post mortem idea, take this time not to fix the code, but to make an essay showing what broke, how it broke, and how it could be avoided in the future. Also preferably not letting your tone getting acid or those hearing from the company could instinctively refuse to listen to you even if your points are solid.