Technically FLP impossibility only applies to deterministic algorithms, not randomized ones, otherwise no consensus protocol would work. So you could imagine a

Technically FLP impossibility only applies to deterministic algorithms, not randomized ones, otherwise no consensus protocol would work. So you could imagine a complicated technical solution that could work (eg. treating everything as a big Raft cluster and using Raft's membership changes every time a device is connected / disconnected). In practice the solution is to realize that failures are rare (especially compared to events like the soldier simply misplacing the card), and to have a trusted human available to resolve any issues that do occur.