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Failover routes a session behind its observed version · case 05

The fastest replica returns data older than a version this session has already seen.

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Case contract

Replicas are [ID,applied version,latency]. Return [ID,version] for the minimum (latency,ID) among versions >= session floor, or None if no replica qualifies. Version order is globally comparable in this model.

Why this case matters

Models session-consistent replica routing after a client moves between read endpoints, including the distinction between a required consistency floor and unnecessarily seeking the newest state.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
stale fast replica	`["a", 14]`	`["b", 15]`	Failed

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