Bounded-staleness follower reads

A globally-replicated database (one leader per range, async followers in other regions) wants to serve reads from the local follower for latency, but stale-follower reads break two guarantees users notice: read-your-own-writes (a user updates their profile, then re-reads from a follower and sees the OLD value) and monotonic reads (a later read returns older data than an earlier one). Design the follower-read mechanism that gives bounded-staleness or consistent local reads without sending every read to the leader, and the trade-off between latency and freshness.