Edge key-value store

Design an edge key-value store (like a global config/feature-flag store) that serves reads from 200 POPs with single-digit-ms latency worldwide, while writes from a central control plane must converge everywhere within a bounded time. Reads vastly outnumber writes, occasional read staleness is acceptable, but a flag flip must be globally visible within ~5s and must never 'flap' back to the old value. Design replication, the read/write paths, and the consistency model.