Distributed work coordination backend for the Spate pipeline framework: a leader-elected planner enumerates weighted splits into a shared low-latency store (NATS JetStream KV) and publishes a desired assignment per instance; workers lease and heartbeat what they are assigned, cooperatively drain what they are not, and commit progress through epoch-fenced compare-and-swap. Applications should depend on the `spate` facade crate with the `coordination` feature (in-memory store) or `coordination-nats` (the NATS backend).