Expand description
Leader-side replication server for FixedStore.
- Spawns a TCP acceptor thread.
- On the first accepted follower connection, installs SPSC producers into every shard (lazy install — Mitigation B of spec §5/§7).
- Each accepted connection spawns a per-shard serve thread that does Phase 1 (full scan catch-up, honoring FLAG_EMPTY_STATE to skip DELETED slots) then Phase 2 (SPSC streaming) if the per-shard consumer is still available.
Single-follower-streaming-per-shard constraint: the SPSC consumer for
each shard is held by at most one connection at a time. If a concurrent
follower tries to claim a consumer that is already taken the server sends
an Error frame and returns, letting the client reconnect later. When a
connection finishes (cleanly or on error), ShardConsumerGuard::drop
returns the consumer to the pending slot so the next connection can
claim it and enter Phase-2 streaming.