fix(lock): renew distributed locks via heartbeat; wire server refresh (backlog#899)
A held distributed write lock had a fixed 30s TTL and was never renewed, so
any operation exceeding it got its per-node lease reclaimed and stolen by a
contender, causing split-brain writes. This implements Phase 0 + Phase 1 of the
#899 design (Phase 2 abort-on-loss is deferred and tracked in code comments).
Phase 0 (server refresh wiring, P0):
- node_service handle_refresh was a no-op stub that parsed args then always
returned success=true. Extract a testable `refresh_lock` free function that
actually delegates to the node's lock backend. Not-found maps to
success=false with no error_info, so RemoteClient::refresh keeps its
Ok(resp.success) semantics and yields a real not_found signal to the
coordinator heartbeat. Without this, client heartbeats were silently no-ops.
Phase 1 (client heartbeat + safe interval + observability):
- DistributedLockGuard spawns a heartbeat that refreshes every per-client lease
on a derived interval; interval is derived without Duration::clamp
(entries<=1 or interval>=ttl => no spawn), fixing the sub-second-ttl panic.
- Add LockLostSignal: declare the lock lost when not_found exceeds
entries.len() - refresh_quorum; RPC errors are not counted (absorbed by the
ttl > interval margin). Expose is_lock_lost()/lock_lost() for observers.
- disarm(), release(), and Drop now abort the heartbeat before releasing so no
refresh races the unlock (refresh only extends, never creates, a lease).
- Reclaim path stays behaviorally unchanged but now warns with owner/resource/
lease age and records a metric (#698 scavenger preserved).
- Add DEFAULT_LOCK_REFRESH_INTERVAL, LockRequest.refresh_interval (serde default
for RPC back-compat) + builder, and lock lifecycle metrics.
Open questions adopt the design's documented defaults (marked TODO in code):
refresh not-found -> Ok(false)/error_info=None; lost-quorum base entries.len();
DEFAULT_LOCK_REFRESH_INTERVAL=10s.
Tests: heartbeat keepalive/quorum-loss/jitter/boundary/disarm (lock crate),
server refresh delegation (rustfs), and end-to-end survives-past-ttl plus
crashed-owner-reclaim regressions (namespace).
Zhengchao An