merged with fixes

internal/rpc/presence_work.go

@@ -0,0 +1,41 @@
+package rpc
+
+// PresenceWorkSnapshot measures pending grace callbacks and their last-seen
+// writers, including online last-seen work in the shared batch. It is not a
+// durability receipt or an inventory of all router background work.
+type PresenceWorkSnapshot struct {
+	WaitingTimers    int64
+	RunningCallbacks int64
+	DirectWrites     int64
+	PendingLastSeen  int64
+}
+
+// PresenceWorkSnapshot is bounded and identity-free. Holding the tracker lock
+// across the batch read prevents a false zero at callback -> batch handoff:
+// submission precedes the callback's locked running-count decrement.
+func (r *Router) PresenceWorkSnapshot() PresenceWorkSnapshot {
+	if r == nil || r.presence == nil {
+		return PresenceWorkSnapshot{}
+	}
+	p := r.presence
+	p.mu.RLock()
+	defer p.mu.RUnlock()
+	s := PresenceWorkSnapshot{
+		WaitingTimers:    int64(len(p.offlineTimers)),
+		RunningCallbacks: p.offlineRunning,
+		DirectWrites:     p.lastSeenDirectRunning,
+	}
+	if r.lastSeenBatch != nil {
+		s.PendingLastSeen = r.lastSeenBatch.pending.Load()
+	}
+	return s
+}
+
+func (p *presenceTracker) changeDirectLastSeenRunning(delta int64) {
+	if p == nil {
+		return
+	}
+	p.mu.Lock()
+	p.lastSeenDirectRunning += delta
+	p.mu.Unlock()
+}