generation-aware playback statuses

internal/playback/status_store.go

@@ -3,8 +3,9 @@ package playback
 import "sync"
 
 type StatusStore struct {
-	mu       sync.RWMutex
-	statuses map[Unit]Status
+	mu         sync.RWMutex
+	generation uint64
+	statuses   map[Unit]Status
 }
 
 func NewStatusStore() *StatusStore {
@@ -15,8 +16,15 @@ func NewStatusStore() *StatusStore {
 
 func (s *StatusStore) Observe(status Status) {
 	s.mu.Lock()
+	defer s.mu.Unlock()
+	if status.Generation < s.generation {
+		return
+	}
+	if status.Generation > s.generation {
+		clear(s.statuses)
+		s.generation = status.Generation
+	}
 	s.statuses[status.Unit] = status
-	s.mu.Unlock()
 }
 
 func (s *StatusStore) Snapshot(unit Unit) (Status, bool) {