fix: rebuild candidate cache from queue authority

server/store/candidates.go

@@ -20,6 +20,17 @@ func NewCandidateCache() *CandidateCache {
 	return &CandidateCache{candidates: make(map[string]domain.Candidate)}
 }
 
+// RebuildFromQueue is the safe restart/failover path for the cache. Queue
+// expiry and state filtering happen at the authoritative source before the
+// cache is atomically replaced; callers never have to reconstruct those
+// rules from a stale Redis index.
+func RebuildFromQueue(cache *CandidateCache, queue *domain.Queue, now time.Time) error {
+	if cache == nil || queue == nil || now.IsZero() {
+		return fmt.Errorf("invalid candidate rebuild arguments")
+	}
+	return cache.Rebuild(queue.Candidates(now))
+}
+
 func (c *CandidateCache) Upsert(candidate domain.Candidate) error {
 	if candidate.TicketID == "" || candidate.PlayerID == "" || candidate.EnqueuedAt.IsZero() {
 		return fmt.Errorf("invalid candidate")