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")

server/store/candidates_test.go

@@ -37,3 +37,30 @@ func TestCandidateCacheRejectsInvalidOrDuplicateDurableProjection(t *testing.T)
 		t.Fatal("duplicate candidate accepted")
 	}
 }
+
+func TestRebuildFromQueueUsesAuthoritativeExpiryAndState(t *testing.T) {
+	now := time.Unix(1000, 0)
+	queue := domain.NewQueue()
+	active := domain.Candidate{TicketID: "ticket-active", PlayerID: "player-active", EnqueuedAt: now}
+	stale := domain.Candidate{TicketID: "ticket-stale", PlayerID: "player-stale", EnqueuedAt: now}
+	if _, err := queue.Create(active.PlayerID, active.TicketID, "create-active-123456", active, now); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := queue.Create(stale.PlayerID, stale.TicketID, "create-stale-123456", stale, now); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := queue.Cancel(stale.PlayerID, stale.TicketID, "cancel-stale-123456", 0, now); err != nil {
+		t.Fatal(err)
+	}
+	cache := NewCandidateCache()
+	if err := cache.Upsert(domain.Candidate{TicketID: "obsolete", PlayerID: "obsolete", EnqueuedAt: now}); err != nil {
+		t.Fatal(err)
+	}
+	if err := RebuildFromQueue(cache, queue, now); err != nil {
+		t.Fatal(err)
+	}
+	got := cache.Snapshot(now)
+	if len(got) != 1 || got[0].TicketID != active.TicketID {
+		t.Fatalf("authoritative rebuild = %+v", got)
+	}
+}