feat: use message LCP cache affinity keys

apps/api/internal/store/cache_affinity.go

@@ -7,6 +7,7 @@ import (
 
 type CacheAffinityObservationInput struct {
 	CacheAffinityKey       string
+	CacheAffinityKeys      []string
 	CacheAffinityPolicy    map[string]any
 	PlatformID             string
 	PlatformModelID        string
@@ -19,9 +20,10 @@ type CacheAffinityObservationInput struct {
 
 func (s *Store) RecordCacheAffinityObservation(ctx context.Context, input CacheAffinityObservationInput) error {
 	input.CacheAffinityKey = strings.TrimSpace(input.CacheAffinityKey)
+	input.CacheAffinityKeys = normalizedCacheAffinityKeys(input.CacheAffinityKey, input.CacheAffinityKeys)
 	input.ClientID = strings.TrimSpace(input.ClientID)
 	input.ModelType = strings.TrimSpace(input.ModelType)
-	if input.CacheAffinityKey == "" || input.ClientID == "" || input.ModelType == "" {
+	if len(input.CacheAffinityKeys) == 0 || input.ClientID == "" || input.ModelType == "" {
 		return nil
 	}
 	if !input.CachedInputTokensKnown || !cacheAffinityPolicyEnabled(input.CacheAffinityPolicy, input.ModelType) {
@@ -39,6 +41,15 @@ func (s *Store) RecordCacheAffinityObservation(ctx context.Context, input CacheA
 	}
 	alpha := cacheAffinityEMAAlpha(input.CacheAffinityPolicy)
 	hitRatio := float64(input.CachedInputTokens) / float64(input.InputTokens)
+	for _, key := range input.CacheAffinityKeys {
+		if err := s.recordCacheAffinityObservationKey(ctx, input, key, hitRatio, alpha); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func (s *Store) recordCacheAffinityObservationKey(ctx context.Context, input CacheAffinityObservationInput, key string, hitRatio float64, alpha float64) error {
 	_, err := s.pool.Exec(ctx, `
 	INSERT INTO gateway_cache_affinity_stats (
 	  client_id, cache_affinity_key, platform_id, platform_model_id, model_type,
@@ -60,7 +71,7 @@ func (s *Store) RecordCacheAffinityObservation(ctx context.Context, input CacheA
 	    last_observed_at = now(),
 	    updated_at = now()`,
 		input.ClientID,
-		input.CacheAffinityKey,
+		key,
 		input.PlatformID,
 		input.PlatformModelID,
 		input.ModelType,