fix: harden single-machine load handling

server/store/group_message_runtime_test.go

@@ -3,6 +3,7 @@ package store
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"strconv"
 	"strings"
 	"testing"
@@ -443,6 +444,34 @@ func TestInvalidateGroupSettingsUsesTopicCacheKey(t *testing.T) {
 	}
 }
 
+func TestGetGroupMuteUsesPositiveAndNegativeCache(t *testing.T) {
+	oldRuntime := groupMsgRuntime
+	runtime := newTestGroupMessageRuntime()
+	groupMsgRuntime = runtime
+	t.Cleanup(func() { groupMsgRuntime = oldRuntime })
+
+	tenantID := types.TenantID(7)
+	topic := "grpAlpha"
+	uid := types.Uid(42)
+	cacheID := groupMemberCacheID(topic, uid)
+	expires := time.Now().UTC().Add(time.Minute)
+	want := &types.GroupMute{TenantID: tenantID, Topic: topic, UserID: uid, Status: types.GroupMuteStatusActive, ExpiresAt: &expires}
+	if err := CacheObject(tenantID, cacheNamespaceGroupMute, cacheID, groupMuteCacheValue{Found: true, Mute: want}); err != nil {
+		t.Fatalf("cache positive mute: %v", err)
+	}
+	got, err := (groupBusinessMapper{}).GetMute(tenantID, topic, uid)
+	if err != nil || got == nil || got.UserID != uid || got.Status != types.GroupMuteStatusActive {
+		t.Fatalf("positive cache result: mute=%#v err=%v", got, err)
+	}
+
+	if err = CacheObject(tenantID, cacheNamespaceGroupMute, cacheID, groupMuteCacheValue{}); err != nil {
+		t.Fatalf("cache negative mute: %v", err)
+	}
+	if got, err = (groupBusinessMapper{}).GetMute(tenantID, topic, uid); !errors.Is(err, types.ErrNotFound) || got != nil {
+		t.Fatalf("negative cache result: mute=%#v err=%v", got, err)
+	}
+}
+
 func TestTopicAndSubscriptionCacheTTLIsShort(t *testing.T) {
 	runtime := &redisGroupMessageRuntime{cfg: redisConfig{CacheTTL: 300, ShortTTL: 600}}
 	for _, namespace := range []string{cacheNamespaceTopic, cacheNamespaceSub} {