fix: resolve P1 backend consistency issues

server/store/group_message_runtime_test.go

@@ -9,8 +9,9 @@ import (
 )
 
 type testGroupMessageRuntime struct {
-	claims map[string]*groupMessageUniqueRecord
-	seqs   map[string]int64
+	claims          map[string]*groupMessageUniqueRecord
+	seqs            map[string]int64
+	deletedPrefixes []string
 }
 
 func newTestGroupMessageRuntime() *testGroupMessageRuntime {
@@ -116,6 +117,11 @@ func (r *testGroupMessageRuntime) DeleteCachedObject(types.TenantID, string, str
 	return nil
 }
 
+func (r *testGroupMessageRuntime) DeleteCachedObjectsByPrefix(_ types.TenantID, _ string, prefix string) error {
+	r.deletedPrefixes = append(r.deletedPrefixes, prefix)
+	return nil
+}
+
 func (r *testGroupMessageRuntime) AddCachedSetMember(types.TenantID, string, string, string) error {
 	return nil
 }
@@ -176,3 +182,15 @@ func TestMessageRuntimeSeqAndClientMidIdempotency(t *testing.T) {
 		t.Fatalf("unexpected second seq: seq=%d ready=%v err=%v", seq, ready, err)
 	}
 }
+
+func TestInvalidateGroupMemberPagesUsesTopicKeyPrefix(t *testing.T) {
+	oldRuntime := groupMsgRuntime
+	runtime := newTestGroupMessageRuntime()
+	groupMsgRuntime = runtime
+	t.Cleanup(func() { groupMsgRuntime = oldRuntime })
+
+	invalidateGroupMemberPages(7, "grpAlpha")
+	if len(runtime.deletedPrefixes) != 1 || runtime.deletedPrefixes[0] != "grpAlpha|" {
+		t.Fatalf("unexpected deleted prefixes: %#v", runtime.deletedPrefixes)
+	}
+}