Add receive support for pin/unpin message

ts/messageModifiers/helpers/isValidSenderAciForConversation.preload.ts

@@ -0,0 +1,19 @@
+// Copyright 2025 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import type { AciString } from '@signalapp/mock-server/src/types';
+import type { ConversationModel } from '../../models/conversations.preload.js';
+import { itemStorage } from '../../textsecure/Storage.preload.js';
+
+export function isValidSenderAciForConversation(
+  conversation: ConversationModel,
+  senderAci: AciString
+): boolean {
+  const ourAci = itemStorage.user.getCheckedAci();
+
+  if (senderAci === ourAci) {
+    return true;
+  }
+
+  return conversation.hasMember(senderAci);
+}