mCallbacks 保存在 client 进程，在 TransactionCompletedListener::onTransactionCompleted() 中根据 CallbackId 查找 callbackFunction。

std::unordered_map<CallbackId, CallbackTranslation, CallbackIdHash> mCallbacks
        GUARDED_BY(mMutex);

• Key 是 CallbackId。
• Value 是 TransactionCompletedListener::CallbackTranslation。

graph TD
  mCallbacks --> map[CallbackId -> CallbackTranslation]
  map -.- CallbackId
  CallbackId --> id
  CallbackId --> type
  map -.- CallbackTranslation
  CallbackTranslation --> callbackFunction:TransactionCompletedCallback
  CallbackTranslation --> map2[IBinder -> SurfaceControl]