Before deploying updated Pub/Sub subscriber code that might incorrectly acknowledge messages and you do not retain acknowledged messages, how can you recover messages if deployment causes message loss?

Creating a Pub/Sub snapshot before deployment is the most robust way to recover messages if the new subscriber code causes message loss due to incorrect acknowledgments. A snapshot retains a copy of all messages in the topic's backlog at the time of creation. If messages are lost, you can use a Seek operation on the subscription, referencing the snapshot, to re-deliver all messages that were in the topic's backlog when the snapshot was taken, including those that might have been incorrectly acknowledged. The Pub/Sub emulator is for local testing, not production recovery. Cloud Build logs timestamps but doesn't provide a mechanism to recover lost Pub/Sub messages directly. Dead-lettering captures messages that a subscriber fails to acknowledge, not messages that are incorrectly acknowledged and thus removed from the topic.