If the upstream responds with broken states, Relay attempts to reuse old caches as long as possible. However, if there is no cache, Relay immediately drops envelopes. Our stability SLO suggests that we should buffer envelopes instead until they timeout.

To achieve this behavior, we will have to:

• Leave envelopes in the queue when states are invalid
• Expire queued envelopes when a timeout has been reached
• Check whether there should be a timeout on the envelopes or rather on the project state

Created from #1767 (comment)