We should probably assert in the order validator (which is used in roachtests, changefeed nemeses etc) that resolved messages are monotonic. You should never see a regression in the resolved messages.

I started a draft PR #108861. C2C streaming tests fail because you see resolved messages that go back in time. I don't know if this is expected for streaming. Nevertheless, the PR needs a bit more work.

Jira issue: CRDB-30676