rfc-conformity for cache validation

[grindhold]

Summary

redid #2891 with less code, based on the current main and with an additional test that triggers the edgecase described in #3052

Checklist

• I understand that this PR may be closed in case there was no previous discussion. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've not updated the documentation because i don't think there's anything to update