The history is process-wide, and tests cleared it only after running, and
not all of them. Records from earlier tests or an earlier -count repetition
reached later assertions: TestRecordUpstreamOperations left a record for
TestRecentFailuresNewestFirst, and the server tests never cleared it.
- Export ResetRecentFailures so tests outside the metrics package can use it
- Clear the history before and after every test that records or reads
failures directly, in metrics, server and handler
- Assert exactly one failure in the handler tests instead of looking only
at the newest
- Failure recorders take a FailureDetail: PURL, filename, URL, storage path, error
- Keep the last 20 failures per counter series in memory, reset on restart
- Strip userinfo, query and fragment from URLs, including those inside error text
- Pass the detail from upstream, storage, integrity, health probe and scan call sites
- Package names and URLs stay out of Prometheus labels
