DNS names are case-insensitive, so a backend named back in a different
case escaped redaction and reached the client.
- Fold ASCII case when replacing a backend's URL, host and hostname
- Pin the redaction vectors, the same-status rule and the bare-GET
premise behind treating 406 and 415 as replayable
Every backend gets the same query, so one they all refuse is the client's
mistake; flattening it into "all backends failed" threw openvoxdb's own
explanation away and logged a typo as an outage.
- Carry status, content type and body on a typed upstreamError
- Replay the status and explanation when every backend refuses alike
- Redact backend addresses from replayed bodies
- Keep a refused query out of the partial counters and the cache
unkin-agent