Switching a remote's backend (base_url) left the previously-cached mutable
metadata (repodata / Release / APKINDEX) served until TTL expiry, pointing
at the old upstream. cache.FlushRemote existed but was wired to nothing.
- Inject a MetadataFlusher (satisfied by *cache.Redis) into RemotesHandler.
- On update, read the existing remote first, then after a successful DB
update flush the remote's cached metadata when base_url changed so the
next request re-fetches fresh from the new upstream.
- A flush failure is logged as a warning and does not fail the request; the
DB update already landed.
- Add tests: base_url change flushes exactly once, an unchanged base_url
does not flush, and a flush error still returns 200.
unkin-agent