Finding 1: IOBackend=io_uring was accepted and logged as resolved but
had no runtime effect. Now rejected by Validate() until actually wired,
preventing user confusion.
Finding 2: wal_admit_wait_seconds_total was exported as GaugeFunc but
is monotonically increasing. Changed to CounterFunc to match _total
naming convention.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>