Provider Health

Report every configured provider's reachability, with a last-checked time.

Reuses the per-provider model-discovery test path, so a provider is healthy when its credentials can list models. Results are served from the discovery cache (cheap enough to poll), so checked_at reflects when each provider was actually dialed. Pass refresh=true to force a live re-dial of every provider. Master-key gated because it describes the gateway's own providers.

A provider whose backend serves no model-listing endpoint cannot be verified this way, but it is not unreachable either: it is reported with discovery_unsupported and counted under degraded rather than as a reachability failure.