SitePskProvider cached each site's gRPC preshared key forever; only site removal
invalidated it, so rotating SB-GRPC-PSK-{site} broke the central<->site link on
both central nodes until they restarted. The cached key is now dropped when:
- the secret is written through /admin/secrets: central replaces the secrets
library's ISecretCacheInvalidator with SitePskRotationInvalidator, which also
publishes SitePskInvalidated on a new DistributedPubSub topic
(site-psk-invalidation) so the peer central node drops its copy and its
resolver cache entry too (SitePskInvalidationSubscriber);
- a site rejects a central->site call with PermissionDenied/Unauthenticated:
WithSiteCredentials wraps every per-site channel's handler in
PskRejectionRefreshHandler, so the next call re-reads the key (covers
out-of-process writes such as the secret CLI);
- a site->central call presents a token that does not match the cached key:
CentralControlAuthInterceptor invalidates and re-reads once before refusing;
- ScadaBridge:Communication:SitePsks reloads.
Invalidation is case-insensitive because SecretName lowercases names. Rotation
runbook (topology-guide), Component-Communication/Host and the #85 cache audit
(D2) updated.
Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV
Joseph Doherty