29049c4ef6
Secret-store outage (final review M5): SiteSecretsCollector returns a store read failure as SiteSecretsCollection.StoreError instead of throwing. A deploy now fails only the sites that reference a secret (nothing sent, not stamped, DeploySiteSecrets row with the error), and ComputeCurrentArtifactHashesAsync omits only those sites (they read Out of date) instead of the exception aborting the whole sweep and the fleet-wide pending-updates check. Removal-only deploys: the site reply gains SecretsRemoved (proto field 7, names only) - the deployed_secrets rows the deploy soft-removed. Central carries it on SiteArtifactResult and writes the DeploySiteSecrets row with a removed list whenever it is non-empty, so dropping a site's last secret: reference is audited centrally rather than only in site logs.