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A Designer could point a Galaxy / OpcUaClient endpoint at a host they control, set a credential field to any reference the node can resolve (env:ConnectionStrings__ConfigDb, env:ServerHistorian__ApiKey, secret:<any>, Galaxy file:<any path>) and click Test Connect / live browse; the node resolved the value and sent it to that host. One shared rule in Core.Abstractions (CredentialReferences + DriverCredentialPolicy) generalises the #803 Heidenhain namespace: - Galaxy: secret:galaxy/... | secret:otopcua/galaxy/... | env:OTOPCUA_GALAXY_... | legacy env:GALAXY_MXGW_...; file: refused; dev:/literal API key unchanged. - OpcUaClient: secret:opcuaclient/... | env:OTOPCUA_OPCUACLIENT_...; literals unchanged. - Heidenhain adopts the shared parser/resolver (namespace unchanged). Enforced at the AdminUI save path (DriverConfigSaveGate), the deploy gate (CredentialReferenceDeployChecks, code CredentialReferenceOutOfScope), Test Connect (AdminOperationsActor, before any probe), live browse (BrowserSessionService, before any browser) and again at resolve time in every driver/browser (fail closed, before any store/env read). Co-Authored-By: Claude <noreply@anthropic.com>