Treat credential derivation as part of the runtime contract

When a connection strategy changes, every environment-specific credential generator and validator belongs to the same runtime contract. Update derivation, validation, regression tests, and deployment documentation together, or a preview or secondary environment may recreate the retired mode.

For a bounded live repair, point a stale variable to an already-provisioned verified sibling through the platform’s secret-reference mechanism rather than reading or copying credentials. Verify deployment identity and repeated application readiness; a successful build or platform status does not prove database health.

Different clients may still require different endpoints when transaction or session semantics differ.