shared-service-reuselisted

# Shared services: one codebase, N independent instances **Read [`references/SHARED-SERVICE-REUSE.md`](references/SHARED-SERVICE-REUSE.md) before applying any of this.** That file is the standard; everything below it is a summary to help you decide whether this skill applies and to check your work afterwards. Reference-architecture principles: P2, P3, P7. ## What this standard covers - One codebase, N independent instances - An artifact dependency, never a source dependency - Publishing must not depend on deploying - Each consumer names its own instance - Database per instance, reconciled with P3 - What this does not excuse ## Failure modes | Symptom | Cause | |---|---| | Two consumers' users can authenticate against each other's system | A shared trust root: the same signing key was reused across instances, so the tokens are mutually valid. Independent instances means independent key material (§1) | | A consumer is running software nobody can identify | The image reference is `:latest`. Two consumers that deployed a week apart are on different builds while their config claims otherwise (§2) | | The shared service cannot ship a release | The publish job was gated on the service's own deployment secrets, so a maintainer without a hosted instance cannot publish for consumers who need one (§3) | | An upgrade to one consumer takes another consumer down | The two are not independent instances at all — somewhere a runtime edge was introduced, usually a "temporary" pointer at