URL version boundary
Stable public API routes live under `/api/v1`. A caller may send `X-Lucion-API-Version: 1` to explicitly request that contract. The server includes the same header on API responses. Unsupported requested versions receive `406`.
Compatibility policy
Within a version, additive optional response fields may be introduced. Existing fields, scope requirements, validation boundaries, and status semantics should remain compatible. Breaking behavior should receive a new version boundary and a dated changelog entry.
Application release manifest
The public `/release-manifest.json` describes the deployed application release, not the API schema. Older open clients compare it with their compiled version and show the Lucion Release Update Banner when the remote version is newer. The manifest is served with `no-store` cache behavior.
Release communication
Every Helios Post update records its version, release name, date, behavior changes, migration requirements, and verification status in the changelog. Keep the supplied Lucion Release Update Banner Kit active and test the production manifest after deploy.