# Letterpress usage rules

## Compile before publication

Call `Letterpress.compile/4` when validating preview or publication. Persist the
complete returned artifact for every deliverable locale. A compiler error is an
authoring/publication failure, not a reason to fall back to another renderer.

## Render stored artifacts

Call `Letterpress.render/3` at delivery with resolved values. Delivery nodes may
omit `Letterpress.Compiler.Supervisor`; valid stored artifacts still render
without Node.

## Keep application policy in the host

The host owns authorization, tenancy, locales, publication state, retries,
providers, and migrations. Convert legacy formats into a Letterpress profile
before calling the normal compiler. Do not add a permissive migration mode.

## Treat diagnostics as untrusted structured data

Match on diagnostic codes and ranges, not English prose. Escape messages in
the UI. Correlate asynchronous responses with `source_hash` and
`document_version` before displaying them.

## Do not persist resolved values

Artifacts contain expressions and compiler provenance, not recipient data or
secrets. Never place source, rendered output, or variable values in telemetry.