Strengthen validation retries and checkpoint safety

docs/internal/modules.md

@@ -45,6 +45,15 @@ they need, register each leaf implementation, and add any family-owned assets
 or default validator chains. They return contextual errors so production
 composition fails at startup rather than at the first run.
 
+A validator that returns a completed rejection must supply two separate
+bounded values: a stable `ReasonCode` for provenance and actionable
+`CorrectionGuidance` for the producer. Guidance identifies the semantic defect
+and the constraints on one complete corrected replacement. It must not contain
+validator keys, diagnostic paths, opaque application IDs, or other internal
+identifiers. An operator-facing `Message` may explain the same event, but the
+framework never copies it into a model request. Missing or invalid guidance is
+a validator contract failure.
+
 An artifact family can register an optional typed evidence projector alongside
 its codec. The projector returns defensive copies of the artifact's direct
 generic source references and must use the codec's exact Go type. It does not
@@ -131,6 +140,8 @@ its domain prompt.
 4. Register the module through its typed registry helper and add it to the
    owning family registrar. Add a default validator chain only when that
    family owns the behavior; otherwise require an explicit compatible chain.
+   Every rejection path in a validator must provide actionable correction
+   guidance while retaining its stable internal reason code.
 5. Update the selectable-key and chain reference in
    [Configuration](../config.md#production-module-keys), the applicable
    integration contract, and focused tests. Keep the configuration document