Validate portable workspace identifiers

docs/internal/artifacts.md

@@ -30,9 +30,11 @@ and content validator. The focused stage documents own their input/output flow;
 - extraction source ID format: `narratio.extraction.<output_key>`
 - previous-session source ID format: `narratio.previous_session.artifact.<artifact_key>`
 
-All formats are validated by strict source-policy rules. Extraction sources are
-registered only from `pipeline.notarius.outputs`; the Notarius index has no
-selectable source ID.
+All formats are validated by strict source-policy rules. Configured artifact and
+extraction keys use `^[a-z][a-z0-9_]*$`; source parsers never normalize an
+unrecognized token into a valid source. Extraction sources are registered only
+from `pipeline.notarius.outputs`; the Notarius index has no selectable source
+ID.
 
 ## Runtime Catalog
 
@@ -131,6 +133,12 @@ Caller policy is intentionally outside artifacts helpers:
 - spool/cache paths;
 - S3 session/run/current-state key layout.
 
+Campaign, session, and Narratio run IDs are validated as portable opaque
+segments at configuration and artifact boundaries before they can be used in a
+workspace or S3 namespace. Previous-artifact destinations remain typed,
+multi-segment relative paths and are confined beneath `previous/artifacts`; they
+are not treated as opaque identifiers.
+
 See [Workspace Internals](workspace.md) for how callers consume local helpers
 and [Operations](../operations.md#local-state-layout) for the authoritative
 physical layout.