Validate published output declarations

docs/internal/artifacts.md

@@ -184,6 +184,11 @@ For a new-protocol current state, the pointer-selected immutable commit is the
 complete restore authority. Callers receive its declared object identities and
 must not supplement them by listing mutable session prefixes.
 
+A `published_output` declaration must use a canonical publish-compatible source
+ID and an exact `runs/{run_id}/published/{destination}` key in the same session.
+Only this declaration type may refer to an earlier run; other declared objects
+remain confined to the selected commit's run.
+
 The reader opens each small control object directly and enforces owner-specific
 limits before decoding: 64 KiB for the mutable commit pointer, 4 MiB for the
 immutable commit manifest, and 8 MiB for the selected session manifest. These