Check native overlay link targets

docs/config.md

@@ -1529,6 +1529,10 @@ base import graph is composed and its schema version is checked, but before defa
 and typed decoding. Overlay bytes, nodes, and source records count toward the same
 aggregate limits as base inputs. Its canonical path must remain within the configured
 root and must not duplicate a file already present in the base graph.
+For native filesystems that implement `fs.ReadLinkFS`, these checks resolve
+link targets in the selected namespace. For other native filesystems, the
+checks use namespace-relative paths and reads follow that filesystem's
+ordinary behavior.
 
 Collection destinations follow the
 [collection operation and presence rules](#strict-document-composition) above.