Document and benchmark sibling inheritance

records.go

@@ -205,8 +205,9 @@ type Diagnostic struct {
 	Related  []Location
 }
 
-// InheritanceStep identifies a concrete payload transfer controlled by a
-// relationship directive. Locations belong to that directive, not its value.
+// InheritanceStep identifies a concrete payload transfer. From and To name
+// semantic value paths; Reference names the controlling destination `extends`
+// path. Locations belong to that directive, not the transferred value.
 type InheritanceStep struct {
 	From      Path
 	To        Path
@@ -216,7 +217,8 @@ type InheritanceStep struct {
 
 // Origin describes where an effective definition came from. Multiple locations
 // represent a composite origin; resolution origins are synthetic and identify their
-// operation instead of a file location.
+// operation instead of a file location. Inheritance records the concrete
+// derivation path while Layer and Locations continue to identify value sources.
 type Origin struct {
 	Layer       Layer
 	Locations   []Location