Unify layered provenance history

records.go

@@ -150,7 +150,8 @@ type Diagnostic struct {
 }
 
 // Origin describes where an effective definition came from. Multiple locations
-// represent a composite origin.
+// represent a composite origin; resolution origins are synthetic and identify their
+// operation instead of a file location.
 type Origin struct {
 	Layer     Layer
 	Locations []Location
@@ -164,8 +165,9 @@ type FieldInfo struct {
 	Origin   Origin
 }
 
-// Change describes a definition or application-resolution operation. Historical
-// values are intentionally not exposed by this record.
+// Change describes a definition or application-resolution operation. Path can name
+// an ancestor operation affecting the queried descendant. Historical values are
+// intentionally not exposed by this record.
 type Change struct {
 	Path         Path
 	Origin       Origin