Activate sibling inheritance in configuration loading

records.go

@@ -32,7 +32,10 @@ type ChangeKind string
 const (
 	// ChangeDecoding records the built-in transition to canonical typed values.
 	// It is inspection metadata, not an operation accepted by Resolution.Record.
-	ChangeDecoding       ChangeKind = "decoding"
+	ChangeDecoding ChangeKind = "decoding"
+	// ChangeInheritance records structural input expansion. It is inspection
+	// metadata, not an operation accepted by Resolution.Record.
+	ChangeInheritance    ChangeKind = "inheritance"
 	ChangeDerivedDefault ChangeKind = "derived_default"
 	ChangeNormalization  ChangeKind = "normalization"
 )
@@ -161,6 +164,11 @@ const (
 	CodeOverrideLimitExceeded Code = "override.limit_exceeded"
 
 	CodeExplainLimitExceeded Code = "explain.limit_exceeded"
+
+	CodeInheritanceInvalid Code = "inheritance.invalid"
+	CodeInheritanceMissing Code = "inheritance.missing"
+	CodeInheritanceCycle   Code = "inheritance.cycle"
+	CodeInheritanceVersion Code = "inheritance.version"
 )
 
 // Location identifies a position in a configuration source. Zero line and column
@@ -197,13 +205,23 @@ type Diagnostic struct {
 	Related  []Location
 }
 
+// InheritanceStep identifies a concrete payload transfer controlled by a
+// relationship directive. Locations belong to that directive, not its value.
+type InheritanceStep struct {
+	From      Path
+	To        Path
+	Reference Path
+	Locations []Location
+}
+
 // 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.
 type Origin struct {
-	Layer     Layer
-	Locations []Location
-	Operation ChangeKind
+	Layer       Layer
+	Locations   []Location
+	Operation   ChangeKind
+	Inheritance []InheritanceStep
 }
 
 // FieldInfo describes an effective configuration path.
@@ -257,6 +275,16 @@ func cloneSourceInfos(sources []SourceInfo) []SourceInfo {
 
 func cloneOrigin(origin Origin) Origin {
 	origin.Locations = cloneLocations(origin.Locations)
+	if origin.Inheritance != nil {
+		steps := make([]InheritanceStep, len(origin.Inheritance))
+		for index, step := range origin.Inheritance {
+			steps[index] = InheritanceStep{
+				From: step.From.clone(), To: step.To.clone(), Reference: step.Reference.clone(),
+				Locations: cloneLocations(step.Locations),
+			}
+		}
+		origin.Inheritance = steps
+	}
 	return origin
 }