Validate source equivalence and layered scaling

internal/engine/load_request.go

@@ -126,6 +126,7 @@ func assembleLayeredInput[T any](request loadRequest[T], input assembledInput, a
 }
 
 func acquireUnderlayGroup(group loadGroup, index int, rule *VersionRule, accounting *importAccounting) (*composedDocument, []SourceInfo, map[string]ResourceContext, []Diagnostic) {
+	initialBytes, initialNodes := accounting.bytes, accounting.nodes
 	visited := make(map[resourceIdentity]importRoute)
 	hostToken := &namespaceToken{}
 	var documents []*document.Node
@@ -168,6 +169,8 @@ func acquireUnderlayGroup(group loadGroup, index int, rule *VersionRule, account
 	if len(diagnostics) != 0 {
 		return nil, sources, contexts, diagnostics
 	}
+	composition.inputBytes = accounting.bytes - initialBytes
+	composition.inputNodes = accounting.nodes - initialNodes
 	for pointer, origin := range composition.origins {
 		origin.Layer = LayerUnderlay
 		composition.origins[pointer] = origin