Add captured configuration comparison

internal/configuration/inspection.go

@@ -16,6 +16,15 @@ type Inspection interface {
 	Explain(configkit.Path) (configkit.Explanation, bool)
 	WriteEffective(io.Writer) error
 	WriteExplanation(io.Writer, configkit.Path) error
+	capturedResult() *configkit.Result[document]
+}
+
+type inspectionResult struct {
+	*configkit.Result[document]
+}
+
+func (inspection inspectionResult) capturedResult() *configkit.Result[document] {
+	return inspection.Result
 }
 
 // Inspection returns only the retained result's inspection operations.
@@ -23,7 +32,19 @@ func (state *loaded) Inspection() Inspection {
 	if state == nil {
 		return nil
 	}
-	return state.result
+	return inspectionResult{Result: state.result}
+}
+
+// Diff compares two captured ConfigKit results without reconstructing them.
+func Diff(left, right Inspection) ([]configkit.Difference, error) {
+	var leftResult, rightResult *configkit.Result[document]
+	if left != nil {
+		leftResult = left.capturedResult()
+	}
+	if right != nil {
+		rightResult = right.capturedResult()
+	}
+	return configkit.Diff(leftResult, rightResult)
 }
 
 func secretProviderPath(path configkit.Path) bool {