Replay added configuration paths in explanations

explain.go

@@ -134,7 +134,7 @@ func (r *Result[T]) Explain(path Path) (Explanation, bool) {
 	}
 
 	working = document.Clone(r.input)
-	for _, snapshot := range r.resolution {
+	for _, snapshot := range coalescedResolutionSnapshots(r.resolution) {
 		relevant := pathsIntersect(snapshot.change.Path, path)
 		var before ValueSnapshot
 		if relevant {
@@ -271,6 +271,37 @@ func mergeHistoryAtPath(root **document.Node, path Path, incoming *document.Node
 	}
 }
 
+// Resolution records describe one before/final transformation, not assignment
+// order. A parent already carries its descendants' final values; merge overlapping
+// intent into that event rather than replay a child assignment a second time.
+func coalescedResolutionSnapshots(snapshots []resolutionSnapshot) []resolutionSnapshot {
+	groups := make([]resolutionSnapshot, 0, len(snapshots))
+	for _, snapshot := range snapshots {
+		merged := false
+		for i := range groups {
+			if !pathContains(groups[i].change.Path, snapshot.change.Path) {
+				continue
+			}
+			for _, reason := range snapshot.change.Reasons {
+				groups[i].change.Reasons = appendUniqueString(groups[i].change.Reasons, reason)
+			}
+			for _, dependency := range snapshot.change.Dependencies {
+				groups[i].change.Dependencies = appendUniquePath(groups[i].change.Dependencies, dependency)
+			}
+			if snapshot.change.Origin.Operation == ChangeNormalization {
+				groups[i].change.Origin.Operation = ChangeNormalization
+			}
+			merged = true
+			break
+		}
+		if !merged {
+			snapshot.change = cloneChange(snapshot.change)
+			groups = append(groups, snapshot)
+		}
+	}
+	return groups
+}
+
 func replaceHistoryPath(root **document.Node, path Path, replacement *document.Node) {
 	if root == nil || *root == nil {
 		return
@@ -289,7 +320,19 @@ func replaceHistoryPath(root **document.Node, path Path, replacement *document.N
 			}
 			position := documentEntryIndex(current.Mapping, segment.key)
 			if position < 0 {
-				return
+				if replacement == nil {
+					return
+				}
+				child := &document.Node{Kind: document.Mapping}
+				if last {
+					child = document.Clone(replacement)
+				}
+				current.Mapping = append(current.Mapping, document.Entry{Key: segment.key, Value: child})
+				if last {
+					return
+				}
+				current = child
+				continue
 			}
 			if last {
 				if replacement == nil {