Integrate history prefixes into load handoffs

internal/engine/metadata.go

@@ -13,6 +13,16 @@ type Metadata struct {
 	historyModel   *historyModel
 }
 
+func (m Metadata) currentHistoryModel() *historyModel {
+	if m.historyModel != nil {
+		return m.historyModel
+	}
+	if m.historyBuilder != nil {
+		return m.historyBuilder.model
+	}
+	return nil
+}
+
 // Lookup returns information for an effective path. Unknown and invalid paths
 // return false.
 func (m Metadata) Lookup(path Path) (FieldInfo, bool) {
@@ -152,6 +162,21 @@ func finalizeMetadataPaths(m *Metadata, final *document.Node, applications []his
 func finalizeMetadataPathsWithResolution(m *Metadata, final *document.Node, applications []historyApplication, snapshots []resolutionSnapshot, earlier ...*document.Node) {
 	finalizeEffectiveMetadataPaths(m, final)
 	builder := m.historyBuilder
+	if builder != nil && builder.prefixReady {
+		if len(snapshots) != 0 && builder.model.resolutionPayload == nil {
+			if len(earlier) != 0 {
+				builder.setScratch(earlier[len(earlier)-1])
+			}
+			builder.observeResolutionEvidence(snapshots)
+		}
+		if builder.model.final != final {
+			builder.model.final = final
+			builder.registerDocumentRoot(final)
+		}
+		m.historyModel = builder.freeze()
+		m.historyBuilder = nil
+		return
+	}
 	if builder == nil {
 		builder = newHistoryBuilder()
 	}