Cut metadata history over to shared model

internal/engine/history_source.go

@@ -33,6 +33,7 @@ func (builder *historyBuilder) observeBaseline(root *document.Node) {
 		return
 	}
 	builder.model.baseline = root
+	builder.registerDocumentRoot(root)
 	payload := builder.nextPayload(historyPhaseBaseline)
 	defaultAttribution := builder.addAttribution(Origin{Layer: LayerDefault}, nil, nil)
 	walkDocument(root, Path{}, func(path Path, node *document.Node) {
@@ -69,6 +70,17 @@ func (builder *historyBuilder) observeSourceEvidence(root *document.Node, origin
 	for index := range records {
 		record := records[index]
 		payload := builder.addSourcePayload(nil, &record)
+		for displacedIndex, displaced := range record.displaced {
+			definitionPayload := payload
+			definitionPayload.substep = displacedIndex + 1
+			definition := builder.addAttribution(displaced.origin, nil, nil)
+			builder.addObservation(historyObservation{
+				path: displaced.path, phase: historyPhaseSources, payload: definitionPayload,
+				reportedPath: displaced.path, role: historyRoleDefinition,
+				beforePresent:  true,
+				attributionRef: definition,
+			})
+		}
 		attribution := builder.addAttribution(record.change.Origin, nil, nil)
 		for _, displaced := range record.displaced {
 			builder.addObservation(historyObservation{