Index stable history trees during normalization

internal/engine/history_source_test.go

@@ -77,18 +77,6 @@ func TestHistorySourceObservationsPreserveRawAndCompositeDefinitions(t *testing.
 	if composite == nil || !reflect.DeepEqual(locationSourceIDs(composite.origin.Locations), []string{"base", "overlay"}) {
 		t.Fatalf("empty mapping composite attribution = %#v; selections %#v", composite, emptySelections)
 	}
-	var emptySummary *historySourcePayload
-	for index := range model.sourcePayloads {
-		payload := &model.sourcePayloads[index]
-		if payload.kind == historySourceSummaryPayload && sameConcreteHistoryPath(payload.path, Keys("section", "empty")) {
-			emptySummary = payload
-			break
-		}
-	}
-	if emptySummary == nil || len(emptySummary.contributions) != 2 || emptySummary.contributions[0].id != 0 || emptySummary.contributions[1].id != 1 {
-		t.Fatalf("empty mapping summary contribution references = %#v", emptySummary)
-	}
-
 	metadata := Metadata{historyModel: model}
 	metadataHistory := metadata.History(Keys("section", "empty"))
 	var compositeSources []string