fix(datasource/graphene) swap selected layer when activating merge tool

src/datasource/graphene/frontend.ts

@@ -1123,7 +1123,7 @@ class GraphConnection extends SegmentationGraphSourceConnection {
     annotationLayerStates.push(redGroup, blueGroup);
 
     if (layer.tool.value instanceof MergeSegmentsPlaceLineTool) {
-      layer.tool.value = undefined;
+      layer.tool.value = undefined; // unset the line tool if it is active when page is loaded
     }
 
     this.mergeAnnotationState = makeColoredAnnotationState(
@@ -2394,18 +2394,29 @@ class MergeSegmentsTool extends LayerTool<SegmentationUserLayer> {
       return;
     const {
       state: { mergeState },
+      mergeAnnotationState,
     } = graphConnection;
-    if (mergeState === undefined) return;
-    const { merges, autoSubmit } = mergeState;
-
     const lineTool = new MergeSegmentsPlaceLineTool(
       this.layer,
-      graphConnection.mergeAnnotationState,
+      mergeAnnotationState,
     );
+    // Switch selected layer to the layer associated with the tool
+    // to enable to place line tool. Swap back when deactivating.
+    const { selectedLayer, selectionState } = this.layer.manager.root;
+    const previousSelectedLayer = selectedLayer.layer;
+    const previousSelectedLayerVisible = selectedLayer.visible;
+    const previousTool = tool.value;
+    selectedLayer.layer = this.layer.managedLayer;
+    selectedLayer.visible = true;
     tool.value = lineTool;
+    const prevousSelectionState = selectionState.toJSON();
     activation.registerDisposer(() => {
-      tool.value = undefined;
+      selectedLayer.layer = previousSelectedLayer;
+      selectedLayer.visible = previousSelectedLayerVisible;
+      tool.value = previousTool;
+      selectionState.restoreState(prevousSelectionState);
     });
+    const { merges, autoSubmit } = mergeState;
     const { body, header } =
       makeToolActivationStatusMessageWithHeader(activation);
     header.textContent = "Merge segments";