How to disable midpoint selection, dragging for LineString types (draw_line_string mode)

How do I disable the ability for a user to select (direct_select) the midpoint of a LineString in mapbox-gl-draw? I have a custom mode for "annotations", which should only allow for LineStrings with 2 vertices.

I've tried some of the lifecycle hooks in custom modes (https://github.com/mapbox/mapbox-gl-draw/blob/master/docs/MODES.md), specifically for draw_line_string, including onDrag. My problem is I don't want the drag point to exist at all (it would involve the user seeing a midpoint, dragging that vertex, and then seeing it snap back).

I've also tried dealing with the draw styles, but they are general to all midpoints (include polygons).

A third way might be to invalidate this outside of mapbox-gl-draw, in my framework, but I'd like to avoid even the ability to select a midpoint at all.

You can achieve that by creating a custom mode from direct_select mode:

import * as MapboxDraw from '@mapbox/mapbox-gl-draw/dist/mapbox-gl-draw';
import createSupplementaryPoints from '@mapbox/mapbox-gl-draw/src/lib/create_supplementary_points';
import Constants from '@mapbox/mapbox-gl-draw/src/constants';

const DirectSelectWithoutMiddleVertexMode = MapboxDraw.modes.direct_select;

DirectSelectWithoutMiddleVertexMode.toDisplayFeatures = function (state, geojson, push) {
  if (state.featureId === geojson.properties.id) {
    geojson.properties.active = Constants.activeStates.ACTIVE;
    push(geojson);
    createSupplementaryPoints(geojson, {
      map: this.map,
      midpoints: false,
      selectedPaths: state.selectedCoordPaths
    }).forEach(push);
  } else {
    geojson.properties.active = Constants.activeStates.INACTIVE;
    push(geojson);
  }
  this.fireActionable(state);
};

export default DirectSelectWithoutMiddleVertexMode;

The only thing to do is to set the midpoints property to false that avoids the midpoint creation.

After that, use the custom mode to override direct_select mode in the draw options :

import DirectSelectWithoutMiddleVertexMode from './DirectSelectWithoutMiddleVertexMode';

const drawOptions = {
    modes: Object.assign({
        direct_select: DirectSelectWithoutMiddleVertexMode
    }, MapboxDraw.modes)
};

const draw = new MapboxDraw(drawOptions);