ember-data belongsTo proxy unresolved REPL

adapters.application.js

import EmberObject from '@ember/object';
import { resolve } from 'rsvp';

export default class ApplicationAdapter extends EmberObject {
  findRecord() {
    return resolve({
      data: {
        type: 'parent',
        id: '1',
        attributes: {
          name: 'John'
        },
        relationships: {
          children: {
            data: [
              { type: 'child', id: '1' },
              { type: 'child', id: '2' }
            ]
          }
        }
      },
      included: [
        {
          type: 'child',
          id: '1',
          attributes: {
            name: 'Chris'
          },
        },
        {
          type: 'child',
          id: '2',
          attributes: {
            name: 'Jim'
          },
        }
      ]
    });
  }
}

models.child.js

import Model from 'ember-data/model';
import attr from 'ember-data/attr';
import { belongsTo, hasMany } from 'ember-data/relationships';

export default Model.extend({
  name: attr(),
  parent: belongsTo('parent', {
    async: false,
    inverse: 'children'
  })
});

models.parent.js

import Model from 'ember-data/model';
import attr from 'ember-data/attr';
import { belongsTo, hasMany } from 'ember-data/relationships';

export default Model.extend({
  name: attr(),
  children: hasMany('child', {
    // it does not matter whether this is true or false
    async: false, 
    inverse: 'parent'
  })
});

routes.application.js

import Route from '@ember/routing/route';

export default Route.extend({
  model() {
    return this.get('store').findRecord('parent', '1');
  },
  actions: {
    checkInJs(child) {
      console.log({
        child,
        dotParent: child.parent,
        getParent: child.get('parent')
      });
    }
  }
});

serializers.application.js

export default class ApplicationSerializer {
  constructor(config) {
    Object.assign(this, config);
  }
  static create(config) {
    return new this(config);
  }
  normalizeResponse(_, __, data) { return data; }
}

templates.application.hbs

<ul>
  {{#each model.children as |child|}}
    <li>
      <i>{{child.name}}</i>
      <b>has parent</b>
      <u>{{child.parent.name}}</u>
      <br><br>
      Status: <button {{action "checkInJs" child}}>Log Me</button><br>
      {{#if child.parent._belongsToState}}
      <ul>
        <li>Has Content:
          <b>{{if child.parent.content 'true' 'false'}}</b>
        </li>
        <li>Has Promise:
          <b>{{if child.parent.promise 'true' 'false'}}</b>
        </li>
        <li>Fulfilled:
          <b>{{if child.parent.isFulfilled 'true' 'false'}}</b>
        </li>
        <li>Pending:
          <b>{{if child.parent.isPending 'true' 'false'}}</b>
        </li>
        <li>Settled:
          <b>{{if child.parent.isSettled 'true' 'false'}}</b>
        </li>
        <li>Rejected:
          <b>{{if child.parent.isRejected 'true' 'false'}}</b>
        </li>
        <li>Truthy:
          <b>{{if child.parent.isTruthy 'true' 'false'}}</b>
        </li>
      </ul>
      <br>
      <i>This relationship is a proxy.</i><br><span style="font-size: .75em">Change the 'parent' relationship on the 'child' model to "async: false" to make it the record.</span>
      {{else}}
      <i>This relationship is not a proxy.</i><br><span style="font-size: .75em">Change the 'parent' relationship on the 'child' model to "async: true" to make it a proxy.</span>
      {{/if}}
      <hr>
    </li>
  {{else}}
    <li>No Children!</li>
  {{/each}}
</ul>

twiddle.json

{
  "version": "0.15.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "ENV": {},
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.4.3",
    "ember-template-compiler": "3.4.3",
    "ember-testing": "3.4.3"
  },
  "addons": {
    "ember-data": "3.7.0"
  }
}