ember-data-model-fragments: [Bug Ember 3.15.0+] Creating a tracked model with a fragment array throws back-tracking assertions

I’m currently trying to upgrade our app from ember-source 3.14.x to 3.15.x and I’ve found a blocker which is preventing our upgrade.

From ember-source 3.15.0-beta.4 it appears that tracked models which have properties using fragmentArray will throw a backtracking rerender assertion causing things to blow up.

There are two suspect commits in ember-source where this was introduced.

emberjs/ember.js#17834 [BUGFIX] Prevents autotracking ArrayProxy creation emberjs/ember.js#18554 [BREAKING BUGFIX] Adds autotracking transaction

I’ve created an extremely simplified test case in https://github.com/lytics/ember-data-model-fragments/pull/358 and it throws the following assertion:

Error: Assertion Failed: You attempted to update `[]` on `Array`, but it had already been used previously in the same computation.  Attempting to update a value after using it in a computation can cause logical errors, infinite revalidation bugs, and performance issues, and is not supported.

`[]` was first used:

- While rendering:
  
  application
    index
      my-component
        this.record

Stack trace for the first usage: 
    at get (http://localhost:7357/assets/vendor.js:14851:32)
    at Class._addArrangedContentArrayObserver (http://localhost:7357/assets/vendor.js:28971:44)
    at Class.init (http://localhost:7357/assets/vendor.js:28831:12)
    at Class.init (http://localhost:7357/assets/vendor.js:87960:12)
    at Class.superWrapper [as init] (http://localhost:7357/assets/vendor.js:30845:22)
    at initialize (http://localhost:7357/assets/vendor.js:29137:9)
    at Function.create (http://localhost:7357/assets/vendor.js:29720:9)
    at createFragmentArray (http://localhost:7357/assets/vendor.js:88297:32)

Stack trace for the update:
    at dirtyTagFor (http://localhost:7357/assets/vendor.js:55641:11)
    at markObjectAsDirty (http://localhost:7357/assets/vendor.js:14006:32)
    at notifyPropertyChange (http://localhost:7357/assets/vendor.js:14043:5)
    at arrayContentDidChange (http://localhost:7357/assets/vendor.js:14144:7)
    at replaceInNativeArray (http://localhost:7357/assets/vendor.js:14210:5)
    at Array.replace (http://localhost:7357/assets/vendor.js:27255:39)
    at Class.setupData (http://localhost:7357/assets/vendor.js:88000:15)

The problem appears to happen in the following lines, specifically 298 (where the array is created) and 300 (where the array is updated) https://github.com/lytics/ember-data-model-fragments/blob/c00e2b1a40b296e0c0c3c21ca0f463d12888cd27/addon/attributes.js#L298-L300

The array is first set up in createArray at

https://github.com/lytics/ember-data-model-fragments/blob/c00e2b1a40b296e0c0c3c21ca0f463d12888cd27/addon/attributes.js#L195-L208

the array is modified a second time in

https://github.com/lytics/ember-data-model-fragments/blob/f1c7060fb7560aaea26760e0270234823b9e20db/addon/array/stateful.js#L79

While in my test reproduction I am specifically marking the property as @tracked

@tracked selectedRecord = this.store.createRecord('my-model', { fragments: [] });