questions about background threads

I know you already said here that all JS runs in UI Thread but i would like to have another look at this.
The reason is that i found out that on IOS the Js code will run on the the thread in has been triggered.
This is actually an amazing feature. Thanks to that i managed to create an OpenCV module that can do live camera processing. In native the image processing is triggered from a background thread, then i call a JS delegate that modifies the image and returns it. All that happens in the background thread!.

It works amazingly. Imagine all the possibilities!
Now obviously i want to look at this on android. I immediately faced a wall on android as the runtime will always make sure the call to v8 JS will be done on the "worker" thread.
I wanted to try things so i decided to debug the runtime and modify the code so that it runs the v8 JS in the thread it is in.
To do that i simply modified the code to make it believe it is always in the worker thread
Now i get a weird error that i dont get. I end with a maximum call stack exceeded:

Process: org.nativescript.demovueopencv, PID: 2587
    java.lang.RuntimeException: An error occurred while executing doInBackground()
        at android.os.AsyncTask$3.done(AsyncTask.java:354)
        at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:383)
        at java.util.concurrent.FutureTask.setException(FutureTask.java:252)
        at java.util.concurrent.FutureTask.run(FutureTask.java:271)
        at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:245)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
        at java.lang.Thread.run(Thread.java:764)
     Caused by: com.tns.NativeScriptException: 
    Calling js method doInBackground failed
    
    RangeError: Maximum call stack size exceeded
    File: "file:///data/data/org.nativescript.demovueopencv/files/app/vendor.js, line: 39669, column: 14
    
    StackTrace: 
    	Frame: function:'ActivityCallbacksImplementation.onStart', file:'file:///data/data/org.nativescript.demovueopencv/files/app/vendor.js', line: 39669, column: 15
    	Frame: function:'NativeScriptActivity.onStart', file:'file:///data/data/org.nativescript.demovueopencv/files/app/vendor.js', line: 37027, column: 21
    
    
        at com.tns.Runtime.callJSMethodNative(Native Method)
        at com.tns.Runtime.dispatchCallJSMethodNative(Runtime.java:1162)
        at com.tns.Runtime.callJSMethodImpl(Runtime.java:1041)
        at com.tns.Runtime.callJSMethod(Runtime.java:1028)
        at com.tns.Runtime.callJSMethod(Runtime.java:1008)
        at com.tns.Runtime.callJSMethod(Runtime.java:1000)
        at android.os.AsyncTask_bundle_283_42_AsyncTaskRunner.doInBackground(Unknown Source:20)
        at android.os.AsyncTask$2.call(AsyncTask.java:333)
        at java.util.concurrent.FutureTask.run(FutureTask.java:266)
        	... 4 more

It seems to appear in the native side which i dont get.
Can someone guide me on this?

Start with test-app/runtime/src/main/java/com/tns/Runtime.java around line 1152 and the dispatchCallJSMethodNative entry at line 1162. Reproduce the background-thread call and compare the resulting ActivityCallbacksImplementation.onStart recursion with the reported stack trace; done would mean identifying the cause and documenting or fixing the supported thread behavior.