Tolino Shine 5 to Kobo Software Issues

[vinnistinni]

The Tolino Shine 5 bricked during conversion to Kobo firmware. It is stuck in a reboot loop but the recovery partition runs and completes fine, but it just reapplies the same broken state every time.

The device briefly appears over USB during each boot cycle as a Mass Storage Gadget (VID 0525 / PID a4a5), but disconnects before the kernel creates a block device node. I watched it with udevadm monitor for several cycles, USB and SCSI host events show up, but there is no block device, so there is nothing to mount. I tried a udev rule targeting block add events, but it never fires for obvious reasons.

At this point, I'm not sure what to do next. I have a few questions that I hope someone here might be able to answer:

Is BROM or preloader mode reachable on the Shine 5 at all over USB?
Are there any known test points for the MT8113L on this board?
Is there a scatter file for this model for SP Flash Tool anywhere?
Is there any other way to get a file onto the device in this state that I'm missing?

I'm happy to share the full dmesg output if it would be useful.
Disclaimer: I used AI trying to get the device back into a working state and also in drafting the questions because I am way in over my head.
I‘d be very grateful for any kind of help!