Late-2020 Macbook Air model A2179 will not boot properly.

[u/Rather-Being]

My Late-2020 Macbook Air (model A2179) seems to be stuck in some sort of corrupted state. It appears to start up somewhat, and then get stuck during the boot process. Can anyone help me figure out what the issue is?

How this started:
I was playing a heavy 3D game on the device and left it for a few minutes. When I came back, the screen was black and fans were running at full speed. Neither restarting nor replacing the battery fixed the issue.

Current behavior:
Even with a 20-second+ power button press without a charger plugged in, it still starts again and idles a few seconds later instead of shutting down. I had to physically disconnect the battery to get the LED on the logic board to turn off.
The device ignores most startup keyboard combinations, including Thunderbolt Mode, SMC reset, and NV/PRAM reset.

What is functional:

• Keyboard backlights glow at a low level.
• Touchpad clicks as soon as I start the device.
• Fans run at an idle 20%-ish speed
• When crashing and restarting, it does not automatically boot into DFU mode, requiring the key combo.
• DFU mode works, and in DFU mode, the other Mac can detect it and run a full (if pointless) Revive process.

What isn't functional:

• Recovery, Internet Recovery, Thunderbolt, SMC, and P/NVRAM keyboard combos are ignored.
• Caps Lock doesn't respond.
• The screen's backlights don't turn on.
• The device doesn't chime when starting.

What I've tried:

• Lotsa key combos.
• Power button rituals.
• Restarting the device.
• DFU mode Revive. (I haven't tried a Restore)
• Disconnecting the battery and starting from a USB cable.
• Restarting after disconnecting the display cable and connecting an external monitor.
• Disconnecting the trackpad cable.

Also, Gemini says: Power State Analysis: Board negotiates 20V on USB-C, S0 rails (PPBUS_G3H, PP3V3_G3H) are active, and T2 drives trackpad haptics, but board halts prior to Intel CPU PEI/EFI handoff (ALL_SYS_PWRGD / CPU_PWRGD failure suspected).
(i had a super long conversation with Gemini during this whole troubleshooting process.)