Issue: I managed to correct a boot loop issue with a dead batter during an update, hopefully my experience will save someone else some stress. Last night I forgot to charge my Pixel 7 with a pending update, which lead to unexpected behavior. While the phone was charging using a Google branded cable and power brick (45 watts?), the phone would rotate between the Google/GrapheneOS splash screens and the "you're loading another OS" scare screen, the behavior was identical using a car charger of similar quality during my two hour commute. Pressing/holding any button/buttons in any combination had no effect.
Solution: Unplugged phone for roughly two hours so the battery would die completely, charged it using a Lenovo branded 65 watt laptop charger for roughly five minutes, pressed the phone's power button during the scare screen. This ended the boot loop with my Pixel 7 displaying a battery percentage of 2%.
I have no idea why this worked, hopefully someone smarter than I am can dissect this experience and use it to help someone else.