anyway, my phone turned itself off when i started exploring further, and started bootlooping.
during one of the first few boots it mismounted my sd card, instead mounting an old hidden partition i had from a previous flash of the phone. i had written the previous image’s encryption key into the hidden partition, and this file was displayed to me in the file manager when i went to look what was wrong with the sd card, i don’t remember how to mount that partition manually.
the bootloop was because there were so many directories on the sd card that it wouldn't complete fsck before a system watchdog expired. the hidden partition was not mounted; it was the normal partition, remounting. i'd forgotten the key was on the root folder; i must rarely use the files view. i don't why it remounted, but it was mostly coincidence that this was the first moment it remounted since the watchdog threshold regarding number of directories was reached.