Theoretically, none of that unlocking stuff should matter. Firehose should be OS agnostic and not know anything about that stuff.
It surprising that both the GoCo7 and Go103 with different flash types have the same problem.
So to recap (please correct me):
Writing a partition with EDL freezes when it tries to write.
Normal bootloader fastboot has had the commands ripped out of it.
(Whether this is Onyx being mean or just the migration to fastbootd, I don't know.)
Recovery fastbootd accepts commands but fails on write.
I've been doing some reverse engineering on this Firehose loader.
It really shouldn't freeze like that even for errors.
I've learned "many cheerful facts about the square of the hypotenuse".
