Thanks to everyone who has given suggestions for how to fix this. Unfortunately most of them require me standing up for longer than I can manage, so I've mainly just fiddled with settings (since I can do that from my bed).

but when I can, I'll be:
* calibrating the extruder
* trying to clear clogs in the hot-end
* calibrating the z-axis offset (which is a multistep nightmare in this setup)

installed a USB power blocker to try and fix the undervolting. it didn't work.

So I'm gonna have to find another power supply for that

okay I tried switching to a different USB power supply (5v 2A) with thicker usb cables: No difference, still undervolting.

I also cold-pulled the hot end a few times, to see if that'll help.

Seems pretty good.

My z-alignment is still fucked. I printed this on a raft because I knew it still was, but the raft was nearly impossible to remove. it was WELDED to the build plate.

and keep in mind that's me saying it as someone who has made it their livelong profession and hobby of touching computers as much as they can. I love a bunch of little places to change things. I love being able to fiddle with settings.

3d printing has too many settings

fiddled with my z-offset calibration. tried measuring the build plate: that was a mistake. The thing is bent as fuck.

but it does do a 4x4 grid for level so maybe it can compensate enough for that to not be a huge problem. Lets see, time for another 9 hour print!

Okay I thought I fixed the clog and turned up the print temp and did another Calicat. At the end of the print, the webcam showed nothing there. I watched the time-lapse, and yep. No filament at all came out.

So I've got something way more broken than just a low temperature

the Principle of What Changed, however, says it's the filament:
I printed like 10 CHEP cubes and CaliCats in the last couple weeks, zero spaghetti.

I switch to the green filament, everything I've printed is spaghetti.

Got some fresh filament, it printed a CaliCat just fine at 200°C.
I also swapped to a Pi4 for OctoPrint, so no more undervoltage errors.

Now lets see if we can do a loooong print

new filament failed. I went in there and the extruder was clicking, trying and failing to shove plastic through the hot end.

SO YEAH I KINDA HATE THIS THING