So the PCB's showed up, and everything soldered up perfectly the first time, so that's good.  Circuit works, and I was able to throw simple ESPHome code at it and make it function.  All that was easy and perfect...

But then, I went to test it in the real world, and that's when things were less than ideal.

Right now I have one cartridge fully used, and one fully new.  I put the sensors in the 3d-printed clips, attached, and the readings were garbage.  Same on both, or close enough to same that it didn't matter.  If I swapped the sensors around I just ended up with the same value over and over, or indistinguishable differences....

But this totally worked when I taped the sensors.  So I tried that again just for sanity, yep, taped sensors right to the cartridge, and it works.

My next thought was that I have the sensors too far from the cart now.  I have a 1cm tube the sensor shines down in the holder, and maybe that's too long, so I shortened it to about 1mm.  Still no good.

Right now my current thinking is that the black PLA is messing up the readings.  I would have thought black was the way to go, but maybe not.  I've just re-printed in cool white PLA, going to try that and see if I get different results... here's hoping.  I know this works, I just have to figure out how to mount it now.