> To cut a disk you need to pack the grooves as close as possible.

Strictly speaking, the grooves only need to be cut as close as necessary in order for music to fit, while remaining far-enough apart that they don't interact too much.

Packing as many grooves (and thus as much material) as possible onto one side of a disk isn't always a goal, although it can be a goal.

> But the spiral isn't fixed, it's adjusted dynamically. Quiet sections can be packed close together.

Aye. Or the whole thing can be made quieter. Or dynamically-compressed first, and then made quieter. Or if it's a relatively short work, it can tolerate being louder and/or more-dynamic even though that takes up more physical space. There's lots of knobs here, and all of these knobs can be turned.

> That means that before cutting, the machine needs to know how much physical space it needs for the audio it's about to put on the disk.

That's not quite right. The process should ideally know this in advance, but that process can include a skilled human operator. And since we still have humans, it is not necessary for the machine itself to figure all of this out on its own.

Like many other kinds of machine work, a lot of it can be boiled down to some moral equivalent of speeds and feeds. There's a good chance that you've worked with this at home with a 3D printer by winding things up or down manually as a print progresses and observing the results. (Except: This is subtractive instead of additive, and we hear the results instead of seeing them.)

I see nothing that suggests that this record lathe can't be manually controlled. Instead, I see suggestion (based on the snippet about locked grooves being possible) that very fine, deliberate control is exactly what it is made to allow.

One can therefore add whatever knobs they want at whatever layer the combination of this device and one's skills permit, and send it. If the process fails, then learn from that and try again.

It's OK when it fails. Fucking things up is a time-honored tradition: At most stages of the recording/mixing/mastering/distribution process, it's pretty uncommon to one-shot anything.

Blank discs aren't necessarily expensive. It's OK to fuck them up.