[AnimalMuppet]

The machine that packs your milk isn't produced by the dairy, and the machine that makes circuit boards isn't made by the company that makes circuit boards. They are produced by companies that makes those machines. These machines are a subset of "embedded systems". I regularly see job postings for such jobs (not on HN, but places like Indeed). This is often C++ programming, but there may be some Rust or Ada or straight C (even some assembly).

Supporting the supply chain is different. I'm sure there's a term for this area. (ERP, maybe? Does that fit?) I think a lot of this is Java coding, with (often) SQL on the back end. Again, though, the dairy or whatever doesn't usually write that software. They buy it, either from an ERP vendor or a consultancy. And again, yes, those jobs do appear, though perhaps using different words than you are expecting.