Developer feedback: "Rust is so much better in this regard, I couldn't get Free Pascal to build my old code on Linux. So I rewrote it in Rust."
Reality: Developer installed the wrong Debian package, resulting a partial Free Pascal Compiler setup, that lacked the package needed for the build.
Solution: Installed the correct package. Build is immediately fixed.
Takeaway: If you try hard enough, you can even fix missing Debian packages with Rust. But you probably shouldn't.