> Unlike dlopen-based plugin systems, threadprocs run traditional executables with a `main()` function.

Why not dlopen with something that calls plugin_main() (etc.) in its own thread?

Good call-out, and I think that's a more practical approach for most systems.

For this project, one of my goals was to impose the fewest dependencies possible on the loaded executables, and give the illusion that they're running in a fully independent process, with their own stdin/out/err and global runtime resources.

  "./my_prog abc" -> "launcher s.sock ./my_prog abc"