Function try_run_standalone 

pub fn try_run_standalone(
    argv: &[String],
) -> Option<Result<(), Box<dyn Error + Send + Sync>>>

If argv names a project-independent built-in, run it and return Some(result). Return None otherwise, so the caller (the global umbral binary) forwards the command to the project via cargo run.

This is what lets umbral maskkeygen work anywhere — including outside a project — without a build, while umbral migrate / umbral seed_data still forward to the compiled project that actually owns those commands.