Function detect_runner 

pub fn detect_runner(
    config: &Config,
    reporter: &dyn Reporter,
) -> Result<Runner, DeployError>

Detect which runtime this project uses: Next.js, Rails, Rust, Swift, or a build-less static site.

The detection itself lives in Runner::from; this wraps it with progress reporting and the monorepo short-circuit. It owns no spinner and prints nothing directly. All progress goes through reporter, so the same call works under the CLI, in CI, or on the server.