Function run 

pub fn run(
    tb: &dyn Toolbox,
    compiler: &Compiler,
    project_root: &Path,
    src_rel: &Path,
    node_floor: u32,
    opts: &DevOptions,
) -> ExitCode

Orchestrate a local dev session: pre-flight, compile, select the worker, and hand off to wrangler dev. Returns wrangler’s own exit code on a clean hand-off, or a pre-flight/build failure code before serving.