Function build 

pub async fn build(
    project: &Project,
    launcher_dir: &Path,
    sccache_path: Option<PathBuf>,
    progress: Option<BuildProgress>,
) -> Result<PathBuf>

Build the launcher binary for the host and return its path.

The TUI launcher always builds the static-runtime variant: it is a leaf binary, not a plugin host, so the shared-runtime linkage has nothing to offer it.

Errors

Returns an error if the project’s target directory cannot be resolved or the Cargo build fails.