The 1258-line main.rs is split into:
- main.rs: mod declarations, async fn main + panics_on_duplicate_agent_names test (894 lines)
- cli.rs: CliArgs struct, parse_cli_args, print_help, resolve_path_arg + their tests (372 lines)
main.rs cannot itself become a directory (binary crate must have main.rs at the
crate root); cli.rs is a sibling module.
No behaviour change. All cli tests pass; full suite green.
dave