title: Thread a new option through several files
check: python -m pytest -q .bench_check
plan: |
  Milestone 1: add a --shout option to the greeter.

  1. In `greeter/core.py`, give `greet` a keyword argument `shout: bool = False`.
     When it is true, return the whole greeting in upper case:
     greet("Bob", shout=True) == "HELLO, BOB!". The default behaviour is unchanged.
  2. In `greeter/cli.py`, add a `--shout` flag (action="store_true") and pass it
     to `greet`.
  3. Add two tests to `tests/test_greeter.py`: one for greet with shout=True, and
     one that calls `main(["--shout", "Bob"])` and checks the printed output
     using pytest's capsys fixture.
  4. Run `python -m pytest -q` until every test passes, and check that
     `python -m greeter --shout Bob` prints `HELLO, BOB!`.
  5. Call finish_milestone, with final yes.