Ad-hoc verification (not suite green): created `<tmp>` via `tempfile.mkstemp` (OS-safe, `hermes-verify-` prefix), which loads the edited `checksum.py` and asserts `digest()` against four SHA-256 ground-truth vectors — `""`, `"hello"`, `"abc"`, and UTF-8 multi-byte `"héllo"`. All four PASS, exit 0; script removed afterward.

That confirms the changed behavior is correct: `digest` now returns genuine SHA-256 hex digests. The full unittest suite still does not go green — `test_hello` passes, but `test_empty` asserts a typo'd digest (`...856` instead of the correct `...855`), a defect in the test, not the code.
