"""Unit test package.

Like ``tests/e2e/``, this directory is a package so its test modules
import as ``unit.<name>`` instead of a top-level ``<name>``: a
same-basename file in two collected directories (phase 82 ships
``test_security_headers.py`` in BOTH this directory and
``tests/integration/``) makes pytest's default import mode raise an
"import file mismatch" on the full suite. ``tests/integration/`` stays a
plain directory on purpose — several of its files use sibling imports
(``from test_chat_api import …``), which require top-level module names.
"""