Add a project-root conftest.py that snapshots `git status --porcelain -- tests/fixtures/` at pytest_sessionstart and diffs at pytest_sessionfinish. Any new or modified entry relative to the session baseline fails the session with a named-path stderr message and a 3-5 line guidance block pointing at journal_copy, the _SOLSTONE_JOURNAL_OVERRIDE env var, and mocking. Silent on clean sessions; emits a single-line skip warning when git is unavailable or the working tree is not a repo. Motivated by two prior fixture-leak incidents: - f6f382a6 (supervisor schedule tests spawning sol dream and writing into chronicle/<date>/health/) - 2996e072 (test_api_baselines per-test autouse clobbering the isolated override) Both classes of bug would have been caught at session end by this detector before landing in a commit. Covers both pytest entry points (`pytest tests/ --ignore=tests/integration` from `make test` and `pytest apps/` from `make test-apps`) because pytest walks from the rootdir (project root, anchored by pyproject.toml) and loads the top-level conftest.py for both. Ships with a pytester-based canary at tests/test_fixture_leak_detector.py that spins up miniature nested pytest sessions in isolated tmp dirs (with explicit --basetemp to avoid colliding with the repo's --basetemp=/var/tmp/pytest-solstone) and verifies: (a) the detector fires and names a leaked path, (b) stays silent on a clean session, (c) emits the skip warning outside a git repo. tests/conftest.py's set_test_journal_path default (still tests/fixtures/ journal) is deliberately unchanged — flipping that default is a separate scope. This lode observes, it does not prevent. Signed-off-by: Jer Miller <jeremie.miller@gmail.com>