[thorwhalen]

Summary

• rtmlib 0.0.16 declares opencv-python and opencv-contrib-python unconditionally (no marker), and its only cv2 usage is plain-API (VideoCapture, dnn.readNetFromONNX, drawing helpers — nothing contrib-only), confirmed by extracting the wheel and grepping its source.
• Measured that a pyproject constraint alone cannot make paces[media,pose]'s closure single-provider: pip/uv have no per-transitive-dependency exclusion for a requirement a third-party package declares unconditionally. --no-deps on rtmlib itself works (it only needs onnxruntime/tqdm beyond cv2, both easy to add back), but there's no way to express "exclude just opencv-python" as a pyproject.toml constraint without forking rtmlib.
• So the fix here is the honest one named in the issue: a documented two-step install recipe (README) that keeps the closure single-provider, plus check_pose_requirements() now names the repair command (not just the collision) when both providers are already present, with a test that forces that branch deterministically via monkeypatch (doesn't depend on the local environment's actual installed set).

Measurement (read-only, commands used)

# which cv2 wins today, and who else claims its files
python -c "import cv2; print(cv2.__file__, cv2.__version__)"
pip show -f opencv-python opencv-contrib-python | grep "cv2/__init__.py"

# mixing's pinned single provider
grep -n opencv <mixing repo>/pyproject.toml

# rtmlib's actual declared deps + resolved closure (no install)
uv pip compile <(echo "rtmlib>=0.0.16,<0.1")

# rtmlib's cv2 usage, from the wheel itself (no install into the env)
pip download --no-deps --dest <tmp> "rtmlib>=0.0.16,<0.1"
python -m zipfile -e rtmlib-*.whl <tmp>/extracted/
grep -rn "cv2\." <tmp>/extracted --include="*.py"

Confirmed: both opencv-python and opencv-contrib-python list cv2/__init__.py in their RECORD, so whichever installs last wins and uninstalling either can leave the survivor's cv2 with missing files — exactly the failure check_pose_requirements() now names a repair for.

Test plan

• pytest tests/test_pose.py -q — 32 passed, 1 skipped
• pytest -q (full suite) — 218 passed, 1 skipped
• ruff check paces/pose.py tests/test_pose.py — clean
• new test forces the two-provider branch via monkeypatch on importlib.metadata.version, independent of what's actually installed locally

Closes #20

https://claude.ai/code/session_016W3RcNo6snhKTw44jP6QWb