[2Zest]

Closes #71940

Summary

Groupby and resample ohlc reductions on pyarrow-backed numeric arrays produce a two-dimensional masked result. The Arrow conversion helper attempted to construct a one-dimensional Arrow array from that result and raised ValueError: Mask must be 1D array.

Multi-output reductions now keep the delegated masked result so the data manager can split it into the four output columns. One-dimensional reductions continue to convert back to the original Arrow dtype.

Tests

• python -m compileall -q pandas/core/arrays/arrow/array.py pandas/tests/groupby/aggregate/test_aggregate.py
• python -m pytest pandas/tests/groupby/aggregate/test_aggregate.py -k test_ohlc_pyarrow_dtype -q (blocked locally because the in-place pandas extension module pandas._libs.pandas_parser is not built)
• git diff --check

I used OpenAI Codex to develop this pull request, reviewed and understood every change, and included the regression test.

• closes BUG: groupby/resample ohlc raises ValueError for pyarrow numeric dtypes #71940
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions (no new arguments/methods/functions).
• Added an entry in the latest whatsnew file if fixing a bug or adding a new feature.
• I did not use AI to develop this pull request.
• I used AI to develop this pull request. I prompted it to follow the repository contribution guidance, reviewed and understood every change, and described above how I used it and exactly which tool and model.

[github-actions]

Thanks for the pull request, @2Zest! It's linked to #71940, which is currently assigned to @JMBorrill, who's already working on it. We keep one contributor per issue to avoid duplicated effort. If @JMBorrill has had no activity for 7 days, the issue is released automatically and you'll then be able to claim it with /take on #71940 — for now, please coordinate with them on the issue. See the contributing guide for details.

I've closed this pull request for now — none of your work is lost. Once #71940 is assigned to you, ask a maintainer to reopen it.