[WilliamK112]

Cleaning a three-row pandas frame with no columns through the native Polars path returns (0, 0) on Polars 1.36 without a fallback record. Route nonempty, zero-column pandas inputs through the existing recorded pandas fallback before ingestion, preserving their rows, index, and report counts with pandas output.

The existing allow/warn/error fallback policy applies. Native-handle requests receive the disclosed pandas result, as with other input-driven fallbacks; a zero-row input with a RangeIndex still stays native. Also skip duplicate handling once the native schema has no columns, matching pandas and preventing Polars 2.0 from reporting or collapsing those rows as duplicates. Update the fallback matrix and changelog.

Fixes #463.

Validation on Windows / Python 3.12:

• Reproduced the row loss on Polars 1.36.1; five new regressions failed before the fix. All 92 focused Polars, DuckDB, ingestion/output, and fallback-policy tests pass after it.
• After the matrix compatibility follow-up, all 52 Polars/engine-parity cases pass on both pandas 1.5.3 + Polars 1.36.1 and pandas 2.3.3 + Polars 2.0.0, including dedup enabled/disabled after dropping every column. The new empty-input test explicitly supplies a RangeIndex because pandas 1.5 otherwise constructs an unsupported generic index.
• Full fast lane on Polars 2.0.0: 7,610 passed, 49 skipped, 5 failed, and 94.99% coverage. All five failures reproduce on clean main@ba3f01f in this environment (Windows quoting/newline/filename fixtures and the zero-time semantic budget test).
• Full Ruff check passes. Mypy passes for all 205 source files with --platform linux and numpy<2.5, matching CI's typecheck dependency cap.

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[chatgpt-codex-connector]

Codex Review Summary

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-13T07:42:38.499751Z	722183f	PR opened

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[JohnnyWilson16]

LGTM! Cleanly fixes #463. Fallback policies are strictly enforced, input row counts and indices are preserved, and empty-column duplicate dropping in Polars is properly guarded. Ready to merge.