ExtensionStoragePushdown returns storage values instead of extension values #11243

What happened?

ExtensionStoragePushdown<A, E> returns the results and partials of A over the storage unchanged, so input values lose their extension type. For example, vortex.min_max[vortex.timestamp] returns raw i64 values without the time unit or time zone, while plain vortex.min_max wraps its extrema and returns timestamps (X12). vortex.is_sorted[...] returns a correct Bool, but the first_value and last_value fields of its partial hold storage values.

Note that nothing in the repository reaches these aggregates on its own, since neither is a zone statistic default. Only an explicit binding or a serialized expression or statistic that names the composite ID does.

Steps to reproduce

pushes_down_into_storage asserts that vortex.min_max[vortex.timestamp] over a timestamp column equals plain min_max over its i64 storage.

Environment

develop at 068d8194c8. #10566 added the adapter, and #10616 registers it for Date, Time, Timestamp, and Uuid.

Plan

#11188 patched the adapter with a StorageResultMapping trait that names the fields holding input values by index ([0, 1] for min_max, [2, 3] for is_sorted). That's a half-measure, since the indices can drift from the real fields, the trait adds a contract on finalize, and #11115 removes the adapter anyway. So #11188 is closed, and the claims work fixes this instead:

• SP1 adds ExtensionUse::Storage and result mappings (X19).
• SP4 makes aggregate binding take a default storage path under the plain aggregate ID, so partials get their logical form when they leave the accumulator and the composite IDs go away (X21).

Open question for SP1: ResultMapping::Fields is still a positional list next to the dtype. Since each aggregate builds its dtypes from an element dtype (e.g., make_minmax_dtype), can building them over the extension dtype replace the mapping?

Until then, use plain min_max for the extrema of an extension column.

Additional context

• Tracking: Tracking Issue: Fix Extension Types #11114 (U9) and Tracking Issue: Extension Type Derives #11115 (SP1, SP4)
• EXT-A3 in the research notes
• Move aggregates out of vortex-array into vortex-aggregates #10769 moves the aggregates into vortex-aggregates and changes the same code