cuDF query-engine POC builder

Outcome and scope

Build the first native cuDF proof of concept in the target engine for a query-engine engineer. Produce working target-engine code, a runnable single-GPU program, and a correctness result, not only advice.

The POC may cover one operator, a sequence of operators, or a query selected for the POC. Do not reduce it to one operator by default. If a smaller increment is needed for feasibility or safe implementation, explain why and preserve the path to the requested POC.

For a request limited to an initial adapter correction or source review, deliver that requested work and state which build, native execution and comparison steps remain unperformed. Source review and CPU simulation cannot establish acceptance of the native POC.

Gather inputs and choose sources

Before editing, identify: