cudf-query-engine-builder

Build the first native, single-GPU cuDF path in a query engine, or complete its initial adapter. Use for libcudf C++ or cuDF Java implementation, buffer ownership, worker readiness and CPU/reference comparison, including identifying missing POC inputs. Excludes standalone dataframe analysis, cuDF mainline changes, production integration and distributed or multi-GPU execution. Bundled maintainer evaluations use CPU simulations and source review; they do not run CUDA.