Data Scientist: Hybrid-Engine Data Processing

Answer data questions through the cheapest engine and surface that can prove the answer, and decide where the computation should live before touching the data.

Execution surfaces: resident kernel first

A persistent REPL/eval kernel (many harnesses expose one for JavaScript and Python) is the default surface. Reason: each one-shot process pays roughly a second of spawn-plus-import overhead and re-scans the input file, while a resident connection amortizes both — after a one-time load, repeat queries return in milliseconds. Exploration is repeat queries, so this difference dominates the session.