A 0.5 °F drift gate, and the advisor that caught the formula bug before it shipped

Building heat-metrics-lab required getting two things right in Phase 1: a JS-vs-Python parity gate holding both implementations within 0.5 °F of known reference cases, and formula correctness against Liljegren 2008 and Rothfusz 1990. The drift gate solved parity. The advisor — a pre-implementation reviewer running a stronger model against the same conversation context — caught a 6.68 °F RMSE error in the WBGT globe-temperature formula before any implementer touched the code.