Drive the real NegPy desktop app headlessly and capture rendered evidence — use when verifying pipeline/UI changes end-to-end (not via pytest).
Use when the user supplies a film-stock spec sheet, datasheet, or spectral data (PDF / URL / numbers) and wants a NegPy spectral-crosstalk .toml matrix for the Process panel's Crosstalk control, or asks to calibrate / derive channel-unmixing for a specific film or scanner. Keywords: crosstalk, datasheet, spec sheet, film stock, dye density, spectral, separation, unmixing, toml.
Use when a deliberate look/pipeline change has shifted NegPy's golden / characterization test values and they need updating — e.g. after changing the working-space TRC or primaries, the print curve, a lab/toning default (saturation, vibrance), or any default that alters rendered output, and a snapshot test now fails. Keywords: golden, goldens, characterization test, snapshot, regenerate, update expected values, test_scene_linear_relocation, test_characteristic_curve, _GOLDEN, look drift.