ArWen 1.9.1

Fast follow for 1.9.0. Three defects caught by head-to-head verification against stock WRF v4.6.1, each closed with a class instrument so the pattern cannot ship again.

Fixed:

• Milbrandt-Yau (mp_physics = 9) runs real cases. Seven scheme-keyed tables lacked mp=9 arms; the coupling sets now read one shared inventory, and a new stage-1 suite proves every accepted mp_physics value builds its workspace, classifies, couples, and digests.
• WDM6 and Milbrandt-Yau own the SR roundoff envelope WSM6 already had, keyed on the audited shared-expression family with an analytic bound per member. Healthy runs no longer die one ULP above 1.0.
• RRTM longwave with Dudhia shortwave (1/1) finishes cleanly. p_top is coerced like the legacy adapter, and every registered radiation callable now classifies through the restart manifest.

Known:

• The time-zero history frame publishes the declared constant downward longwave, 300 W m-2, where WRF writes 0.0. The first radiation call overwrites it.

Verification: the fixed schemes were re-run on the reference case and judged against stock WRF v4.6.1; deltas sit inside same-scheme calibration bands.