ArWen 2.6.0

One ice category, measured against WRF's own Fortran.

New:

• P3 microphysics (mp_physics = 50): one ice category carrying a predicted
  rime mass fraction and rime density, on the card by default. p3_backend
  selects cuda, fused, or the reference CPU transcription; the two
  device arms are byte-identical on every fixture.
• The port is measured against unmodified WRF Fortran (module_mp_p3.F,
  v4.5.2, -O0) over twelve fixtures: 4 of 12 bit-identical, five more within
  2-7 ULP. The executable oracle ships in the tree. Maturity stays
  implemented-unverified; the open items are named in the registry row.
• P3 is reachable through every seam: namelist import, the stock-WRF
  initialization inventory, real-data starts with analyzed hydrometeors,
  nest births, a wrfinput handoff, and legacy RRTMG's one-category-ice case.
• P3 nest edges run in both directions against every ported partner, a
  defined and documented extension where WRF forbids mixed selectors: the
  merge conserves mass, the split conserves rime mass and volume, and P3's
  own bounds hold by construction.
• The native-HRRR route admits P3 through a registered template, and the
  admission list is derived from the ported set instead of maintained by
  hand.
• The offline downscale reads an mp=50 parent.
• Milbrandt-Yau (mp=9) starts from its analyzed hydrometeors instead of
  condensate-free.
• A cu_physics=3 import names its scheme generation (WRF v4.6.1
  Grell-Freitas, not v4.8.0's Grell-Freitas-Li); the two namelists are
  byte-indistinguishable and the substitution used to be silent.
• Mesh generation is faster on both arms, --triangulation incremental
  serves never-built hi-res construction, and sub-kilometre meshes now
  generate instead of being refused.
• CF time units that declare a real UTC offset decode to the instant they
  name, in both Rust readers.
• A mutation-testing leg joins the battery: deliberately broken Rust must be
  noticed by a test. Its first run over the estate surfaced six real
  defects, all fixed.

Fixed:

• The mesh steepest-gradient gate could step over a refinement transition
  narrower than its sample lattice and admitted a spec at 7.3x its ceiling;
  probes now cover declared variation and partial coverage refuses.
• gpuwm downscale of an mp=10 parent died at its first radiation call on
  rounding-scale negative moments.
• A supercooled liquid-only cloud radiated as clear sky under
  ra_lw_physics=1; cloud-fraction species flags now resolve per scheme.
• Rendering a Rust-written classic history tape no longer dies at the Times
  variable.
• A prepared domain tree written by an earlier version binds again after
  upgrade.
• Writers landing on tracked files stop translating newlines.
• rw_mpas_mesh --dry-run prints its JSON record alone again.