Record the Quaternius pose-sync blockers (GLB skinning + non-180° rest pose formula)

MEMORY.md

@@ -127,6 +127,11 @@ canonical implemented-features list in `docs/development-status.md`.
   out of a portrait frame (park the rest of the crowd away instead).
 - Blender: `bisect_plane` and thin bevels leave zero-area triangles (Godot "non-finite normal in
   LOD generation"); `_clean()` + a weld after bisect fixes them and the audit rejects them.
+- Quaternius arm-down bake: pose-rotate `UpperArm.L/R` −90° local X → apply Armature modifier →
+  `armature_apply` → re-add modifier bakes the rest, but `export_apply=True` writes wrong inverse
+  bind matrices (Godot renders A-pose even though the rest is arm-down). The runtime `_pose_bone`
+  `rest * Quaternion(axis, angle)` only cancels when `rest² = identity` (old rig's 180° rest); the
+  Quaternius ~76° rest does not, so the pose formula must be re-derived for a non-180° rest.
 - Image models have per-model size floors/caps (Seedream needs 1920+; `GEN_SIZE=2048`, do not
   lower; gpt-5-image-mini caps lower). `generate_image` applies model-specific sizing; concept
   generation defaults to `--request-size 1536`.