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

TODO.md

@@ -82,12 +82,14 @@ baseline sheet.
       ADR) indicated; do not rebuild on the warped base.**
 - [-] Skin the Quaternius mesh and verify Idle, Walk, seated and arm-down poses. The old
       MPFB/arm-retarget warps are not a reference; judge the Quaternius result directly.
-      (Direction set: ADR-0018 option 2 — 62-joint runtime. `NpcAvatar` now maps the Quaternius
-      names with old-rig fallback and derives proxy pivots from `get_bone_global_rest`
-      (commit `0cd12af`). First end-to-end capture loads and runs, but the vision judge reads
-      the arms/legs as misaligned — the `_sync_skeleton` swing axis (`Vector3.RIGHT`) is
-      calibrated for the old rig, not the Quaternius bone roll. Next: determine the per-bone
-      swing axis for UpperArm/LowerArm/UpperLeg/LowerLeg from the Quaternius rest basis.)
+      (Direction set: ADR-0018 option 2 — 62-joint runtime. `NpcAvatar` maps the Quaternius
+      names + derives proxy pivots from `get_bone_global_rest` (commits `271f10a`/`0cd12af`).
+      Two blockers remain: (1) the arm-down GLB's **skinning** renders A-pose in Godot even
+      though its rest is arm-down — the `armature_apply` + `export_apply=True` bake writes
+      wrong inverse bind matrices, so fix the Blender export first; (2) `_pose_bone` uses
+      `rest * Quaternion(axis, angle)`, which only cancels when `rest² = identity` (the old rig's
+      180° rest); the Quaternius ~76° rest does not, so the pose formula must be derived from the
+      actual `set_bone_pose_rotation` semantics for a non-180° rest.)
 - [ ] Retarget Idle and Walk from the 24 Quaternius clips to the contract rig; discard
       combat, gun and sword clips. Verify looping, foot contact and frame rate in Godot.
       (Direction set: no retarget needed — the clips are authored for the 62-joint rig; only