Research: avatar arm length vs real arm length (Porssut 2022, Ponton CHI 2024, fitted avatars 2023, VRChat/Bonelab/Nimso) -> decision: fitted physics body + calibrated arm length, avatars as skins; fix seated-arm wording

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

research/nimso-project-tx.md

@@ -376,8 +376,9 @@ Default anthropometry when only height H is known — **Winter, Biomechanics and
   T-pose/max-reach calibration override arm length (armLen = (wingspan − 2·0.129H)/2 − grip offset); model the
   clavicle as its own driven segment (sternoclavicular → glenohumeral, 0.129H) with elevation/protraction limits
   so reach "beyond" the arm comes from shoulder lift/protraction + chest lean, exactly Nimso's "the shoulder moves
-  up as you lift your arm". Seated play: calibrate standing once and keep the profile (seated head height must not
-  shrink the body — the VR Messs playtest bug).
+  up as you lift your arm". Arm length must come from a saved calibration, never from the current head height
+  (the placeholder rig derived it from head height ×0.46, clamped to ≥ 0.50 m — the owner's "arms were just short").
+  Full decision + sources: `vr-avatar-arm-length.md`.
 
 ## 4. Still unknown (must be designed/tuned by us)
 Exact ground-control force law and gains; muscle drive gains/torque budgets per joint; the elbow "simple