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>

HANDOFF.md

@@ -302,10 +302,9 @@ Floor StaticBody mask 1|3|4|5 (collision_mask 29).
   does NOT hold the hand back, and forces on the arms don't reach the chest — both need a
   coupling decision (script-side feedback vs joints) the owner should weigh in on after
   feeling 2a.
-- **Seated calibration** — BodyRig calibrates proportions from the head height at first
-  frame; seated (1.01 m) clamps arm length to the 0.50 m minimum, so normal reaches saturate
-  `ReachOffset` and lean the chest into the table (stable, but wrong proportions). Needs a
-  standing calibration step or a seated mode — owner's call.
+- **Arm length was too short** (owner, playtest) — the placeholder rig derives arm length from the head height at
+  first frame (×0.46, clamped 0.50–0.72 m). Fix with the ragdoll rebuild: saved calibration profile (stand straight +
+  "arm circles" sphere fit), see `research/vr-avatar-arm-length.md`.
 - **Chest plows table props** when seated at the table (props thrown up to ~3.8 m/s by the
   2400 N chest). Honest physics; tune by feel.
 - **AnchorMoveMode NEEDS FIXING (owner playtest report, 2026-10-01)** — two-hand turning