Body-physics research (hugs + Nimso Hybrid Presence + Box3D facts), mark grab v5.3.1 validated, note Box3D fork

AGENTS.md

@@ -21,7 +21,11 @@ embodiment/view system in particular is theory until proven.
   Physics"`. Validation spike (`scenes/physics_spike.tscn`, run headless) PASSES: drop+contact
   and velocity-chase-into-wall both work from C#. WARNING: exactly ONE `.gdextension` file may
   exist — a stray duplicate (e.g. at `addons/` root) double-loads the library and breaks the
-  server with "required virtual method" errors. Jolt (built-in) is the fallback: reverting is
+  server with "required virtual method" errors. **We own a fork** —
+  `https://github.com/Foxyz1302/godot-box3d` (branch `rigid-weld-joint`, carries the weld
+  patch; PR to upstream pending, owner-side) — and it may gain more additions in the future
+  (rebuild recipe + source in `.vendor/`, only the Linux binary is patched locally).
+  Jolt (built-in) is the fallback: reverting is
   the one project-setting line, and all gameplay code must stay standard-Godot-physics-node
   based so that flip is lossless.
 - Character import (Koikatsu etc.) is a separate pipeline owned by someone else. We consume a
@@ -201,6 +205,7 @@ device only; the editor has an XR simulator for dev. Trackers/action map: see `x
    Headless regressions: `scenes/weld_spike.tscn` (addon patch), `scenes/physics_spike.tscn`,
    `scenes/grab_spike.tscn` (rigid pose under drag + fast spin — the winch regression; don't
    tighten rotation limits below ~2°, that's the gravity floor for off-center grabs).
+   **Grab v5.3.1 VALIDATED in-headset (owner: "it just works") — grab saga closed.**
    `PhysicsHands.cs`: physical palm bodies (0.4 kg, 90 N chase, rotation lock, stuck-safety
    snap — SUSPENDED for a hand while it grips, HAND ghosts > 10 cm lag). Collision layers:
    1 = world, 2 = UI (panel mask 0 — props pass through even when shown); layers live on