Body Stage 1 failed first playtest (NaN solver blowup: seated chest-in-table + two-handed anvil weld); failure brief for external agent; docs marked, body track blocked pending diagnosis

AGENTS.md

@@ -228,18 +228,25 @@ device only; the editor has an XR simulator for dev. Trackers/action map: see `x
    (arm IK, IK stability/deep, grabbing, two-handed grab/Box3D internals, addon weld patch,
    body physics hugs, body physics Godot facts) — READ before re-researching or changing
    grab/IK/body. Stink-O's box3d-godot (custom components) = documented plan-B.
-8. **Body physics Stage 1 — PHYSICAL CHEST, implemented 2026-10-01.** `PhysicsTorso.cs`:
+8. **Body physics Stage 1 — PHYSICAL CHEST, implemented 2026-10-01, FAILED first playtest.**
+   `PhysicsTorso.cs`:
    one chase-driven RigidBody3D (30 kg box, gravity off, CCD) toward an HMD-derived target —
    the PhysicsHands PD pattern at body mass (2400 N budget), orientation = slewed
    angular-velocity servo (self-rights, holds yaw), 2 m snap safety, torso-yaw spring moved
    here from BodyRig. Camera stays KINEMATIC — torso chases the head, never the reverse
    (Boneworks sickness lesson). No self-collision with own hands (layer scheme above).
-   `BodyRig.cs` is VISUALS-only now (head cube + 2-bone analytic arms, soft IK, elbow pole,
+   **First in-headset session NaN'd the solver** (owner seated: chest overlapped the table;
+   two-handed 50 kg anvil weld pressed into it → `!v.is_finite()` transform flood, "head
+   detaching from the body"). **DO NOT extend the body track until diagnosed** — analysis,
+   hypotheses and the headless-repro plan live in `research/body-stage1-failure-brief.md`
+   (self-contained, forwardable to the owner's external agent). `BodyRig.cs` is
+   VISUALS-only (head cube + 2-bone analytic arms, soft IK, elbow pole,
    reach budget feeding `PhysicsTorso.ReachOffset`). Headless regression:
    `scenes/body_spike.tscn` must print "BODY: overall PASS" (also proves the Box3D pair
-   rules: one-way contact, hand-through-chest exclusion, prop contact). Stage 2 (physical
-   arm chains + hierarchical per-joint budgets, Nimso/Boneworks tier) awaits the owner's
-   Stage-1 feel verdict; design + prior art in `research/vr-body-physics-hugs.md`,
+   rules: one-way contact, hand-through-chest exclusion, prop contact) — note its repro gap:
+   no static-table overlap, no welded heavy props. Stage 2 (physical
+   arm chains + hierarchical per-joint budgets, Nimso/Boneworks tier) is BLOCKED on the
+   Stage-1 fix; design + prior art in `research/vr-body-physics-hugs.md`,
    stack facts in `research/vr-body-physics-godot.md`.
 9. **Getting a body (rig) — placeholder v1.3 (cube character, agent-built).** `BodyRig.cs`:
    all-BOX primitives (owner preference) — head 0.15³ behind the eyes, slim torso retracted,