Author the 62-to-13 joint map and align the AGENTS.md contract with the Quaternius base

docs/npc-model-sourcing.md

@@ -136,6 +136,40 @@ canonical base built from `Casual_Hoodie.glb` (the most detailed body) by
 This is the §2 contract-bake input: the 62-joint rig is authoring-only and is mapped to the
 13-core contract next, not shipped as-is.
 
+## 62-joint → 13-core joint map (2026-11-05)
+
+The Quaternius hierarchy (measured from `quaternius_base.glb`):
+
+- `Root → Body → Hips → Abdomen → Torso → Chest → Neck → Head` (spine);
+- `Chest → Shoulder.L/R → UpperArm.L/R → LowerArm.L/R → Wrist.L/R → fingers` (arms);
+- `Body → UpperLeg.L/R → LowerLeg.L/R` and `Root → Foot.L/R` (legs — the foot is a separate
+  child of Root, not of LowerLeg);
+- `Root → PT.L/R` (IK pole targets, no deforming weights).
+
+The contract is 14 bones (13 core + `Hips` root): `Hips, Spine, Neck, Head, Shoulder.L/R,
+Elbow.L/R, Hand.L/R, Hip.L/R, Knee.L/R`. The map:
+
+| Contract bone | Quaternius source | Notes |
+| --- | --- | --- |
+| `Hips` | `Hips` | `Root` + `Body` collapse into `Hips` |
+| `Spine` | `Abdomen`, `Torso`, `Chest` | three collapse into one |
+| `Neck` | `Neck` | |
+| `Head` | `Head` | |
+| `Shoulder.L/R` | `UpperArm.L/R` | the collar `Shoulder.L/R` collapses into `Spine` |
+| `Elbow.L/R` | `LowerArm.L/R` | |
+| `Hand.L/R` | `Wrist.L/R` | |
+| `Hip.L/R` | `UpperLeg.L/R` | |
+| `Knee.L/R` | `LowerLeg.L/R` | |
+
+Optional extras (allowed by the contract; kept if they survive within 24,000 vertices):
+
+- the 30 finger bones (`Thumb×3, Index×4, Middle×4, Ring×4, Pinky×4` × L/R) → optional finger
+  bones;
+- `Foot.L/R` → optional toe bones.
+
+Dropped (never shipped): `PT.L/R` (pole targets carry no deforming weights), and the
+`Root`/`Body`/collar-`Shoulder` collapse bones above.
+
 ## Contract mismatch
 
 The expensive part is the rig and proportions, not the mesh. The source has a