Audit NPC body proportions against a shared guide

Measure all eight exported characters and record the stylized proportion bands. All variants pass; no skeleton or mesh rescale was needed.

docs/npc-proportion-audit.md

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+# NPC proportion audit
+
+Status: audited 2026-11-02. All eight library variants are inside the stylized
+proportion guide; no geometry correction was required in this pass. The report
+is repeatable from the exported GLBs:
+
+```bash
+python3 tools/npc_proportions.py report
+python3 tools/npc_proportions.py report --json
+```
+
+## Method
+
+`tools/npc_proportions.py` reads the GLB meshes and rest-pose joint hierarchy:
+
+- height from the full mesh bounds;
+- head height, width and aspect from `Head`/`skin` vertices (hair excluded so
+  long hairstyles do not change the head measurement);
+- shoulder silhouette from vertices in the upper-chest band around the
+  shoulder joint;
+- hip width from `HipL`/`HipR` pants vertices;
+- torso length from the Spine joint to the shoulder joint;
+- leg length from the Spine joint to the lowest vertex;
+- arm length from the shoulder joint to the Hand joint;
+- foot length from the forward extent of the KneeL/KneeR shoe vertices.
+
+All ratios are divided by total standing height except `head_aspect`
+(width / head height).
+
+## Guide
+
+These are stylized-but-credible bands for the game's low-poly adults, not
+photoreal anatomy. The broad build is allowed a larger shoulder/hip silhouette
+than the slim build.
+
+| Ratio | Target | Notes |
+| --- | ---: | --- |
+| `head_height` | 0.16–0.22 | deliberately larger than a realistic 0.13–0.15 |
+| `head_aspect` | 0.70–1.00 | width / height; rounded heads are acceptable |
+| `shoulder_width` | 0.28–0.38 | silhouette includes sleeves and build scaling |
+| `hip_width` | 0.17–0.23 | pants-only width, not skirt/coat flare |
+| `torso_length` | 0.28–0.38 | Spine joint to shoulder |
+| `leg_length` | 0.40–0.48 | Spine joint to ground |
+| `arm_length` | 0.28–0.38 | shoulder to hand |
+| `foot_length` | 0.12–0.18 | shoe forward extent |
+
+## Result
+
+| Character | Height | Head | Aspect | Shoulder | Hip | Torso | Leg | Arm | Foot | Result |
+| --- | ---: | ---: | ---: | ---: | ---: | ---: | ---: | ---: | ---: | --- |
+| `npc_casual` | 1.824 m | 0.190 | 0.907 | 0.320 | 0.209 | 0.307 | 0.449 | 0.329 | 0.144 | PASS |
+| `npc_jacket` | 1.824 m | 0.190 | 0.907 | 0.325 | 0.209 | 0.307 | 0.449 | 0.329 | 0.144 | PASS |
+| `npc_coat` | 1.824 m | 0.190 | 0.907 | 0.329 | 0.209 | 0.307 | 0.449 | 0.329 | 0.144 | PASS |
+| `npc_vest` | 1.819 m | 0.191 | 0.907 | 0.321 | 0.210 | 0.308 | 0.451 | 0.330 | 0.144 | PASS |
+| `npc_dress` | 1.825 m | 0.190 | 0.907 | 0.287 | 0.191 | 0.307 | 0.449 | 0.329 | 0.144 | PASS |
+| `npc_hoodie` | 1.856 m | 0.187 | 0.907 | 0.320 | 0.205 | 0.302 | 0.442 | 0.323 | 0.141 | PASS |
+| `npc_firefighter` | 1.819 m | 0.191 | 0.907 | 0.356 | 0.225 | 0.308 | 0.451 | 0.330 | 0.148 | PASS |
+| `npc_guard` | 1.819 m | 0.191 | 0.907 | 0.370 | 0.219 | 0.308 | 0.451 | 0.330 | 0.144 | PASS |
+
+No variant is outside a band, so the body pass does not need a global skeleton
+or mesh rescale. The values closest to a boundary are:
+
+- **head height 0.190** against the 0.22 upper bound, and **head aspect 0.907**
+  against 1.00 — the head is deliberately large. Any head-size change must be
+  coordinated with the face/headgear pass and its gear-fit measurements.
+- **guard shoulder 0.370** and **firefighter hip 0.225** against the broad-build
+  upper bounds — these are the intended uniform/turnout silhouettes, not
+  outliers.
+- **leg length 0.449** and **torso 0.307** sit inside the guide for all variants;
+  the earlier short-leg impression came from the hip joint position, not the
+  visible pelvis line.
+
+## Follow-up
+
+The proportion audit does not replace the visual criteria in
+[`npc-visual-review.md`](npc-visual-review.md): neck/shoulder/hip transitions,
+face depth, hand grips, clothing hems and shoes still need the appearance pass.
+Re-run the audit after any body mesh or skeleton change and record the new
+ratios here.