tools: measure rest poses, and diagnose momo

momo's idle plays with her arms overhead and her waist pinched, and every
assertion in the suite passes on her.

The first suspicion was the retarget's rest-relative delta: it applies "what the
clip does to the LIBRARY's rest" to THIS rig's rest, which quietly assumes the
two rests are alike. rest_pose_check.gd tests that, and disproves it — miku's
arms rest 41° off the library's and taila's 32°, and both animate correctly. The
delta retarget handles a rest-pose difference, which is what it is for. Recorded
in the reference so nobody spends that hour again.

Writing the tool reproduced this project's own recurring mistake in miniature.
Measuring "the direction from a bone to its first child" reported kiyoko's and
aria's legs 71° off the library — because a thigh's first child is as likely to
be a skirt bone as a shin, and it was measuring the hang of a skirt panel.
Pointing it at the next limb BY ROLE dropped both to 1°.

What momo actually has: `Root_001` through `Root_007` are in her driven_bones,
and they are her HAIR roots — Hair_A is dominated by Root_001_001, Root_007 and
Root_005. The animation is keying bones the spring solver is supposed to own,
which is non-negotiable #2 broken by the role resolver rather than by a clip.
The surface table corroborates it: her hair surfaces report 1.8% and 9.4% chain
share, because most of their vertices belong to bones in no chain at all.

Not fixed here. `Root_00N` matches no COSMETIC stem, and adding "root" to the
stems would cost a rig whose actual root is called `Root` its hips. The
structural fix is that a bone whose geometry is dominated by a mesh classified
`hair` is a hair bone whatever it is called — which the surface table makes
answerable at build time, and did not when momo was imported. It needs a Blender
re-run and re-verification of all six characters.

Co-Authored-By: Claude Opus 5 <[email protected]>

.claude/skills/character-pipeline/references/verification.md

@@ -47,6 +47,22 @@ Two related traps:
 | `anim_capture.gd` / `orbit_capture.gd` | renders, for looking | — |
 | `roster_capture.gd` | one photo of every character, from the picker | — |
 | `ui_capture.gd` | one photo of every menu screen | — |
+| `rest_pose_check.gd` | each rig's bind-pose limb directions vs. the library's | see below |
+
+## What `rest_pose_check` actually established
+
+It was written to test a suspicion — that the rest-relative retarget silently
+assumes both rigs rest alike — and it disproved it. Miku's arms rest **41°** off
+the animation library's and Taila's **32°**, and both animate correctly. The
+delta retarget handles a rest-pose difference, which is what it is for. Do not
+go looking there again.
+
+It also demonstrates the measurement trap in miniature. Written as "the direction
+from a bone to its FIRST CHILD", it reported kiyoko's and aria's legs 71° off —
+because a thigh's first child is as likely to be a skirt bone as a shin, and it
+was measuring the hang of a skirt panel. Pointing it at the next limb BY ROLE
+dropped both to 1°. The same rule as everywhere else in this pipeline: resolve
+roles, never take whatever the rig happens to hand you.
 
 ## Assert the consequence, not the plumbing