fix(pipeline): stand the character up before scaling; reach bones by role

Fixes the two root causes behind four of the seven reported breakages, and
rejects the source that cannot be fixed.

STAND UP FIRST. flatten_and_scale() now derives the up axis from the
skeleton and rotates the model upright before measuring anything. Aria and
Momo are correct: 1.75 m tall, 1.43 x 0.41 and 1.52 x 0.39 across, verified
by render.

The up vector is measured from the FEET to the HIPS, not from the hips to
the head. The head is not a reliable landmark — the spine walk ends on the
last non-cosmetic bone in the chain, which on a rig with a facial skeleton
can sit BELOW the hips. Momo's did, so the first cut of this fix stood her
neatly on her head: right size, right proportions, upside down. Feet cannot
be mistaken.

REACH BONES BY ROLE. SkinnedPlayerModel gained _role_bone(), and set_weapon
uses it. Four characters could not hold a gun because one hardcoded lookup
knew three spellings and their hands are called "Right wrist" and
"J_Bip_R_Hand" — both resolved perfectly in the sidecar the whole time.

HIKARI IS REJECTED. She now fails the gate: her feet and spine disagree
about which way is up, so the stand-up correction cannot resolve her
either, on top of zero-length cosmetic bones and a second armature that was
smuggling its own clips into the export. That is not a tuning problem, it
is a file that has been through two toolchains. De-registered and removed
rather than shipped broken — which is what the gate is for.

Six GLB skins remain, all passing. Smoke 0 failures, 11/11 movement tests.

Still open, recorded in the skill: kiyoko faces backwards, miku's grown
hair stretches under animation, the mannequin's rifle hold does not
convince, and taila's front skirt clipping.

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

.claude/skills/character-pipeline/references/failure-modes.md

@@ -52,8 +52,16 @@ That is exactly what makes the bug invisible: **the number you normalised always
 comes out right, whether or not it was the right number.** A check on "is the
 height 1.75" passes on all seven of these.
 
-**Rule:** derive the up axis from the SKELETON (hips → head), not from a
-convention, and rotate the model upright before scaling anything.
+**Rule:** derive the up axis from the SKELETON, and rotate the model upright
+before scaling anything. `flatten_and_scale()` now does this.
+
+**Measure it from the FEET to the HIPS, not from the hips to the head.** The head
+is not a reliable landmark: the spine walk ends on whatever the last non-cosmetic
+bone in the chain is, and on a rig with a facial skeleton that can be a bone
+sitting BELOW the hips. Momo's did, so the first version of this fix stood her
+neatly on her head — correct size, correct proportions, upside down. Feet cannot
+be mistaken; they are the bottom of a standing character on every rig, and
+`foot.L/R` have resolved on every source met so far.
 
 **And compare it to WORLD up, not to the model's own proportions.** The obvious
 test — "is the spine the longest axis of the bounding box?" — catches nothing
@@ -172,7 +180,25 @@ than judging by eye.
 
 ---
 
-## 6. Known-unsolved, and honestly so
+## 6. Some sources are not salvageable, and the gate should say so
+
+**Hit:** hikari. She failed every way at once — stretched and warped, tiny, far
+away, gun backwards. Her rig has been through at least two toolchains: her
+cosmetic bones are zero-length terminators, she carried a second armature with
+its own clips, and her feet and her spine disagree about which way is up, so the
+stand-up correction cannot resolve her either. She is now REJECTED by the gate
+and removed from the roster rather than shipped broken.
+
+**Rule:** a source that fails several unrelated checks is not a tuning problem,
+it is a bad file. Spend the effort on finding a cleaner source, not on repairing
+this one — and make sure the gate blocks it, because the failure mode before this
+work was that everything passed and the breakage was only visible in game.
+
+The vetting snippet in `separation.md` catches most of these before download:
+several meshes, 50+ joints, cosmetic bones present. Add a look for duplicate
+armatures and for bone chains whose bones are all at the same position.
+
+## 7. Known-unsolved, and honestly so
 
 Taila's legs still clip through the front of her skirt in a run, slide and dash
 (~95 mm). See `cloth-and-hair.md`. The solver sees the contact and pushes on it