fix(pipeline): check that a character is CORRECT, not merely well-formed

Seven characters shipped "All checks passed" and four were visibly broken
in game — lying on their backs at seven times scale, facing backwards, or
holding a gun that floated near their chest. Nothing in the suite was
wrong; it just never asked the questions that mattered. That distinction
is the whole lesson, and it is now written down in the skill as
references/failure-modes.md, generalised per failure.

Two root causes are measured and certain:

- flatten_and_scale() normalises the bounding box along Blender Z because
  Z is up. For a model that arrives lying along Y that measures the
  character's THICKNESS, so it scales by ~7 and leaves them on their back.
  One assumption, both symptoms. The trap is that the normalised number
  always comes out right — the exporter maps Blender Z to glTF Y, so "is
  the height 1.75" passes on a character who is 7.5 m tall lying down.
  All three casualties are VRM files that went through a Blender
  round-trip and came back with a baked axis rotation.

- SkinnedPlayerModel.set_weapon() finds the hand with three hardcoded
  spellings, which match none of the four non-Rigify rigs — their hands
  resolve perfectly in the sidecar as "Right wrist" and "J_Bip_R_Hand".
  When it misses, the weapon is parented to the model root at a fixed
  chest offset, so it is not attached to the character at all. Same class
  of bug as the leg check that name-matched thigh/shin. rig_map.py exists
  so nothing downstream has to guess a bone name; only some consumers read
  the roles it publishes.

Three new hard checks, none needing more than the vertices and the
sidecar:

  character stands up in world space   — against WORLD up, not against the
      model's own proportions. "Is the spine the longest axis?" catches
      nothing: a model rotated as a whole is internally consistent and
      passes it comfortably.
  character is a plausible size / height
  every role the runtime needs is resolved

They separate the four good characters from the three broken ones on the
first run. Also fixed the posture measurement to read vertices rather than
object.bound_box, which is cached and still stale right after an import —
it reported a 1.75 m character as 1.18 m tall.

Recorded but not yet fixed: kiyoko faces backwards (facing is inferred by
two independent mechanisms and verified by neither), miku's grown hair
chains stretch under animation (generated chains are never validated
against the geometry they drive), and the mannequin's rifle hold does not
convince despite resolving correctly.

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

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

@@ -66,6 +66,18 @@ It also applies the collider's `from` offset, so it tests the same band of thigh
 the solver is defending. Measuring the full bone tests the hip cap the solver
 deliberately excludes and reports it as clipping no tuning can fix.
 
+## What the suite still does not check
+
+It verifies that a character is WELL-FORMED, not that it is CORRECT. Those are
+different properties, and only the first was ever asserted — which is how four
+characters shipped "All checks passed" while lying on their backs, seven times
+too large, facing backwards, or unable to hold a gun. See `failure-modes.md`.
+
+`posture` and `bone roles reachable at runtime` are now hard checks. Still
+missing, and worth adding when a source next exposes them: facing measured on the
+OUTPUT, and per-vertex validation that a generated cloth chain actually tracks
+the geometry it was given.
+
 ## Diagnosing "the solver isn't working"
 
 In order: