feat(character): ComfyUI blueprints and a render-vs-blueprint evaluation

Two tools that turn character work into something measurable.

- Tools/comfyui_character_blueprint.py generates a four-view sheet (front, side, back,
  head) plus a contact sheet from one description, with fixed seeds and a JSON record
  of prompts and prompt ids. First sheet: 'GigLine walker', lean pedestrian in a navy
  tee, jeans and sneakers.
- Tools/character_match.py compares a rendered character against a sheet: figure
  aspect, fill and coverage deltas, mean CIE76 colour distance, dominant-palette
  distance, and a side-by-side montage. The deltas stay separate on purpose - a single
  similarity score between a photoreal sheet and a low-detail body would be a number
  with no meaning.
- comfyui_generate.py grew wait_for_image() so both tools share the polling path
  instead of duplicating it.
- 13 unit tests for the colour maths, masks and palette; 95 tool tests pass.

First real result, recorded rather than smoothed over: aspect delta 1.24, fill delta
0.12, mean deltaE 31.9, palette deltaE 25.4. The montage shows the reason - the model
is a nude body and the blueprint wears a tee and jeans, so clothing dominates every
metric. Figure segmentation is explicit (--render-box): auto-detection picked backdrop
blobs on every attempt, and a background plate is the proper fix.

MEMORY.md

@@ -498,3 +498,10 @@ Scope: facts and traps that cost time to establish. Planned work lives in [TODO.
 - **Hair joined into the body mesh loses its material.** Blender shows two slots (hair faces on index 1) and the FBX exports both, but Unreal's skeletal-mesh import arrives with **one** slot named after the body material, so the hair renders as skin. `unreal.SkeletalMesh` has no `set_material`, so it cannot be re-slotted afterwards. A separate skeletal mesh imported on its own keeps its slot and imports cleanly (`CharacterHair` → `M_Character_Hair`).
 - **A second skeletal component follows the body with `SetLeaderPoseComponent(GetMesh())`** — no second rig, no second animation, and it hides with the body in first person.
 - **`unreal.MaterialEditingLibrary` segfaults in `-run=pythonscript`** when it clears and rebuilds a material graph. The tool ran its texture imports, then crashed the commandlet with no Python traceback. Graph editing needs an editor session, or a material created from scratch rather than edited in place.
+
+## 2026-11-09 — Character blueprints and how to compare a render to one
+
+- **A SDXL character sheet is reliable**: "full body front view, neutral pose, plain grey background, character sheet" gives a usable turnaround with fixed seeds. Four views (front/side/back/head) from one description is enough to evaluate against; the sheet and its JSON live in `Art/characters/blueprints/`.
+- **Segmenting the character out of a review shot does not work by colour.** The sky band, the pale wall and the dark pavement are each larger and more saturated than the body, so every size-based rule picked a backdrop blob and the first report measured the whole frame. `Tools/character_match.py` now takes an explicit `--render-box`; the proper fix is a background plate rendered without the character.
+- **The report has to separate the failures it measures.** Aspect, fill, coverage and two colour distances are reported apart on purpose: an absolute similarity number between a photoreal sheet and a low-detail body would mean nothing. The first real comparison (aspect Δ1.24, mean ΔE 31.9) was dominated by the model being **unclothed** while the blueprint wears a tee and jeans.
+- **`SetMaterial(0, ...)` in the pawn constructor does not visibly land** on the body mesh: `M_Character_Skin` is built and assigned, yet the render stays neutral grey. Either the slot does not exist yet at that point or the assignment is dropped; `BeginPlay` is the next thing to try.