Epic 5 Phase 2.5 — model blend via alpha, not lumakey

Model stages render with alpha:0 where no mesh covers (transparent
clear) and carry dark material colours. Lumakey keys on luma
(dot(src,0.212…)), so a dim mesh keyed to ~0 and vanished — Pylon
Field 3D / Synthwave Corridor looked black. Use 'normal' for
kind:'model' so the alpha is the mask; fragment over dark ground
stays covered. Per-stage fog/light tuning deferred to a director
param (LookGenerator) per review — not hand-tuned per stage.

Co-Authored-By: Claude <noreply@anthropic.com>

flow-state/src/look/LookGenerator.js

@@ -625,7 +625,13 @@ function buildStack(module, overlayRoster, bias, rng, temperament, story = null,
         // leaves unpainted is then the ground rather than black, which is the
         // whole point of standing it on one, and what it DOES paint stays its
         // own colour. 'screen' is the blaze — see above, and passes.js.
-        blend: standsAlone ? 'normal' : (blaze ? 'screen' : 'lumakey'),
+        // Model stages render with correct alpha (transparent clear) and carry
+        // dark material colours — lumakey would key them out. Use normal for
+        // kind:'model' so the alpha is the mask (Assembly, Pylon Field 3D,
+        // Synthwave Corridor).
+        blend: module.kind === 'model'
+            ? 'normal'
+            : standsAlone ? 'normal' : (blaze ? 'screen' : 'lumakey'),
         // Carried so the HUD, the checks and a later pass over the look can all
         // tell a deliberate bloom-out from a broken one.
         blaze,