feat: overhead gantry top bar with a docking sign window

The top bar becomes a steel gantry. Its centre window is a mask cut-out the
3D exit sign docks into; between signs the window shows the dash read-out.
The drive controls move into the right bay, and the reading viewport is
clipped at the beam, so the empty band under the bar is gone.

src/scene/world/environment.ts

@@ -8,7 +8,6 @@ import { createHorizonAir } from '@/scene/world/horizon-air';
 import { createExpressway } from '@/scene/world/expressway';
 import { createDistricts } from '@/scene/world/districts';
 import { createSignStage } from '@/scene/world/sign-stage';
-import { usesRoadsideSign } from '@/scene/world/sign-layout';
 import { createSpeedWake } from '@/scene/world/speed-wake';
 import { createRoad } from '@/scene/world/road';
 import { createTerrain } from '@/scene/world/terrain';
@@ -175,7 +174,6 @@ export async function createProceduralSceneGeneration(
   let disposed = false;
   let renderedFrames = 0;
   let atmosphericTime = 0;
-  let signCameraWeight = 0;
   let overdrive = 0;
   let terrainSurge = 0;
   let musicPulse = 0;
@@ -186,6 +184,7 @@ export async function createProceduralSceneGeneration(
   let introProgress: number | null = null;
   let introFrames = 0;
   let introSlowFrames = 0;
+  let gantryState = '';
 
   const resize = (): void => {
     const nextWidth = Math.max(1, canvas.clientWidth || canvas.width || 1);
@@ -427,23 +426,11 @@ export async function createProceduralSceneGeneration(
       // The document stays native. Only the rendered lens eases to the chapter's safe zone.
       const cameraX = wideComposition ? composition.x : 0;
       const targetX = 0;
-      const signTarget =
-        usesRoadsideSign(width, height) && snapshot.sign !== null
-          ? snapshot.sign.phase === 'depart'
-            ? 1 - snapshot.sign.progress
-            : 1
-          : 0;
-      signCameraWeight +=
-        (signTarget - signCameraWeight) * (1 - Math.exp(-deltaSeconds / 0.48));
       const targetShift =
         height < 560 && width >= 768
           ? 0.22
           : wideComposition
-            ? THREE.MathUtils.lerp(
-                composition.shift,
-                composition.shift * 0.28,
-                signCameraWeight,
-              )
+            ? composition.shift
             : 0;
       const targetVerticalShift = wideComposition
         ? 0
@@ -558,14 +545,12 @@ export async function createProceduralSceneGeneration(
         camera.updateProjectionMatrix();
       }
       const stage = signStage.update(width, height);
-      sign.compose(
-        camera,
-        width,
-        height,
-        stage.navigationBottom,
-        now,
-        car.group.position,
-      );
+      sign.compose(camera, width, height, stage.dock, now, stage.tilt);
+      const gantry = sign.dockState();
+      if (gantry !== gantryState) {
+        gantryState = gantry;
+        document.documentElement.dataset.gantry = gantry;
+      }
       if (TEST_BUILD && snapshot.sign !== null) {
         const presentation = sign.inspect(camera, width, height);
         if (presentation !== null) {
@@ -600,6 +585,7 @@ export async function createProceduralSceneGeneration(
     dispose() {
       if (disposed) return;
       disposed = true;
+      delete document.documentElement.dataset.gantry;
       // Quality changes reuse the canvas context. Leave texture upload flags at
       // defaults before the next renderer creates its empty array textures.
       const gl = renderer.getContext();