feat: weave speed-reactive terrain and ground roadside signs

Anchor desktop signs beside the road and feather the compact reading edge with measured chapter landings. Add a continuous cyan-to-coral terrain grid and a bounded rear wake that builds with existing drive speed.

Preserve approved content, media, soundtrack, and canonical journey contracts.

src/scene/world/environment.ts

@@ -6,6 +6,8 @@ import { renderQualityFor } from '@/scene/render-quality';
 import { createHorizonAir } from '@/scene/world/horizon-air';
 import { createExpressway } from '@/scene/world/expressway';
 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';
 import { createSun } from '@/scene/world/sun';
@@ -111,6 +113,7 @@ export async function createProceduralSceneGeneration(
 
   const road = createRoad(context.resources, quality);
   const terrain = createTerrain(context.resources, quality);
+  const speedWake = createSpeedWake(context.resources);
   const expressway = createExpressway(context.resources, quality);
   const signStage = createSignStage(context.resources);
   const sun = createSun(context.resources);
@@ -132,6 +135,7 @@ export async function createProceduralSceneGeneration(
     sun.group,
     horizonAir.group,
     car.group,
+    speedWake.group,
     sign.group,
   );
 
@@ -158,6 +162,8 @@ export async function createProceduralSceneGeneration(
   let disposed = false;
   let renderedFrames = 0;
   let atmosphericTime = 0;
+  let signCameraWeight = 0;
+  let overdrive = 0;
   let firstFrameSuppressionRecorded = false;
 
   const resize = (): void => {
@@ -240,6 +246,17 @@ export async function createProceduralSceneGeneration(
       lastNow = now;
       dynamics.update(snapshot.acceleration, snapshot.direction, deltaSeconds);
       const response = dynamics.snapshot();
+      // Read the existing speed contract; visual charge has its own slow release
+      // and cannot change the soundtrack or the canonical drive dynamics.
+      const chargeTarget = THREE.MathUtils.smoothstep(
+        snapshot.driveSpeed,
+        0.68,
+        0.9,
+      );
+      overdrive +=
+        (chargeTarget - overdrive) *
+        (1 -
+          Math.exp(-deltaSeconds / (chargeTarget > overdrive ? 0.28 : 1.05)));
       writeChapterPalette(targetPalette, snapshot.chapter, snapshot.chapter, 0);
       dampPalette(currentPalette, targetPalette, deltaSeconds);
       const driveDistance = travelDistance.advance(
@@ -271,6 +288,7 @@ export async function createProceduralSceneGeneration(
         snapshot.chapter,
         snapshot.routeProgress,
         currentPalette,
+        overdrive,
       );
       atmosphericTime += deltaSeconds;
       const elapsedSeconds = atmosphericTime;
@@ -287,6 +305,12 @@ export async function createProceduralSceneGeneration(
         elapsedSeconds,
         driveDistance,
       );
+      speedWake.update(
+        overdrive,
+        elapsedSeconds,
+        car.group.position,
+        width < 1100 || height < 620 ? 2.32 : 2.78,
+      );
       sign.update(snapshot.sign, now);
       atmosphere.update(
         driveDistance,
@@ -302,7 +326,7 @@ export async function createProceduralSceneGeneration(
       ambient.groundColor.copy(currentPalette.fog);
       ambient.intensity = 1.05 + currentPalette.warmth * 0.18;
       carKeyLight.color.setHex(0xb9e3ef);
-      carKeyLight.intensity = 32 + response.bloomEnergy * 3.6;
+      carKeyLight.intensity = 32 + response.bloomEnergy * 3.6 + overdrive * 8;
       carFillLight.color.setHex(0x809ec1);
       carFillLight.intensity = 12.5 + currentPalette.warmth * 2.8;
       rearLight.intensity = 4.2 + response.suspensionEnergy * 1.4;
@@ -346,11 +370,23 @@ 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
-            ? composition.shift
+            ? THREE.MathUtils.lerp(
+                composition.shift,
+                composition.shift * 0.28,
+                signCameraWeight,
+              )
             : 0;
       const targetVerticalShift = wideComposition
         ? 0
@@ -434,7 +470,14 @@ export async function createProceduralSceneGeneration(
         camera.updateProjectionMatrix();
       }
       const stage = signStage.update(width, height);
-      sign.compose(camera, width, height, stage.navigationBottom, now);
+      sign.compose(
+        camera,
+        width,
+        height,
+        stage.navigationBottom,
+        now,
+        car.group.position,
+      );
       if (TEST_BUILD && snapshot.sign !== null) {
         const presentation = sign.inspect(camera, width, height);
         if (presentation !== null) {