feat: charge terrain with acceleration and compact desktop sign staging

src/scene/world/environment.ts

@@ -164,6 +164,8 @@ export async function createProceduralSceneGeneration(
   let atmosphericTime = 0;
   let signCameraWeight = 0;
   let overdrive = 0;
+  let terrainSurge = 0;
+  let terrainSpectrumPhase = 0;
   let firstFrameSuppressionRecorded = false;
 
   const resize = (): void => {
@@ -257,6 +259,19 @@ export async function createProceduralSceneGeneration(
         (chargeTarget - overdrive) *
         (1 -
           Math.exp(-deltaSeconds / (chargeTarget > overdrive ? 0.28 : 1.05)));
+      // Terrain feedback reads acceleration directly, with its own fast attack
+      // and long release. Audio and the shared drive responses stay untouched.
+      const surgeTarget = Math.sqrt(
+        THREE.MathUtils.clamp(snapshot.acceleration, 0, 1),
+      );
+      terrainSurge +=
+        (surgeTarget - terrainSurge) *
+        (1 -
+          Math.exp(-deltaSeconds / (surgeTarget > terrainSurge ? 0.11 : 1.15)));
+      // Integrate color travel instead of multiplying elapsed time by speed:
+      // lifting off slows the spectrum to rest without rewinding its phase.
+      terrainSpectrumPhase =
+        (terrainSpectrumPhase + deltaSeconds * overdrive * 0.38) % 1;
       writeChapterPalette(targetPalette, snapshot.chapter, snapshot.chapter, 0);
       dampPalette(currentPalette, targetPalette, deltaSeconds);
       const driveDistance = travelDistance.advance(
@@ -289,6 +304,8 @@ export async function createProceduralSceneGeneration(
         snapshot.routeProgress,
         currentPalette,
         overdrive,
+        terrainSurge,
+        terrainSpectrumPhase,
       );
       atmosphericTime += deltaSeconds;
       const elapsedSeconds = atmosphericTime;