Revert "feat(sky): the night sky wheels with the Dereth clock; uniform time fade with a scoped twilight band"

This reverts commit 0dac024cdb.

src/AcDream.App/Rendering/Shaders/sky.frag

@@ -43,10 +43,6 @@ layout(std140, ACDREAM_UBO_SET binding = 4) uniform SkyParams {
     vec2  uUvScroll;
     float uApplyFog;
     float uSurfOpacity;
-    float uNightSkyRotationTurns; // enhanced night sky (IA-26): sky rotation
-    float uNsPadA;
-    float uNsPadB;
-    float uNsPadC;
 };
 
 struct Light {
@@ -190,50 +186,18 @@ vec3 nightSky(vec3 dir, uint seed)
 
 void main() {
     if (uParamA > 0.5) {
-        // Day/night fade from the UNIFORM ambient term only — the first
-        // gate's vTint signal carried the per-vertex sun-facing product and
-        // blanked stars across the whole twilight half of the sky
-        // (2026-08-23 screenshots). Ambient is one value for the sky, so
-        // star visibility is even everywhere; the twilight glow gets its
-        // own tightly-scoped suppression below.
-        float dayL = dot(uAmbientColor, vec3(0.299, 0.587, 0.114));
-        float night = 1.0 - smoothstep(0.10, 0.32, dayL);
+        // The star layer's own retail lighting product (Emissive 0 ->
+        // ambient + diffuse) is the day/night signal: ~0.1 at deep night,
+        // ~1.0 at noon. Stars at full strength only under a dark sky.
+        float dayL = dot(vTint, vec3(0.299, 0.587, 0.114));
+        float night = 1.0 - smoothstep(0.18, 0.45, dayL);
         if (night < 0.004) {
             // Daytime: the whole lattice would multiply to zero — skip it
             // so the enhanced sky costs nothing outside dusk-to-dawn.
             fragColor = vec4(0.0, 0.0, 0.0, 1.0);
             return;
         }
-
-        vec3 d = normalize(vDir);
-
-        // Subtle twilight suppression: only the low sky (bottom ~19 deg)
-        // toward the sun's azimuth, and only while the sun term is strong
-        // (dusk/dawn) — stars near the bright horizon wash out, the rest
-        // of the sky keeps its full carpet.
-        vec3 dflat = normalize(vec3(d.xy, 0.0) + vec3(1e-5, 0.0, 0.0));
-        vec3 sflat = normalize(vec3(uSunDir.xy, 0.0) + vec3(1e-5, 0.0, 0.0));
-        float glowSide = max(dot(dflat, sflat), 0.0);
-        float lowSky = 1.0 - clamp(d.z * 3.0, 0.0, 1.0);
-        float twilight = clamp(
-            dot(uSunColor, vec3(0.299, 0.587, 0.114)) * uDiffuseFactor,
-            0.0, 1.0);
-        night *= 1.0 - 0.85 * twilight * glowSide * glowSide * lowSky;
-
-        // The sky wheels: one revolution per Dereth day about a celestial
-        // pole ~41 deg above the northern horizon (+Y north, +Z up), plus
-        // ~1 deg/night of seasonal drift folded into the turns value
-        // (dayFraction + dayOfYear/360). Rodrigues rotation of the sample
-        // direction; stars and mottle turn together.
-        const vec3 NS_POLE = vec3(0.0, 0.6598, 0.7514);
-        float ang = 6.28318530718 * fract(uNightSkyRotationTurns);
-        float ca = cos(ang);
-        float sa = sin(ang);
-        vec3 rdir = d * ca
-                  + cross(NS_POLE, d) * sa
-                  + NS_POLE * dot(NS_POLE, d) * (1.0 - ca);
-
-        vec3 sky = nightSky(rdir, uint(uParamB));
+        vec3 sky = nightSky(normalize(vDir), uint(uParamB));
         // Additive pipeline (forced for this draw): rgb adds over the dome.
         fragColor = vec4(sky * night, 1.0);
         return;

src/AcDream.App/Rendering/Shaders/sky.vert

@@ -67,10 +67,6 @@ layout(std140, ACDREAM_UBO_SET binding = 4) uniform SkyParams {
     vec2  uUvScroll;
     float uApplyFog;      // 1 for foggable layers; raw-additive keeps fog off
     float uSurfOpacity;   // final surface opacity multiplier from the CPU
-    float uNightSkyRotationTurns; // enhanced night sky (IA-26): sky rotation
-    float uNsPadA;
-    float uNsPadB;
-    float uNsPadC;
 };
 
 // Shared SceneLighting UBO — we need uFogParams.xy (fog start/end) to

src/AcDream.App/Rendering/Shaders/spv/shaders.manifest.json

@@ -311,12 +311,12 @@
       "stages": [
         {
           "stage": "vert",
-          "sourceSha256": "80c190d5544433bd6b08810c1e5040cec5090fe91839f436728d5454ed7f3c31",
+          "sourceSha256": "9102b156bd4fd667831353640b2feee2ddde66e88579a4e425566c9b67304b64",
           "compiled": true
         },
         {
           "stage": "frag",
-          "sourceSha256": "76481dcc1a321c65308bf9c081254978ee7f12413166df5d32a1606228bdc768",
+          "sourceSha256": "e7ccdb4d5fece2ceeb48eb43aaa827424df2b68614987eeb3dfb7880dff8ea83",
           "compiled": true
         }
       ]