fix(render): A7 Fix D D-3/D-4 — two-path lighting (objects plain-Lambert+sun, EnvCell wrap+no-sun) (#140)

mesh_modern unified all meshes into one calc_point_light path: it applied the
bake's half-Lambert wrap to objects (lighting character backs from a torch behind
them) and added the sun to EnvCell building shells (warm facade wash). Retail
splits these: objects = hardware plain Lambert max(0,N.L) + sun; EnvCell walls =
baked wrap, dynamics only, NO sun (minimize_envcell_lighting). Add a per-draw
uLightingMode (WbDrawDispatcher=0 object, EnvCellRenderer=1 envcell) selecting the
angular term (wrap vs plain Lambert) and gating the sun. Per-light cap + D-1 clamp
unchanged.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

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

@@ -122,6 +122,7 @@ uniform mat4 uViewProjection;
 // _opaqueDrawCount before the transparent MDI call, matching WorldBuilder's
 // uDrawIDOffset pattern in BaseObjectRenderManager.cs line 845.
 uniform int uDrawIDOffset;
+uniform int uLightingMode;   // A7 Fix D: 0 = OBJECT (plain Lambert + sun), 1 = ENVCELL (half-Lambert wrap, no sun)
 
 // SceneLighting UBO — binding=1 in the UBO namespace (GL keeps the SSBO and UBO
 // binding tables separate, so this coexists with the binding=1 BatchBuffer SSBO
@@ -157,16 +158,19 @@ vec3 pointContribution(vec3 N, vec3 worldPos, GlobalLight L) {
     float d      = sqrt(distsq);
     float range  = L.dirAndRange.w;               // falloff_eff = Falloff × 1.3
     if (d >= range || range <= 1e-4) return vec3(0.0);
-    // Half-Lambert WRAP: (1/1.5)·(N·D + 0.5·d). N·D = d·cosθ (D un-normalised); the
-    // +0.5·d bias lets a face angled AWAY from the torch still catch light (retail's
-    // soft terminator). wrap≤0 = fully shadowed. TwoLpr=1.5, WrapBias=0.5.
-    float wrap = (1.0 / 1.5) * (dot(N, toL) + 0.5 * d);
-    if (wrap <= 0.0) return vec3(0.0);
+    // A7 Fix D D-3: angular term by lighting path. ENVCELL bake (mode 1) keeps the
+    // half-Lambert wrap (lights surfaces angled away, retail calc_point_light); OBJECT
+    // mode (0) uses plain Lambert max(0,N·L) so a torch BEHIND a character contributes
+    // nothing (retail's hardware path). toL is un-normalised (length d).
+    float angular = (uLightingMode == 1)
+        ? (1.0 / 1.5) * (dot(N, toL) + 0.5 * d)   // half-Lambert wrap (EnvCell bake)
+        : max(0.0, dot(N, toL));                  // plain Lambert (object/hardware)
+    if (angular <= 0.0) return vec3(0.0);
     // NORM branch (distance-cube): >1 m → distsq·d ≈ inverse-square soft far halo;
     // <1 m → just d (dodge the near singularity). "Punchy near, soft far."
     float norm      = (distsq > 1.0) ? (distsq * d) : d;
     float intensity = L.colorAndIntensity.w;
-    float scale     = (1.0 - d / range) * intensity * (wrap / norm);
+    float scale     = (1.0 - d / range) * intensity * (angular / norm);
     if (kind == 2) {
         // Spotlight: hard-edged cos-cone gate layered on the point ramp.
         vec3 Ldir = toL / max(d, 1e-4);
@@ -183,15 +187,18 @@ vec3 pointContribution(vec3 N, vec3 worldPos, GlobalLight L) {
 vec3 accumulateLights(vec3 N, vec3 worldPos, int instanceIndex) {
     vec3 lit = uCellAmbient.xyz;
 
-    // SUN / directional — material-lit term (added with ambient, NOT into the
-    // torch sum), unchanged.
-    int activeLights = int(uCellAmbient.w);
-    for (int i = 0; i < 8; ++i) {
-        if (i >= activeLights) break;
-        if (int(uLights[i].posAndKind.w) != 0) continue;   // directional only
-        vec3 Ldir = -uLights[i].dirAndRange.xyz;
-        float ndl = max(0.0, dot(N, Ldir));
-        lit += uLights[i].colorAndIntensity.xyz * uLights[i].colorAndIntensity.w * ndl;
+    // SUN / directional — OBJECT path only (mode 0). retail's EnvCell path
+    // (minimize_envcell_lighting) enables only dynamic lights, NEVER the sun, so
+    // EnvCell walls (mode 1) get no directional sun wash (A7 Fix D D-4).
+    if (uLightingMode == 0) {
+        int activeLights = int(uCellAmbient.w);
+        for (int i = 0; i < 8; ++i) {
+            if (i >= activeLights) break;
+            if (int(uLights[i].posAndKind.w) != 0) continue;   // directional only
+            vec3 Ldir = -uLights[i].dirAndRange.xyz;
+            float ndl = max(0.0, dot(N, Ldir));
+            lit += uLights[i].colorAndIntensity.xyz * uLights[i].colorAndIntensity.w * ndl;
+        }
     }
 
     // POINT / SPOT torches: their OWN accumulator (A7 Fix D, D-1). Retail's

src/AcDream.App/Rendering/Wb/EnvCellRenderer.cs

@@ -877,6 +877,7 @@ public sealed unsafe class EnvCellRenderer : IDisposable
             // WB EnvCellRenderManager.cs:406-409: uniform state setup.
             _shader.SetInt("uRenderPass", (int)renderPass);
             _shader.SetInt("uFilterByCell", 0);
+            _shader.SetInt("uLightingMode", 1);   // A7 Fix D D-3/D-4: EnvCell bake (wrap points, no sun)
 
             // Phase U.4 ROOT-CAUSE FIX (cell-shell flicker / "transparent walls when
             // moving"): upload uViewProjection HERE rather than inheriting it from

src/AcDream.App/Rendering/Wb/WbDrawDispatcher.cs

@@ -893,6 +893,9 @@ public sealed unsafe class WbDrawDispatcher : IDisposable
         _indoorProbeFrameCounter++;
         var vp = camera.View * camera.Projection;
         _shader.SetMatrix4("uViewProjection", vp);
+        // A7 Fix D D-3/D-4: object path — plain Lambert points + sun. MUST set
+        // explicitly (shared GL uniform; EnvCellRenderer sets it to 1).
+        _shader.SetInt("uLightingMode", 0);
 
         // #128 self-heal: fresh re-request dedup per Draw pass.
         _missRequested.Clear();