fix(render3d): a lake can be the mirrored water, with its own wet shore

A reflecting body is clipped to its ellipse like every other unless it is an
unbounded sea, so a map whose reflection belongs to its lake (Maroon Lake, once
its sea sits below it) does not draw that lake's level over every hollow in the
survey. The terrain's wet shore and its forest and scree gates read the carved
lake's line inside its outline (u_lake), the rule grass already used. SPIR-V
regenerated.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

packages/ludic.render3d/shaders/terrain.frag

@@ -19,6 +19,15 @@ uniform float u_carpet_on;
 uniform float u_snow_line;
 uniform float u_lake_level;      // the ground just above the water is wet and dark
 uniform float u_sea_level;       // the sea's line: shore, forest and scree gates (terrain_sea)
+uniform vec4 u_lake;             // the carved lake's outline: centre x/z, half extents (zero = none)
+// The water line that applies here: the sea everywhere, the lake's own inside its outline -
+// the rule the grass and the game's water test use. One line for both put a lake above the
+// sea with no wet shore and forest painted down its bed.
+float waterLine(vec2 xz) {
+  float wl = u_sea_level;
+  if (u_lake.z > 0.0) { vec2 q = (xz - u_lake.xy) / u_lake.zw;  if (dot(q, q) < 1.0) wl = max(wl, u_lake_level); }
+  return wl;
+}
 uniform vec2 u_origin;           // world offset of the terrain grid
 
 // The ground's own sun shadow comes from the baked height-field map (tershadow.frag),
@@ -251,14 +260,14 @@ vec3 groundShade(vec3 p, vec3 N, float slope, float dist, float viewDepth, bool
     vec3 ocf = textureLod(u_ortho, v_huv, 2.0).rgb;
     float gx = ocf.g - max(ocf.r, ocf.b);
     // (the photograph is sampled linear: sRGB 72 is 0.06, 92 is 0.11)
-    forestW = smoothstep(0.12, 0.06, max(ocf.r, max(ocf.g, ocf.b))) * smoothstep(0.004, 0.012, gx) * smoothstep(u_sea_level + 0.8, u_sea_level + 1.8, p.y);
+    forestW = smoothstep(0.12, 0.06, max(ocf.r, max(ocf.g, ocf.b))) * smoothstep(0.004, 0.012, gx) * smoothstep(waterLine(p.xz) + 0.8, waterLine(p.xz) + 1.8, p.y);
     // Classify from a ~60 m blur, never from the pixels: the survey's 10 m pixels carry
     // a foot trail as a broken line of bare ground, and thresholding them painted it
     // across the meadow as tan dashes (and, on the CPU, lined boulders up along it).
     vec3 ocl = textureLod(u_ortho, v_huv, 2.5).rgb;
     float mxc = max(ocl.r, max(ocl.g, ocl.b)), mnc = min(ocl.r, min(ocl.g, ocl.b));
     float greenEx = ocl.g - max(ocl.r, ocl.b);
-    screeC = smoothstep(0.008, -0.002, greenEx) * smoothstep(0.06, 0.12, mxc) * (1.0 - smoothstep(0.55, 0.75, mxc)) * smoothstep(u_sea_level + 0.2, u_sea_level + 1.2, p.y);
+    screeC = smoothstep(0.008, -0.002, greenEx) * smoothstep(0.06, 0.12, mxc) * (1.0 - smoothstep(0.55, 0.75, mxc)) * smoothstep(waterLine(p.xz) + 0.2, waterLine(p.xz) + 1.2, p.y);
     snowC = smoothstep(0.08, 0.04, mxc - mnc) * smoothstep(0.55, 0.8, mxc);
   }
   // snow lingering in the high gullies is drawn further down, but whether it can be
@@ -377,7 +386,7 @@ vec3 groundShade(vec3 p, vec3 N, float slope, float dist, float viewDepth, bool
   // the bank here: identical noise fields, identical time, identical phase, keyed off
   // height above the lake instead of depth below it. Across the seam the two agree, so
   // there is nothing there to read as an edge.
-  float above = p.y - u_sea_level;                        // >0 on land, metres
+  float above = p.y - waterLine(p.xz);                    // >0 on land, metres
   // wet ground: darker and glossier near the water, fading out over ~1.2 m
   float wet = smoothstep(1.2, 0.0, above);
   alb *= mix(1.0, 0.5, wet * 0.85);