fix: align LOD biome selection with registry scoring

modules/world-worldgen/src/biome_selector.zig

@@ -258,49 +258,12 @@ pub fn selectBiomeWithConstraintsAndRiver(climate: ClimateParams, structural: St
 // LOD-optimized Biome Functions (Issue #114)
 // ============================================================================
 
-/// Simplified biome selection for LOD2+ (no structural constraints).
+/// Simplified biome selection for LOD2+ paths that only have climate params.
 ///
-/// Intentionally excludes transition micro-biomes (foothills, marsh, dry_plains,
-/// coastal_plains), special biomes (mushroom_fields, mangrove_swamp), beach,
-/// and mountain variants. These are either rare, narrow-band, or structurally
-/// dependent biomes that don't significantly affect distant terrain silhouette.
-/// The full Voronoi selection handles them when chunks enter LOD0/LOD1 range.
+/// Keep this aligned with the full registry scoring path so distant biome color
+/// and material choices use the same climate, elevation, continentalness,
+/// ruggedness, and ridge signals as LOD0 where structural height/slope filters
+/// are not available.
 pub fn selectBiomeSimple(climate: ClimateParams) BiomeId {
-    const heat = climate.temperature * 100.0;
-    const humidity = climate.humidity * 100.0;
-    const continental = climate.continentalness;
-
-    // Ocean check
-    if (continental < 0.35) {
-        if (heat <= 15) return .frozen_ocean;
-        if (heat <= 30) return .cold_ocean;
-        if (continental < 0.20) return .deep_ocean;
-        if (heat > 75 and humidity > 55) return .warm_ocean;
-        return .ocean;
-    }
-
-    if (continental < 0.48 and heat > 85 and humidity > 70) return .tropical;
-
-    // Simple land biome selection based on heat/humidity
-    if (heat < 20) {
-        return if (humidity > 50) .taiga else .snow_tundra;
-    } else if (heat < 40) {
-        return if (humidity > 60) .taiga else .plains;
-    } else if (heat < 60) {
-        return if (humidity > 70) .forest else .plains;
-    } else if (heat < 80) {
-        if (humidity > 70) {
-            return if (humidity > 85) .bamboo_jungle else .jungle;
-        }
-        if (humidity > 30) return if (climate.elevation > 0.55) .savanna_plateau else .savanna;
-        return .desert;
-    } else {
-        if (humidity > 85) return .bamboo_jungle;
-        if (humidity > 70) return .jungle;
-        if (humidity > 50) return .sparse_jungle;
-        if (humidity > 15 and humidity <= 30 and climate.elevation > 0.55) return .windswept_savanna;
-        if (humidity > 25) return .wooded_badlands;
-        if (humidity > 10) return .badlands;
-        return .desert;
-    }
+    return selectBiome(climate);
 }

modules/world-worldgen/src/biome_selector_tests.zig

@@ -591,6 +591,52 @@ test "selectBiomeSimple hot humid returns non-desert" {
     try testing.expect(biome != .ocean);
 }
 
+test "selectBiomeSimple matches constrained selector for LOD-compatible samples" {
+    const Case = struct {
+        name: []const u8,
+        climate: ClimateParams,
+        structural: StructuralParams,
+    };
+
+    const cases = [_]Case{
+        .{
+            .name = "deep ocean",
+            .climate = .{ .temperature = 0.5, .humidity = 0.5, .elevation = 0.2, .continentalness = 0.10, .ruggedness = 0.1 },
+            .structural = .{ .height = 48, .slope = 1, .continentalness = 0.10, .ridge_mask = 0.0 },
+        },
+        .{
+            .name = "plains",
+            .climate = .{ .temperature = 0.5, .humidity = 0.45, .elevation = 0.35, .continentalness = 0.60, .ruggedness = 0.1 },
+            .structural = .{ .height = 70, .slope = 2, .continentalness = 0.60, .ridge_mask = 0.1 },
+        },
+        .{
+            .name = "jagged peaks",
+            .climate = .{ .temperature = 0.32, .humidity = 0.45, .elevation = 0.85, .continentalness = 0.85, .ruggedness = 0.85, .ridge_mask = 0.7 },
+            .structural = .{ .height = 150, .slope = 18, .continentalness = 0.85, .ridge_mask = 0.7 },
+        },
+    };
+
+    for (cases) |case| {
+        errdefer std.debug.print("failed LOD selector consistency case: {s}\n", .{case.name});
+        try testing.expectEqual(selectBiomeWithConstraints(case.climate, case.structural), selectBiomeSimple(case.climate));
+    }
+}
+
+test "selectBiomeSimple uses terrain signals beyond heat and humidity" {
+    const warm_dry = ClimateParams{
+        .temperature = 0.82,
+        .humidity = 0.25,
+        .elevation = 0.40,
+        .continentalness = 0.80,
+        .ruggedness = 0.10,
+    };
+    var rugged = warm_dry;
+    rugged.ruggedness = 0.75;
+
+    try testing.expectEqual(BiomeId.savanna, selectBiomeSimple(warm_dry));
+    try testing.expectEqual(BiomeId.badlands, selectBiomeSimple(rugged));
+}
+
 // ============================================================================
 // BiomeSelection Structure Tests
 // ============================================================================

src/worldgen_tests.zig

@@ -986,13 +986,13 @@ test "BiomeSource selectBiomeSimplified returns valid biome" {
     const climate2 = biome_mod.ClimateParams{
         .temperature = 0.5,
         .humidity = 0.5,
-        .elevation = 0.4,
+        .elevation = 0.2,
         .continentalness = 0.1,
         .ruggedness = 0.2,
     };
 
     const result2 = source.selectBiomeSimplified(climate2);
-    try testing.expectEqual(result2, BiomeId.deep_ocean);
+    try testing.expectEqual(BiomeId.deep_ocean, result2);
 }
 
 test "BiomeSource getColor returns valid packed RGB" {