feat(tools): Strata modifier quantises steep walls into ledges

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

tools/site_terrain_baker.gd

@@ -415,6 +415,45 @@ class Modifier extends RefCounted:
 		return elevation_m
 
 
+## Quantises steep ground into horizontal ledges layer_height_m apart: the stratified
+## walls of a canyon or cliff. Flat floors and summits are below minimum_slope_degrees and
+## stay untouched; the effect is full from full_slope_degrees. sharpness 0 leaves the
+## field unchanged, 1 cuts hard steps. radius_m 0 applies everywhere.
+class Strata extends Modifier:
+	var layer_height_m: float
+	var sharpness: float
+	var centre: Vector2
+	var radius_m: float
+	var _minimum_tangent: float
+	var _full_tangent: float
+
+	func _init(
+		p_layer_height_m: float,
+		p_sharpness: float,
+		p_minimum_slope_degrees: float,
+		p_full_slope_degrees: float,
+		p_centre: Vector2,
+		p_radius_m: float
+	) -> void:
+		layer_height_m = p_layer_height_m
+		sharpness = clampf(p_sharpness, 0.0, 0.999)
+		centre = p_centre
+		radius_m = p_radius_m
+		_minimum_tangent = tan(deg_to_rad(p_minimum_slope_degrees))
+		_full_tangent = tan(deg_to_rad(p_full_slope_degrees))
+
+	func modify(x_m: float, z_m: float, elevation_m: float, gradient: Vector2) -> float:
+		var weight := smoothstep(_minimum_tangent, _full_tangent, gradient.length())
+		if radius_m > 0.0:
+			weight *= 1.0 - smoothstep(radius_m * 0.8, radius_m, Vector2(x_m, z_m).distance_to(centre))
+		if weight <= 0.0:
+			return elevation_m
+		var layer := floorf(elevation_m / layer_height_m)
+		var fraction := elevation_m / layer_height_m - layer
+		var sharpened := clampf((fraction - 0.5) / (1.0 - sharpness) + 0.5, 0.0, 1.0)
+		return lerpf(elevation_m, (layer + sharpened) * layer_height_m, weight)
+
+
 class MaterialPatch extends RefCounted:
 	var centre: Vector2
 	var radius_m: float