Put dead matadors on a corpse collision layer

A killed matador's ragdoll shared the WORLD layer with the bull, so the
bull collided with the bodies and spazzed out on them. Give corpses a
dedicated CORPSE layer masked to itself, and tag the ground/walls with
CORPSE too (at level load, so it also reaches colliders baked into the
instanced GLB arenas). The corpse still rests on the arena, but the bull
— which only masks WORLD — passes straight through the bodies.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

levels/game_shell.gd

@@ -4,6 +4,8 @@ extends Node3D
 ## spawners, lighting, colliders) into LevelRoot. Switching levels frees the whole
 ## previous module first, so no old mesh or collider can survive into the next fight.
 
+const PhysicsLayers = preload("res://physics_layers.gd")
+
 @onready var _level_root: Node3D = $LevelRoot
 @onready var _camera: IsoCamera = $Player/Camera3D
 
@@ -25,4 +27,16 @@ func load_active_level() -> void:
 		push_warning("game_shell: active level has no level_scene")
 		return
 	_camera.set_framing_scale(level.camera_zoom)
-	_level_root.add_child(level.level_scene.instantiate())
+	var module := level.level_scene.instantiate()
+	_tag_environment_for_corpses(module)
+	_level_root.add_child(module)
+
+
+## Ground and walls stay on WORLD so the bull and live matadors collide with them; here
+## we add CORPSE too. A killed matador's ragdoll is masked to CORPSE alone, so it rests
+## on the arena while the bull — which only collides with WORLD — passes through the body
+## instead of spazzing out on it. Done at load so it also reaches colliders baked into
+## the instanced GLB arenas, not just the level module's own floor box.
+func _tag_environment_for_corpses(module: Node) -> void:
+	for body: StaticBody3D in module.find_children("*", "StaticBody3D", true, false):
+		body.collision_layer |= PhysicsLayers.CORPSE