Fixed terrain cleanup

src/features/editScene/TerrainRequirements.md

@@ -1219,6 +1219,13 @@ draw off by default with toggle; removing and re-adding terrain is leak-free.
 
 ### Milestone 3 — Serialization + heightmap editing + splat painting
 - Scene serialization for `TerrainComponent` (save/load JSON round-trip).
+
+**Terrain cleanup on entity/component removal** (added post-M2):
+`TerrainSystem::update()` now tracks whether any matching terrain entity exists.
+If `m_active` is true but the query returns no entity (because the terrain
+entity was deleted or its TerrainComponent was removed), `deactivate()` is
+called automatically.  Without this, removing the component or deleting the
+entity would leave the terrain and colliders orphaned in the scene.
 - Binary heightmap file save/load alongside scene JSON.
 - Brush tools (raise/lower/smooth/flatten) with curve-based brush profile.
 - Splat paint brush (select layer, set opacity, paint blend values via

src/features/editScene/systems/TerrainSystem.cpp

@@ -411,9 +411,11 @@ void TerrainSystem::deactivate()
 
 void TerrainSystem::update(float /*deltaTime*/)
 {
+	bool found = false;
 	m_terrainQuery.each([&](flecs::entity e, TerrainComponent &tc,
 				TransformComponent &xform) {
 		(void)e;
+			found = true;
 		if (!tc.enabled && m_active) {
 			deactivate();
 			return;
@@ -422,6 +424,10 @@ void TerrainSystem::update(float /*deltaTime*/)
 			activate(tc, xform);
 	});
 
+	/* If the terrain entity or its component was removed, tear down. */
+	if (m_active && !found)
+		deactivate();
+
 	if (m_active && mTerrainGroup)
 		mTerrainGroup->update(false);