fix(playable): close release validation lifecycle gaps

project/playable_harness_test.gd

@@ -203,10 +203,24 @@ func valid_config() -> Dictionary:
 		"resolution": [1280, 720], "loops": 1, "timeout_seconds": 900,
 	}
 
+func test_probe_releases_old_registries() -> void:
+	var observer := Probe.new()
+	for i in range(30):
+		var registry := FakeFx.new()
+		var reference: WeakRef = weakref(registry)
+		observer.watch_local(registry, "fx_spawned", "fx_spawned")
+		observer.watch_local(registry, "fx_finished", "fx_finished")
+		check(observer.bound_count() == 2, "probe prunes old scene bindings")
+		registry = null
+		check(reference.get_ref() == null, "probe does not retain the old scene's effect registry")
+	observer.disconnect_all()
+	observer.free()
+
 func run() -> void:
 	MapCoord.set_base(Vector2.ZERO)
 	test_config_contract()
 	test_report_contract()
+	test_probe_releases_old_registries()
 	test_happy_path()
 	test_gameplay_not_allowed()
 	test_absent_slot_fails_without_select()