feat: add structured economic events

tests/simulation_state_serialization_test.gd

@@ -11,6 +11,7 @@ func _run() -> void:
 	_test_legacy_npc_migration()
 	_test_legacy_resource_migration()
 	_test_legacy_world_storage_migration()
+	_test_previous_world_event_migration()
 	_test_schema_rejection()
 
 	if failures.is_empty():
@@ -203,6 +204,24 @@ func _test_legacy_world_storage_migration() -> void:
 		)
 	manager.free()
 
+func _test_previous_world_event_migration() -> void:
+	var manager := _create_manager(56)
+	var previous_data: Dictionary = manager.create_state_record().to_dictionary()
+	previous_data["schema_version"] = (
+		SimulationStateRecord.PREVIOUS_SCHEMA_VERSION
+	)
+	previous_data.erase("economic_events")
+	previous_data["simulation"].erase("next_event_id")
+	var migrated := SimulationStateRecord.from_dictionary(previous_data)
+	_check(migrated != null, "World schema v2 should add an empty event stream")
+	if migrated != null:
+		_check(
+			migrated.economic_events.is_empty()
+			and int(migrated.simulation["next_event_id"]) == 0,
+			"World v2 migration should initialize deterministic event identity"
+		)
+	manager.free()
+
 func _create_manager(seed_value: int) -> Node:
 	var manager: Node = load("res://simulation/SimulationManager.gd").new()
 	manager.simulation_seed = seed_value