basic ECS spawner

addons/gecs/tests/systems/o_observer_test.gd

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+## Observer that watches C_ObserverTest component for add/remove/change events
+class_name O_ObserverTest
+extends Observer
+
+var added_count: int = 0
+var removed_count: int = 0
+var changed_count: int = 0
+var last_added_entity: Entity = null
+var last_removed_entity: Entity = null
+var last_changed_entity: Entity = null
+var last_changed_property: String = ""
+var last_old_value: Variant = null
+var last_new_value: Variant = null
+
+func watch() -> Resource:
+	return C_ObserverTest
+
+func match() -> QueryBuilder:
+	# Match all entities with C_ObserverTest
+	return q.with_all([C_ObserverTest])
+
+func on_component_added(entity: Entity, component: Resource) -> void:
+	added_count += 1
+	last_added_entity = entity
+
+func on_component_removed(entity: Entity, component: Resource) -> void:
+	removed_count += 1
+	last_removed_entity = entity
+
+func on_component_changed(
+	entity: Entity, component: Resource, property: String, new_value: Variant, old_value: Variant
+) -> void:
+	changed_count += 1
+	last_changed_entity = entity
+	last_changed_property = property
+	last_old_value = old_value
+	last_new_value = new_value
+
+func reset() -> void:
+	added_count = 0
+	removed_count = 0
+	changed_count = 0
+	last_added_entity = null
+	last_removed_entity = null
+	last_changed_entity = null
+	last_changed_property = ""
+	last_old_value = null
+	last_new_value = null