basic ECS spawner

addons/gecs/tests/systems/o_health_observer.gd

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+## Observer that watches C_ObserverHealth component with a query filter
+class_name O_HealthObserver
+extends Observer
+
+var health_changed_count: int = 0
+var health_added_count: int = 0
+var health_removed_count: int = 0
+var low_health_alerts: Array[Entity] = []
+
+func watch() -> Resource:
+	return C_ObserverHealth
+
+func match() -> QueryBuilder:
+	# Only watch entities that have both C_ObserverHealth and C_ObserverTest
+	return q.with_all([C_ObserverHealth, C_ObserverTest])
+
+func on_component_added(entity: Entity, component: Resource) -> void:
+	health_added_count += 1
+
+func on_component_removed(entity: Entity, component: Resource) -> void:
+	health_removed_count += 1
+
+func on_component_changed(
+	entity: Entity, component: Resource, property: String, new_value: Variant, old_value: Variant
+) -> void:
+	if property == "health":
+		health_changed_count += 1
+		# Track entities with low health
+		if new_value < 30:
+			if not low_health_alerts.has(entity):
+				low_health_alerts.append(entity)
+
+func reset() -> void:
+	health_changed_count = 0
+	health_added_count = 0
+	health_removed_count = 0
+	low_health_alerts.clear()