feat(framework): core 响应式 signal 基元(自研薄封装)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

cocoscreator_projects/YouleNexus/assets/framework/core/reactive.ts

@@ -0,0 +1,31 @@
+export type Unsubscribe = () => void;
+
+export interface ReadonlyReactive<T> {
+  readonly value: T;
+  subscribe(fn: (value: T, prev: T) => void): Unsubscribe;  // 返回退订函数
+}
+
+export interface Reactive<T> extends ReadonlyReactive<T> {
+  value: T;   // 可写
+}
+
+/** 极小响应式信号：value 读写 + 订阅。Object.is 判等(值未变不通知)；订阅者抛错隔离。 */
+export function signal<T>(initial: T): Reactive<T> {
+  let current = initial;
+  const subs = new Set<(value: T, prev: T) => void>();
+  return {
+    get value(): T { return current; },
+    set value(v: T) {
+      if (Object.is(v, current)) return;
+      const prev = current;
+      current = v;
+      for (const fn of [...subs]) {
+        try { fn(current, prev); } catch (e) { console.error('[reactive] subscriber error:', e); }
+      }
+    },
+    subscribe(fn: (value: T, prev: T) => void): Unsubscribe {
+      subs.add(fn);
+      return () => { subs.delete(fn); };
+    },
+  };
+}