feat(ql3): establish 3.0 incubation baseline

packages/ql3-cluster-control/test/availability.test.cjs

@@ -0,0 +1,40 @@
+const assert = require('node:assert/strict');
+const { test } = require('node:test');
+const {
+  ClusterControlAvailabilityFence,
+} = require('@qinglong/cluster-control/availability');
+
+test('signals one bound listener exactly once without a retry path', async () => {
+  const fence = new ClusterControlAvailabilityFence();
+  const reasons = [];
+  const unsubscribe = fence.subscribe(async (error) => {
+    reasons.push(error.message);
+  });
+
+  assert.equal(fence.status, 'available');
+  assert.equal(await fence.signal(new Error('connection lost')), 'signaled');
+  assert.equal(fence.status, 'unavailable');
+  assert.equal(
+    await fence.signal(new Error('second connection lost')),
+    'already_unavailable',
+  );
+  assert.deepEqual(reasons, ['connection lost']);
+  unsubscribe();
+  unsubscribe();
+  fence.dispose();
+  assert.equal(fence.status, 'disposed');
+  assert.equal(await fence.signal(new Error('after dispose')), 'disposed');
+});
+
+test('delivers an early signal when the single application listener binds', async () => {
+  const fence = new ClusterControlAvailabilityFence();
+  assert.equal(await fence.signal(new Error('early failure')), 'signaled');
+  let reason;
+  fence.subscribe((error) => {
+    reason = error.message;
+  });
+  await Promise.resolve();
+  assert.equal(reason, 'early failure');
+  assert.throws(() => fence.subscribe(() => {}), /already bound/);
+  await assert.rejects(() => fence.signal('invalid'), /error is invalid/);
+});