Improve failover startup handling and status UI

test/server/connection-service.test.js

@@ -364,7 +364,9 @@ test('selector activation failure rolls runtime and config back before applied t
     },
   });
   const before = harness.snapshot();
-  await assert.rejects(harness.service.restart(), /selector failed/);
+  await assert.rejects(harness.service.restart(), (error) => (
+    error.code === 'PROCESS_START_FAILED' && error.cause?.message === 'selector failed'
+  ));
   assert.deepEqual(domain(harness.snapshot()), domain(before));
   assert.equal(harness.events.includes('state.update'), false);
   assert.deepEqual(harness.events.filter((event) => event.startsWith('selector.')), ['selector.primary', 'selector.primary']);

test/server/singbox-selector-service.test.js

@@ -0,0 +1,19 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+
+import { createSingboxSelectorService } from '../../dist/server/services/singboxSelectorService.js';
+
+test('selector waits for the sing-box API after a fresh process start', async () => {
+  let attempts = 0;
+  const service = createSingboxSelectorService({
+    port: 0,
+    send: async (method) => {
+      attempts += 1;
+      if (attempts < 3) throw Object.assign(new Error('not ready'), { code: 'ECONNREFUSED' });
+      return method === 'GET' ? { now: 'channel-primary' } : {};
+    },
+  });
+
+  assert.deepEqual(await service.select('primary'), { role: 'primary' });
+  assert.equal(attempts, 4);
+});