Harden traffic history worker lifecycle and query performance

test/web/app-shell-contract.test.js

@@ -1,6 +1,7 @@
 import assert from 'node:assert/strict';
 import { readFileSync } from 'node:fs';
 import test from 'node:test';
+import { parse } from '@babel/parser';
 
 const index = readFileSync(new URL('../../index.html', import.meta.url), 'utf8');
 const main = readFileSync(new URL('../../src/web/main.tsx', import.meta.url), 'utf8');
@@ -23,3 +24,44 @@ test('App remains the exported composition component without bootstrap side effe
   assert.match(app, /<ClientOverviewPage/);
   assert.match(app, /<StaleBanner/);
 });
+
+test('state polling waits for completion and stops after cleanup', async (t) => {
+  const compiled = readFileSync(new URL('../../.test-dist/src/web/App.js', import.meta.url), 'utf8');
+  const component = parse(compiled, { sourceType: 'module' }).program.body
+    .find((node) => node.declaration?.id?.name === 'App').declaration;
+  const effect = component.body.body.map((node) => node.expression)
+    .filter((node) => node?.callee?.name === 'useEffect')
+    .map((node) => node.arguments[0])
+    .find((node) => compiled.slice(node.start, node.end).includes('loadState('));
+  // Execute the shipped effect with a deferred request; no DOM or copied polling loop.
+  const setup = new Function('loadState', `return (${compiled.slice(effect.start, effect.end)})`);
+  t.mock.timers.enable({ apis: ['setTimeout', 'setInterval'] });
+  let calls = 0;
+  let finish;
+  const start = setup(() => {
+    calls++;
+    return new Promise((resolve) => { finish = resolve; });
+  });
+  const cleanup = start();
+  assert.equal(calls, 1);
+  t.mock.timers.tick(40_000);
+  assert.equal(calls, 1);
+  finish();
+  await Promise.resolve();
+  t.mock.timers.tick(4_999);
+  assert.equal(calls, 1);
+  t.mock.timers.tick(1);
+  assert.equal(calls, 2);
+  cleanup();
+  finish();
+  await Promise.resolve();
+  t.mock.timers.tick(40_000);
+  assert.equal(calls, 2);
+
+  const cleanupScheduled = start();
+  finish();
+  await Promise.resolve();
+  cleanupScheduled();
+  t.mock.timers.tick(40_000);
+  assert.equal(calls, 3);
+});