Measure session object identity and listener counts across engine switches

window.__gevSession names each session object by a stable instance id and counts applications, attachments and detaches. scripts/qa-app-once.mjs (report-only with --report for now) runs three round trips and a parked-renderer rollback on a keyless preview with paid map, model and voice endpoints blocked.

scripts/qa-app-once.mjs

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+// The application is created once per page: switching engines detaches and
+// attaches only the engine-bound parts. This gate runs three Cesium→Navara→
+// Cesium round trips and checks that every session object keeps its identity,
+// an open panel, typed text and the focused field survive, Escape still does
+// what it did before the switches, window/document listeners do not grow,
+// and a failed candidate rolls back onto the same session objects.
+//
+// node scripts/qa-app-once.mjs http://127.0.0.1:<port>/ [--report]
+// `--report` prints the measurements without asserting them.
+import assert from 'node:assert/strict';
+import {
+  idDifference,
+  launch,
+  listenerCounts,
+  listenerDifference,
+  openSessionPage,
+  previewBase,
+  readSession,
+  requestEngine,
+  sessionAddress,
+  switchEngine,
+  waitReady,
+} from './qa/appSessionHarness.mjs';
+
+const base = previewBase(process.argv[2]);
+const reportOnly = process.argv.includes('--report');
+const report = { switches: [], failures: [] };
+const check = (condition, message, detail) => {
+  if (condition) return;
+  report.failures.push({ message, detail });
+  if (!reportOnly)
+    assert.fail(`${message}${detail ? ` ${JSON.stringify(detail)}` : ''}`);
+};
+
+const FIELD = '#location-search';
+const PANEL = 'data-panel';
+
+// The page's visible UI state the switches must leave alone.
+const readUi = (page) =>
+  page.evaluate(
+    (field, panel) => ({
+      value: document.querySelector(field)?.value ?? null,
+      focused: document.activeElement?.id || null,
+      panelOpen: !document
+        .getElementById(panel)
+        ?.classList.contains('collapsed'),
+    }),
+    FIELD,
+    PANEL,
+  );
+
+// Focus the field, press Escape and read what changed; then put the state
+// back. The same press before and after the switches must have the same
+// effect.
+async function escapeEffect(page) {
+  await page.focus(FIELD);
+  const before = await readUi(page);
+  await page.keyboard.press('Escape');
+  await new Promise((resolve) => setTimeout(resolve, 400));
+  const after = await readUi(page);
+  return { before, after };
+}
+
+async function prepareUi(page) {
+  await page.evaluate((panel) => {
+    const style = window.__godsEyeView.styleManager;
+    style.setPanelCollapsed(panel, false, { explicit: true });
+    style.setPanelCollapsed('location-bar', false, { explicit: true });
+  }, PANEL);
+  await page.waitForFunction(
+    (field) => document.querySelector(field)?.offsetParent !== null,
+    {},
+    FIELD,
+  );
+  await page.evaluate((field) => {
+    const input = document.querySelector(field);
+    input.focus();
+    input.value = 'Reykjav';
+    input.dispatchEvent(new Event('input', { bubbles: true }));
+  }, FIELD);
+}
+
+const browser = await launch();
+try {
+  const { page, errors } = await openSessionPage(
+    browser,
+    sessionAddress(base, { engine: 'cesium' }),
+  );
+  await waitReady(page, 'cesium');
+  // Let the first boot's deferred listeners land before counting.
+  await new Promise((resolve) => setTimeout(resolve, 2000));
+  const boot = await readSession(page);
+  const bootListeners = await listenerCounts(page);
+  report.boot = boot;
+
+  await prepareUi(page);
+  const escapeBefore = await escapeEffect(page);
+  report.escapeBefore = escapeBefore;
+  await prepareUi(page);
+  const uiBefore = await readUi(page);
+  report.uiBefore = uiBefore;
+
+  const sequence = ['navara', 'cesium', 'navara', 'cesium', 'navara', 'cesium'];
+  for (const kind of sequence) {
+    const started = Date.now();
+    await switchEngine(page, kind);
+    const state = await readSession(page);
+    const ui = await readUi(page);
+    if (kind === 'navara')
+      await page.evaluate(() => {
+        window.__qaParkedNavara = window.__godsEyeView.engine;
+      });
+    if (report.switches.length === 1)
+      report.firstRoundTripListeners = listenerDifference(
+        bootListeners,
+        await listenerCounts(page),
+      );
+    report.switches.push({
+      kind,
+      ms: Date.now() - started,
+      ids: idDifference(boot.ids, state.ids),
+      counters: state.counters,
+      ui,
+    });
+    check(
+      Object.keys(idDifference(boot.ids, state.ids)).length === 0,
+      `session ids changed on the switch to ${kind}`,
+      idDifference(boot.ids, state.ids),
+    );
+    check(
+      ui.value === uiBefore.value,
+      `typed text lost on the switch to ${kind}`,
+      ui,
+    );
+    check(ui.panelOpen, `open panel closed on the switch to ${kind}`, ui);
+    check(
+      ui.focused === uiBefore.focused,
+      `focus moved on the switch to ${kind}`,
+      ui,
+    );
+  }
+  await new Promise((resolve) => setTimeout(resolve, 2000));
+  const after = await readSession(page);
+  const afterListeners = await listenerCounts(page);
+  report.after = after;
+  report.listeners = listenerDifference(bootListeners, afterListeners);
+  check(
+    Object.keys(report.listeners).length === 0,
+    'window/document listeners changed after three round trips',
+    report.listeners,
+  );
+  check(
+    after.counters?.attachments === 1 + sequence.length &&
+      after.counters?.detaches === sequence.length,
+    'each switch detaches once and attaches once',
+    after.counters,
+  );
+  check(
+    after.counters?.applications === 1,
+    'the application must be created once',
+    after.counters,
+  );
+
+  const escapeAfter = await escapeEffect(page);
+  report.escapeAfter = escapeAfter;
+  check(
+    JSON.stringify(escapeAfter) === JSON.stringify(escapeBefore),
+    'Escape behaves differently after the switches',
+    { escapeBefore, escapeAfter },
+  );
+
+  // A failed candidate: the parked Navara renderer refuses to resume (as in
+  // qa-layer-handoff.mjs). The working Cesium attaches again on the same
+  // session objects.
+  await prepareUi(page);
+  const beforeRollback = await readSession(page);
+  const historyLength = await page.evaluate(() => history.length);
+  await page.evaluate(() => {
+    window.__qaRollback = false;
+    const parked = window.__qaParkedNavara;
+    const request = parked.render.request;
+    parked.render.request = function (...args) {
+      parked.render.request = request;
+      window.__qaRollback = true;
+      throw new Error('QA parked renderer failure');
+    };
+  });
+  const sabotaged = true;
+  if (sabotaged) {
+    await requestEngine(page, 'navara');
+    await page.waitForFunction(() => window.__qaRollback === true, {
+      timeout: 60_000,
+    });
+    await waitReady(page, 'cesium');
+    const rolledBack = await readSession(page);
+    const ui = await readUi(page);
+    report.rollback = {
+      ids: idDifference(beforeRollback.ids, rolledBack.ids),
+      counters: rolledBack.counters,
+      ui,
+      history: (await page.evaluate(() => history.length)) - historyLength,
+    };
+    check(
+      Object.keys(report.rollback.ids).length === 0,
+      'a rollback changed session ids',
+      report.rollback,
+    );
+    check(
+      report.rollback.history === 0,
+      'a rollback added a history entry',
+      report.rollback,
+    );
+    check(
+      ui.value === uiBefore.value && ui.panelOpen,
+      'a rollback lost the UI state',
+      ui,
+    );
+    // The page still switches after the rollback.
+    await switchEngine(page, 'navara');
+    await switchEngine(page, 'cesium');
+    const final = await readSession(page);
+    check(
+      Object.keys(idDifference(boot.ids, final.ids)).length === 0,
+      'ids changed after the rollback',
+      idDifference(boot.ids, final.ids),
+    );
+  }
+  report.errors = errors;
+  check(errors.length === 0, 'page errors', errors);
+  console.log(JSON.stringify(report, null, 2));
+  if (!reportOnly) console.log('PASS application created once; session kept');
+} finally {
+  await browser.close();
+}