Flush pending standalone dev-source autosaves on pagehide

[Copilot]

The standalone dev editor persisted source changes with a debounce, which could drop the most recent edits if the page was reloaded or closed before the timer fired. This updates the dev harness to flush pending autosave state during pagehide.

• Autosave flush on unload

  • Track the latest unsaved editor source per standalone editor instance.
  • Flush any pending debounced localStorage write when the page is being hidden.

• Keep existing debounce behavior

  • Preserve the current debounced save path during normal editing.
  • Clear pending state after either the scheduled save or the pagehide flush runs.

• Scope

  • Change is limited to the standalone dev harness in packages/standalone/src/test-main.tsx.

window.addEventListener("pagehide", () => {
  for (const [key, source] of pendingSources) {
    const pending = saveTimers.get(key);
    if (pending !== undefined) {
      window.clearTimeout(pending);
      saveTimers.delete(key);
    }
    localStorage.setItem(key, source);
  }
  pendingSources.clear();
});