Hot-reload simulation

// Hot-reload pattern with FileSystemObserver
const opfsRoot  = await navigator.storage.getDirectory();
const fileHandle = await opfsRoot.getFileHandle('index.md', { create: true });

const observer = new FileSystemObserver(async (records) => {
  for (const record of records) {
    if (record.type === 'modified') {
      // File changed — re-read and re-render
      const file = await fileHandle.getFile();
      const text = await file.text();
      renderMarkdown(text);
      showReloadFlash();  // green flash like browser devtools reload
    }
  }
});

await observer.observe(fileHandle);

// Editor save path
async function saveFile() {
  const writable = await fileHandle.createWritable();
  await writable.write(editor.value);
  await writable.close();
  // Observer fires automatically with { type: 'modified' }
}