GAS『DriveApp cannot be used in this context』の原因と対処法

// ❌ カスタム関数内でDriveAppを呼ぶ（禁止文脈）
function LIST_FILES(folderId) {
  // return DriveApp.getFolderById(folderId).getFiles(); // ここでエラー
}

// ✅ メニューや手動実行・時間トリガーで動かす
function listFilesToSheet(folderId, sheetId, sheetName) {
  const sh = SpreadsheetApp.openById(sheetId).getSheetByName(sheetName);
  const it = DriveApp.getFolderById(folderId).getFiles();
  const out = [];
  while (it.hasNext()) {
    const f = it.next();
    out.push([f.getName(), f.getId(), f.getUrl(), f.getSize()]);
  }
  sh.clearContents();
  if (out.length) sh.getRange(1,1,out.length,4).setValues(out);
}

function onOpen() {
  SpreadsheetApp.getUi().createMenu('DriveOps')
    .addItem('フォルダ一覧を書き出す', 'runList')
    .addToUi();
}
function runList() {
  listFilesToSheet('YOUR_FOLDER_ID','YOUR_SHEET_ID','Data');
}

function job(e) {
  // DriveApp利用OK（トリガー作成者の認可で実行）
  const name = DriveApp.getFileById('YOUR_FILE_ID').getName();
  const sh = SpreadsheetApp.getActive().getSheetByName('Log');
  sh.appendRow([new Date(), name, e?.range?.getA1Notation() || '']);
}

function installOnEdit() {
  ScriptApp.newTrigger('job')
    .forSpreadsheet(SpreadsheetApp.getActive())
    .onEdit()
    .create();
}

// Code.gs
function createFileInFolder(folderId, name, content) {
  const file = DriveApp.getFolderById(folderId).createFile(name, content, MimeType.PLAIN_TEXT);
  return { id: file.getId(), url: file.getUrl() };
}
function doGet(){ return HtmlService.createHtmlOutputFromFile('index'); }

<!-- index.html -->
<input id="name" placeholder="file.txt">
<button onclick="run()">作成</button>
<script>
function run(){
  const n = document.getElementById('name').value || 'file.txt';
  google.script.run
    .withSuccessHandler(res => alert('作成: ' + res.url))
    .withFailureHandler(err => alert('失敗: ' + (err && err.message)))
    .createFileInFolder('YOUR_FOLDER_ID', n, 'hello');
}
</script>

function diagDrive(targetId) {
  const ctx = {
    effective: Session.getEffectiveUser().getEmail(),
    active: Session.getActiveUser().getEmail()
  };
  try {
    const f = DriveApp.getFileById(targetId);
    console.log('OK', { ctx, name: f.getName(), url: f.getUrl() });
    return true;
  } catch (e) {
    console.error('Drive diag failed', { ctx, msg: e.message });
    throw e;
  }
}