ElyMark: a failed editor is told, leaves nothing, and can rebuild (M-13)

A failed build removes its holder. When both editors fail, the page
tells the app and keeps the text; the next mode request rebuilds it.
mark-broken.mjs breaks the editors through setAttribute and checks
the fallback, the told failures, no leftover holders and the rebuild.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/scripts/mark-broken.mjs

@@ -0,0 +1,80 @@
+// ElyMark's page: a failed editor says so (M-13).
+import { createRequire } from 'node:module'
+import { existsSync } from 'node:fs'
+import { dirname, join } from 'node:path'
+import { fileURLToPath, pathToFileURL } from 'node:url'
+
+const root = join(dirname(fileURLToPath(import.meta.url)), '../..')
+const page = join(root, 'engines/content/ely-mark/index.html')
+if (!existsSync(page)) {
+  console.log('SKIP: no page; run scripts/build-mark-content.sh')
+  process.exit(0)
+}
+let chromium
+try {
+  ;({ chromium } = createRequire(join(root, 'site/package.json'))('@playwright/test'))
+} catch {
+  console.log('SKIP: no Playwright; run pnpm install in site')
+  process.exit(0)
+}
+const fail = (why) => {
+  console.error(`FAIL: ${why}`)
+  process.exit(1)
+}
+
+const browser = await chromium.launch()
+const tab = await browser.newPage()
+await tab.addInitScript(() => {
+  window.asked = []
+  window.elyQuery = ({ request, onSuccess }) => {
+    window.asked.push(JSON.parse(request))
+    onSuccess('')
+  }
+  // Setting a role throws; `spare` keeps CodeMirror's.
+  const set = Element.prototype.setAttribute
+  window.breaks = (spare) => {
+    Element.prototype.setAttribute = function (name, value) {
+      const kept = spare && this.classList.contains('cm-content')
+      if (name === 'role' && !kept) throw new Error('broken')
+      return set.call(this, name, value)
+    }
+  }
+  window.mends = () => {
+    Element.prototype.setAttribute = set
+  }
+})
+await tab.goto(pathToFileURL(page).href)
+// What the app heard since the last look.
+let seen = 0
+const heard = async () => {
+  await tab.waitForTimeout(800)
+  const all = await tab.evaluate(() => window.asked.filter((a) => a.kind === 'shown' || a.kind === 'failed'))
+  const fresh = all.slice(seen)
+  seen = all.length
+  return JSON.stringify(fresh)
+}
+const holders = () => tab.evaluate(() => document.querySelectorAll('#document > div').length)
+const shown = () => tab.evaluate(() => document.querySelector('#document .cm-content')?.textContent ?? '')
+const open = (mode) => tab.evaluate((mode) => window.ely.open('# Kept\n', mode, {}, 1, '', null), mode)
+
+await tab.evaluate(() => window.breaks(true))
+await open('visual')
+const fell = JSON.stringify([{ kind: 'shown', mode: 'source', fallback: true, broke: 'Error' }])
+if ((await heard()) !== fell) fail('a broken visual editor did not fall back to source')
+if ((await shown()) !== '# Kept') fail(`the fallback shows ${JSON.stringify(await shown())}`)
+
+await tab.evaluate(() => window.breaks(false))
+const failed = JSON.stringify([{ kind: 'failed', generation: 1, what: 'Error' }])
+for (let n = 0; n < 3; n++) {
+  await open('visual')
+  if ((await heard()) !== failed) fail(`two broken editors, try ${n}: the app was not told`)
+}
+if ((await holders()) !== 0) fail(`failed builds left ${await holders()} holders`)
+
+await tab.evaluate(() => window.mends())
+await tab.evaluate(() => window.ely.mode('source'))
+const back = JSON.stringify([{ kind: 'shown', mode: 'source', fallback: false, broke: null }])
+if ((await heard()) !== back) fail('a mode after the failure did not rebuild')
+if ((await shown()) !== '# Kept' || (await holders()) !== 1) fail('the rebuilt editor lost the text')
+await browser.close()
+console.log('mark-broken: fallback, told failures, no leftover holders, a mode rebuilds')