feat(admin): reload once when a chunk fails to load after a deploy (quick-261028-rqb)

- installChunkReloadGuard reloads on vite:preloadError, at most once per
  60 s through a sessionStorage timestamp; no storage means no reload

admin/src/app/chunkReload.ts

@@ -0,0 +1,63 @@
+// Reload once when a chunk fails to load. After a deploy, an old tab that
+// asks for a hashed chunk the new build removed fails the dynamic import, and
+// Vite's preload helper dispatches vite:preloadError on window. One reload
+// loads the new index and its chunks. A timestamp in sessionStorage stops a
+// reload loop when the reload does not help, and without usable storage the
+// guard never reloads. It does not call preventDefault: the error still
+// reaches the importer (RichEditorField switches to source mode), so when the
+// guard declines, the existing failure state shows.
+
+export const CHUNK_RELOAD_KEY = 'summer-admin.chunk-reload'
+/** No second automatic reload within 60 seconds of the last one. */
+export const CHUNK_RELOAD_WINDOW = 60_000
+
+/**
+ * Whether the guard may reload now. It records now under CHUNK_RELOAD_KEY
+ * when it says yes. Null storage, a reload within CHUNK_RELOAD_WINDOW or
+ * storage that throws means no.
+ */
+export function shouldReload(storage: Storage | null, now: number): boolean {
+  if (storage === null) {
+    return false
+  }
+  try {
+    const last = Number.parseInt(storage.getItem(CHUNK_RELOAD_KEY) ?? '', 10)
+    if (Number.isFinite(last) && now - last >= 0 && now - last < CHUNK_RELOAD_WINDOW) {
+      return false
+    }
+    storage.setItem(CHUNK_RELOAD_KEY, String(now))
+    return true
+  } catch {
+    return false
+  }
+}
+
+function sessionStore(): Storage | null {
+  try {
+    return window.sessionStorage
+  } catch {
+    return null
+  }
+}
+
+export interface ChunkReloadOptions {
+  target?: Pick<EventTarget, 'addEventListener' | 'removeEventListener'>
+  storage?: () => Storage | null
+  reload?: () => void
+  now?: () => number
+}
+
+/** Installs the vite:preloadError guard and returns its uninstall function. */
+export function installChunkReloadGuard(options: ChunkReloadOptions = {}): () => void {
+  const target = options.target ?? window
+  const storage = options.storage ?? sessionStore
+  const reload = options.reload ?? (() => window.location.reload())
+  const now = options.now ?? Date.now
+  const listener = (): void => {
+    if (shouldReload(storage(), now())) {
+      reload()
+    }
+  }
+  target.addEventListener('vite:preloadError', listener)
+  return () => target.removeEventListener('vite:preloadError', listener)
+}