novel-bookmark.user.js was split out of manga-bookmark.user.js and lost
four constants: CACHE_KEY, LASTCHECKED_KEY, LATEST_CHECK_THROTTLE_MS and
LATEST_CHECK_BATCH. Every use sits behind a try/catch or a
fire-and-forget promise, so the ReferenceErrors were swallowed:
backgroundRefreshLatest() threw before its first fetch, and the local
cache silently read empty and never persisted.
The issue named the two throttle constants; the cache keys are the same
lost lines and are fixed here too.
Add a static guard over both scripts, since no behavioural test can see
a swallowed ReferenceError.
sulthan