Three related gaps closed so one full byse account stops wasting
attempts on every subsequent job and later-added accounts get picked
up without an app restart.
1. Pre-job-swap moved BEHIND the semaphore acquire. At scale (500 jobs
/ 1 slot) every worker was checking _failedAccounts at spawn time
before the first upload had even tried — so none of them saw the
failed state. Now each worker re-checks right before its first
upload attempt.
2. save-config IPC handler re-resolves fallbacks for any account that
is already in _failedAccounts but has no override set. Previously
account-failed only fired once per account, so a config change
after the first mark-failed was silently ignored and the batch
stayed stuck on the dead account until the app restarted.
3. UploadManager exposes getFailedAccountKeys() and getOverride(hoster)
so main.js can drive the late re-resolve without poking private
fields.
4 new tests: pre-job-swap after semaphore, getters contract, fresh
manager resets learned state, late-added fallback is honored by
subsequent jobs. 80/80 green.
bf806cb069