macltok

account: fetch backed-up room keys only when a decryption fails

OneShot downloads the whole backup in one response the moment a verification or a recovery hands over its key, then decrypts every key in a loop that never yields, which on the wasm worker's single thread stalls every timeline until it ends. That fits malice's report of all rooms dying after SAS until a reload. The sdk's own comment says it doesn't work for any sizeable account.