The app stays quick while helper sessions are working
Helpers no longer make the whole app wait on each other: their updates and the efficiency notes are written without stopping everything else.
While helper sessions worked in the background, every word they produced made the whole app pause for a moment, and one slow screen could hold up everything, including your own chat. The app now finishes the bookkeeping for a helper's update first and sends it to the window afterwards, in the same order as before, so nothing waits on it.
The efficiency notes had a similar habit: each step was saved to disk several times over, once for the session and once for every session above it, and each save waited for the disk to confirm. Those notes are now written straight away and confirmed together in one go, after the app has moved on. Budget limits are still confirmed immediately, so a spending cap is never at risk.