KAI-728 · chunked delivery, locked screen, installed PWA
Just in time holds only 10 to 30 s of audio ahead of the playhead, so a chunk has to be fetched and appended roughly every 20 s, including while the screen is locked. That is the case that breaks, and it means playback can coast at most about 30 s if chunk delivery dies. Buffer all up front is the control: if that survives a lock and just in time does not, the problem is chunk arrival, not playback.
Newest first. Persisted to this device on every entry, so it survives the page being frozen or discarded while backgrounded.