SubtitleCueHistory

Every cue the session produced, for its whole lifetime. A late handler starts complete and a re-demuxed region is never delivered twice. Memory grows with the text the title carries — fine for a film, not necessarily for a long captioned stream or a disc with many tracks.

The newest cues only, at most maxCues of them and at most maxBytes of UTF-8 between their text and their dedup keys (a key is the cue's stream, source times and text, so a cue costs a little over twice its text). The oldest go first, cue and key together.

What a host opting in takes on:

• A replay is the retained window, not the film: a late handler, or a re-registration after setSubtitleDelaySeconds, sees only what is still held (with the delay in force now, as under .complete).
• Dedup covers the retained window only. A seek far enough back that the region's cues were evicted re-demuxes them, and they are delivered again.
• A single cue larger than maxBytes is delivered live and never retained (keeping it would mean evicting everything else for one cue that still would not fit). It is counted in evictedCues.
• Cues produced before the presentation origin is known wait in a queue bounded the same way; what overflows it was never delivered and is counted in droppedBeforeOrigin.

Both limits are clamped to at least 1 when the session is built, so Options.subtitleCueHistory reads back the bound in force. A maxBytes of 1 is a valid "no history": every cue is live-only.