AetherEngine 5.18.6

Fixed

Remote HLS external WebVTT subtitles now recover when the legible media selection loads after the item is ready.

On the nativeRemoteHLS bypass the engine surfaces the item's legible AVMediaSelectionGroup as subtitleTracks. The discovery loaded that group exactly once, and if loadMediaSelectionGroup(for: .legible) returned an empty group at that instant it gave up for the whole session, leaving subtitleTracks permanently empty.

On macOS 26 the group is populated once the master playlist is parsed (before readyToPlay), so the single load caught every rendition. A reporter on macOS 27 beta saw a permanently empty subtitle picker, because on that OS the legible group only fills once the item reaches readyToPlay, and the one-shot load missed it.

The discovery now retries the group load once after readyToPlay before giving up, so a late-populating legible group no longer drops the renditions. The fast path is unchanged: a non-empty first load skips the wait.

Reported by jihongboo (#154).

Full Changelog: 5.18.5...5.18.6