1.2.0

October 2026. Adds API; nothing is removed and no library changes, so
upgrading is a version bump. PlayerEngine gains a requirement with a
default, so a host's own conformance still compiles.

Added

• setHostInBackground(_:). A host calls it on every background and
  foreground transition, whether or not picture in picture or AirPlay still
  shows video. In the background, a decode session fault that a rebuild
  cannot fix suspends video until the host returns, instead of failing
  playback. Audio plays on and the return restarts the picture at the
  playhead. Reported as recovery: decodeSessionParked.
• PlaybackBufferState.networkBytesPerSecond and
  PlaybackCacheMetrics.networkBytesPerSecond: what the link delivers while
  a request is in flight, over about the last ten seconds of transfers.
  Compared with the title's bitrate, it separates a link too slow for the
  title from anything else. bufferState is republished when a stall
  begins, so the figure is current then.

Fixed

• A lost VideoToolbox session is rebuilt once per fault burst, not once per
  playback generation. A session the system took twice, minutes apart and
  with no seek between, used to be reported as .undecodable on the second
  loss, and a host would fall back to a transcode. Now only a rebuilt session
  that fails before decoding 48 pictures is a verdict.