librtmp2 0.11.0

Added

• DeliveryHint (Critical / ResyncPoint / Droppable): the codec-neutral
  congestion class the relay already used per player, now public.
  RelayFrame::delivery_hint() classifies a frame from the existing init-cache
  classification, and Server::drain_exported_relay_frames_with_hints() returns
  each exported frame with its hint so a cluster relay can apply live-media
  backpressure without parsing codecs. drain_exported_relay_frames() is
  unchanged.
• examples/bench_relay prints an additional machine-readable delivered: line
  (aggregate Gbit/s and frames per viewer); existing output is unchanged.

Changed

• Fan-out sends no longer allocate per player and sendmsg: the iovec array
  lives on the stack (Transport::try_send_vectored takes the remaining parts
  plus an offset), and Conn::send_staged_media no longer builds a window
  Vec per call.
• StagedRelayMedia groups each player's messages while staging (a linked list
  per connection in one arena) instead of sorting all frames × players
  messages by connection after the fan-out; the send order per player is
  unchanged.

Tests

• Vectored-send tests on a socketpair (full and partial writes, resume at an
  offset, more than MAX_SEND_PARTS parts, EAGAIN, empty parts, closed
  peer), per-connection ordering of staged relay messages (staged and buffered
  players receive byte-identical streams), and DeliveryHint classification
  (H.264, E-RTMP, audio-only, script/metadata, malformed payloads).

Notes

• Measured with librtmp2-server's load benchmark (500–2000 viewers) the
  fan-out changes show no CPU regression and no gain beyond run-to-run noise:
  the cost is dominated by the kernel TCP path. See librtmp2-server's
  BENCHMARKS.md.
• Additive public API only (DeliveryHint, RelayFrame::delivery_hint,
  Server::drain_exported_relay_frames_with_hints); no FFI change.