ReplayPacer (MsgListener+MsgTalker) sits between packetizer output and
downstream listeners; sleeps after each complete NMEA/UBX frame before
forwarding. FileBackend no longer owns the delay — it reads as fast as
possible and the pacer provides back-pressure on the same thread.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
