on_media admitted a packet whenever its generation matched the one the
session was built for. A restarted zmc starts again at generation 0, so
if the camera came back with different parameters its replayed keyframe
passed that check and went into the old codec's packer before the main
thread rebuilt the session.
Move the HELLO and generation bookkeeping into RtspSessionTracker, a
small class with no locking or RTSP types. Every HELLO and every
disconnect clears the confirmed flag; Update() asks the tracker for a
plan (none, adopt, rebuild), acts on it and confirms; on_media feeds the
packers only for a confirmed session at the confirmed generation. A set
that failed to build (unsupported codec) is not retried until a new
HELLO arrives, so a bad camera does not rebuild on every pass.
Tests: a new suite for the tracker covers the complete-set rule, the
HELLO-to-rebuild window, generation reuse after a producer restart with
changed and with unchanged parameters, audio appearing, disappearing and
changing, a generation without video, a failed build, and HELLOs for
streams the server does not serve.
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
