Two host-side halves of the same sweep.
**The cadence latch.** `cadence_degraded` — which makes the control task refuse
bitrate CLIMBS — was latched true for as long as the session was escalated
(adaptive capture depth or pipelined retrieve), independently of whether encode
was still missing deadlines. The client cannot tell that refusal apart from an
encoder's real ceiling: both arrive as a short `BitrateChanged`, and two
identical ones latch a cap. Escalation needs ~20 net behind-frames, which a
startup hitch supplies while the ABR is still in slow start at the 20 Mbps
default — so one transient pinned the whole session there, long after the
escalation had bought back the headroom it was for, and escaping cost +12.5 %
per 60 s. An escalated session is still judged strictly (ANY net behind-frame
keeps it flagged, where an unescalated one gets the full bucket), but being
escalated no longer flags it by itself: escalating exists so cadence CAN be
held, and once it is, refusing climbs refuses the thing that worked. The rule
moves into `encode_behind_cadence` so it is stateable and testable.
**The silent re-target.** `adopt_built_bitrate` publishes the rate a rebuilt
pipeline actually opened at — `build_pipeline` re-resolves an Automatic rate
whenever the source delivers a size the session did not negotiate, the
mirrored-panel case — and the encoder's own clamp can land below what the
control task already acked. Neither reached the client, whose controller keeps
its own copy of that number as its climb base. A 1080p client mirroring a 4K
panel therefore believed 20 Mbps while the host encoded 60, and its first climb
computed from the stale base asked for 40: a re-target DOWNWARD, paying an
encoder rebuild to get there. Both paths now push the applied rate to the
control task, which sends `BitrateChanged` — the existing 9-byte message, which
already means precisely this and which clients already handle arriving
unprompted. No wire-format change, no capability negotiation, old clients
unaffected.
2 host tests added.
enricobuehler
48565c4e9e