nx_sfu_select.nx

nx_sfu_select.nx -- SOVEREIGN SELECTIVE-FORWARDING core (the jitsi-videobridge value prop, measured our #1 SOTA hole: relay had broadcast=7/selective=0 -> every receiver got every full-rate stream -> multi- party collapse). PURE LOGIC, no sockets: the relay integrates it thinly; this organ is gate-proven alone. MODEL (layers = geometries): a sender may mark each 0x57 frame HI (flags bit1=0, today's clients) or LO (bit1=1, e.g. 160x120 simulcast). Per (sender,receiver) pair the relay forwards EXACTLY ONE layer. A layer SWITCH happens only AT A KEYFRAME of the target layer -- to a geometry-flex receiver the switch is just a legal geometry change at a key: ZERO new client decode logic. The forwarded subset gets its seq REWRITTEN (out_seq++ per forwarded frame, the JVB trick) so dedupe+P-chain rules hold. SAFE BY CONSTRUCTION: default want=HI = exactly today's behavior; want=LO with a sender that never produces LO keeps HI flowing (no starvation); unknown flag bits ignored; senders/receivers cap 64. license_tier: ORIGINAL