Documents the previously-undocumented UDP gateway prior art discussed
with the alknet-channels POC agent (/workspace/tun2proxy/src/udpgw.rs):
per-datagram length framing over a stream (LEN|FLAGS|CONN_ID|[SOCKS5
addr]|DATA), SOCKS5 ATYP addressing in-band, CONN_ID flow multiplexing,
keepalive/ERR flag packets, MTU cap, idle expiry. Folds implications
into OQ-TN-01 (addressing fork: per-channel vs per-datagram), OQ-TN-02
(framing mechanics production-proven; remaining fork documented),
OQ-TN-07 (single-ALPN option strengthened), OQ-TN-09 (flag-packet
vocabulary maps to establishment/error frame question), OQ-TN-10 (UDP
POC scope narrowed to channels-layer fit), and the survey checklist.
Also records the transport story: TCP vs QUIC is the alkcall layer's
concern; the tunnel crate is transport-agnostic.
Captures the ten open design questions from the setup discussion:
addressing format, UDP datagram semantics, -L/-R/-D direction model,
no-forced-binding API surface, backend inversion point, two-pump
helper extraction, ALPN strategy, access control scope, lifecycle/
error reporting, and candidate targeted POCs. Includes the settled
foundation (POC-validated prior art), a prior-art survey list, and
the Phase 0 convergence checklist.