- C-3: Socks5ProducerBuilder.bind_policy(bool) — the substrate-free
entry's explicit BIND gate, defaulting to the accept seam's
presence; seam presence is never the sole gate
- D-2: RegisterMode::ProducerBuilder + an integration test wiring the
full builder through .register(...) serving all three commands
- S-1: run_datagram_stage's doc names the hot-Ok(None) residual
- N-2: wire.md §UDP ASSOCIATE carries the inline-send backpressure line
Verified: cargo test (352 green), clippy/fmt/doc clean, wasm checks clean.