Turn the scan from sequential TX-then-RX into two io.concurrent engines on
std.Io.Threaded, fixing the M4 bug where replies arriving during transmit were
dropped and the RX deadline (anchored at socket-open) expired before draining.
The main thread is the non-blocking Io.Queue consumer and dashboard renderer.
- rx: Receiver keyed off a shared tx_done atomic; new pure planDrain anchors the
drain window at TX-completion, not socket-open, killing the quiet-gap early exit
during a slow TX. Hard-cap safety backstop anchored at drain start.
- output (new): cache-line-padded atomic Stats, truecolor/256/none palette
(violet gradient, neon-green, muted-gray), in-place multi-line live dashboard,
Unicode results table, NDJSON to stdout with visuals on stderr, full
NO_COLOR/CLICOLOR_FORCE/COLORTERM/--color chain plus a narrow-terminal fallback.
- tx: wall-clock deadline so a stalled TX ring can no longer hang the scan.
- cli: banner recolored to the violet gradient and routed through the color chain.
- targets: add 192.88.99.0/24 (6to4 relay anycast) to the RFC 6890 exclude floor.
78/78 unit tests pass under Debug and ReleaseSafe; proven end-to-end (open/closed,
dedup, dashboard, NDJSON) in an unshare -r -n netns under ReleaseSafe.
16429c20c2