ethernet-gateway v0.5.4

Added

Serial Console Mode

• Telnet-serial bridge as a second role for the serial port,
  alongside the existing Hayes AT modem emulator. Selectable via the
  new serial_mode config key (modem / console). The existing
  G Serial Gateway main-menu item now bridges the telnet/SSH session
  straight to the wire so an operator can drive a microcontroller,
  RS-232 device, or other serial console remotely.
• Hot mode switch — flipping serial_mode (from the GUI dropdown,
  the new T Toggle Modem/Console mode entry on the Configuration
  menu, or egateway.conf directly) reconfigures the running serial
  thread within one manager-poll interval. No restart required.

Changed

• Configuration menu reorganized to surface the new mode toggle and
  to relabel M Modem Emulator ↔ M Serial Console based on
  current serial_mode. The new menu walkthrough is documented in
  user-manual §5.6.
• Documentation pass: §3.2 of the user manual gained 22 previously
  undocumented config keys (the full kermit_* family,
  ssh_gateway_auth, disable_ip_safety, allow_atdt_kermit,
  kermit_server_enabled / _port); index.html grew a Kermit
  subsection in the file-transfer config tables and added cross-links
  to kermit.html from each protocol-prompt step; the chapter-8 intro
  now correctly describes five protocols (the old "three related
  protocols" framing predated the ZMODEM and Kermit chapters).

Fixed

Console bridge hardening

• run_console_bridge could wedge indefinitely when the telnet
  peer's TCP write buffer was full: the spawned async task's
  duplex_write.write_all().await would park with no wake-up source,
  stranding the manager thread until process restart. Bounded with a
  200 ms timeout then abort().
• Orphaned bridge requests on serial-mode flip: a request that
  arrived in the slot just before SERIAL_RESTART fired could be
  silently abandoned because console_manager_tick returned without
  polling the slot, leaving the requester's rx.await blocked forever.
  Slot is now drained with Err("Serial mode changed") on every exit
  path.
• TOCTOU between request-eligibility check and slot insert:
  request_console_bridge now re-checks
  check_console_bridge_eligible under the slot lock so an operator
  flipping serial_mode (or disabling serial, or clearing the port
  path) and calling restart_serial() in the narrow window between
  the fast-path check and the slot insert can no longer leave a
  request stuck until shutdown.
• Unbounded session_to_port channel replaced with a bounded
  tokio::sync::mpsc::channel(64); a flow-controlled wire (CTS-low,
  slow peer) plus a fast typist or paste can no longer balloon
  in-memory queue depth. The async-side .send().await now
  backpressures duplex_read, which backpressures the telnet peer.
• Slot-cleanup duplication removed from the Err(_) arm of
  rx.await; let ConsoleSlotGuard's drop own slot teardown.

Serial mode switch responsiveness

• Modem online loops (online_mode_tcp, online_mode_duplex) now
  honor SERIAL_RESTART on every iteration; previously a mode flip
  could lag by one block-read interval before the loop noticed.

Menu UX & doc-vs-code drift

• G Serial Gateway and T Toggle Modem/Console mode are
  now hidden from sessions that arrived over the serial port itself.
  The handler-side rejections remain as defense in depth (a serial-side
  caller can still type the letter blind), but the menu no longer
  advertises items that always error.
• Manual cross-references to "chapter 9.10" corrected to "9.13"
  (Console Mode lives at 9.13; 9.10 is Chained Command Lines).
• AT&K1 redescribed as Auto-detect (stored, no wire effect)
  instead of "Reserved"; the parser at src/serial.rs:1140 accepts
  &K1 and emits FlowSet(1). Missing &K1 row added to Appendix
  B.4.
• AT&F entry now notes that it drops the active connection,
  matching the AtResult::Reset return.
• Bare kermit alias for ATDT KERMIT documented alongside the
  existing kermit-server / kermit server aliases.