fix(console): switch conman from ser2net-telnet to direct serial access

The ser2net layer between conman and the serial devices was causing
stair-stepping in terminal output. conman's dev="host:port" uses telnet
protocol, but ser2net's accepter was raw TCP (no telnet mode). The telnet
NVT state machine in conman was stripping bare CR characters from device
output — particularly from Dell switches that use old-style \n\r (LF+CR)
line endings instead of standard \r\n. In telnet, a bare \r not followed
by \n or NUL is non-compliant and gets dropped, leaving bare \n that
causes stair-stepping in the raw-mode terminal.

Fix: conman now opens serial devices directly via the stable udev
symlinks (/dev/consoles/<name>) with seropts, eliminating the telnet
layer entirely. ser2net is stopped and disabled but remains installed
for emergency TCP access (documented workflow: stop conmand, start
ser2net, use telnet, then reverse).

Architecture change:
  Before: device → serial → ser2net (raw TCP) → conman (telnet NVT) → terminal
  After:  device → serial → conman (direct) → terminal

Verified: 7/7 serial devices held by conmand, 7/7 log files capturing,
all \r bytes preserved in terminal output (confirmed via PTY capture).

💘 Generated with Crush

Assisted-by: Crush:glm-5.2

console/README.md

@@ -6,17 +6,18 @@ switches and routers, running on **pfv-tsys4** (storage server).
 ## Architecture
 
 ```
-USB-DB9 adapters → udev symlinks (/dev/consoles/<name>) → ser2net (TCP) → conman (logging + multiplexing)
+USB-DB9 adapters → udev symlinks (/dev/consoles/<name>) → conman (direct serial, logging + multiplexing)
 ```
 
-ser2net owns the physical serial devices and exposes them on TCP ports
-bound to the **Tailscale interface only** (`100.70.77.93:200X`). conman
-connects to those TCP ports for session logging, output capture, and
-multi-user console sharing.
+conman opens the serial devices directly via stable udev symlinks and
+provides session logging, output capture, and multi-user console
+sharing. Clients connect to conmand over the Tailscale interface
+(`100.70.77.93:7890`).
 
-**conman and ser2net do NOT share ports** — only one process can open a
-serial device at a time. ser2net owns the physical device; conman connects
-over TCP.
+ser2net is installed but **disabled** — kept for emergency direct TCP
+access only (see [Emergency Access](#emergency-access) below). It must
+NOT run simultaneously with conmand (both would compete for the serial
+devices).
 
 ## The USB Enumeration Problem (SOLVED)
 
@@ -49,7 +50,8 @@ ID_PATH. On subsequent boots, udev creates them automatically.
 | 2006 | subodev-torsw | usb-0:1.5.4.1 | Suborbital device TOR switch |
 | 2007 | pfv-r2-sw | usb-0:1.6.3.2 | Rack 2 old Dell switch |
 
-All ports listen on the Tailscale IP (`100.70.77.93`).
+TCP ports are used by the ser2net emergency config only. conman accesses
+serial devices directly via `/dev/consoles/<name>` symlinks.
 
 ## Scripts
 
@@ -74,19 +76,24 @@ conman -d pfv-tsys4:7890 -q                    # list all consoles
 
 Escape sequence: `&.` to disconnect, `&?` for help.
 
-**Direct telnet (emergency only — conflicts with conman):**
+### Emergency Access
+
+If conmand is down or you need direct serial access:
 
 ```bash
-# Direct telnet to ser2net works ONLY when conmand is stopped, because
-# conmand maintains persistent connections to all 7 TCP ports. Use:
+# Option A — direct screen on pfv-tsys4:
 ssh pfv-tsys4 'systemctl stop conmand'
+ssh pfv-tsys4 'screen /dev/consoles/pfv-core-sw01'
+ssh pfv-tsys4 'systemctl start conmand'
+
+# Option B — enable ser2net for TCP access:
+ssh pfv-tsys4 'systemctl stop conmand && systemctl start ser2net'
 telnet pfv-tsys4 2001                          # pfv-core-sw01
-ssh pfv-tsys4 'systemctl start conmand'        # restart when done
+ssh pfv-tsys4 'systemctl stop ser2net && systemctl start conmand'
 ```
 
-**Do NOT use telnet while conmand is running** — conmand will reconnect
-and kick your telnet session immediately ("Connection closed by foreign host").
-The correct workflow is conman client → conmand → ser2net → device.
+**Never run ser2net and conmand at the same time** — both compete for the
+same serial devices.
 
 ### Re-deploy after changing mapping.txt
 
@@ -108,7 +115,7 @@ to `mapping.txt`.
 | File | Purpose |
 |------|---------|
 | `/etc/udev/rules.d/99-console-ports.rules` | Stable symlinks by ID_PATH |
-| `/etc/ser2net.yaml` | ser2net config (TCP ports → serial symlinks) |
+| `/etc/ser2net.yaml` | ser2net config (EMERGENCY ONLY — disabled by default) |
 | `/etc/conman.conf` | conman config (CONSOLE entries between markers) |
 | `/etc/systemd/system/conmand.service` | systemd unit for conmand |
 | `/root/console/mapping.txt` | Copy of the source-of-truth mapping |