WSL2: replug must auto-recover — CYD should resume exactly as before without manual steps #10

Problem

Under WSL2, physically unplugging and replugging the CYD breaks the hub and it does not recover on its own — the display falls back to hub offline and stays there until the user manually intervenes.

Observed chain on replug:

1. The usbipd-win attachment is lost → /dev/ttyUSB0 disappears from WSL.
2. serial_bridge is left polling a dead port (/dev/ttyUSB0 unavailable; retrying...).
3. On replug, even after re-attaching, the new device node comes back as root:dialout — so without dialout membership it's permission-denied again.
4. Net result: firmware shows hub offline; user must manually re-attach + restart serial_bridge.

Desired behavior: plug the CYD back in → within a few seconds the session list is back exactly as before, zero manual steps.

Solution proposals

Three pieces are needed; each addresses one link in the chain.

1. Auto re-attach the USB device (Windows/usbipd side)

usbipd can keep re-attaching across replugs:

usbipd.exe attach --wsl --hardware-id 1a86:7523 --auto-attach

This is a long-running foreground process that re-attaches the device the moment it reappears, so /dev/ttyUSB0 comes back automatically. Run it as a supervised background process (see #3).

2. Stable, permission-correct device node (WSL side)

• Add the user to dialout once (sudo usermod -aG dialout $USER) so the freshly-created node is accessible without chmod after every replug (see docs: list Linux prerequisites (build-essential, pkg-config, libudev-dev, dialout group) #8).
• Optional: a udev rule to pin a stable symlink + group, e.g.

  SUBSYSTEM=="tty", ATTRS{idVendor}=="1a86", ATTRS{idProduct}=="7523", SYMLINK+="cyd", GROUP="dialout", MODE="0660"
  

  and point serial_bridge at /dev/cyd so it's independent of ttyUSB0/ttyUSB1 numbering.

3. Self-healing bring-up (supervisor)

• Verify/strengthen serial_bridge's auto-reconnect so it survives the node disappearing and reappearing (README claims it reconnects on unplug/replug — confirm it doesn't exit on a vanished port).
• Provide a supervised setup so all three survive crashes and reboots. Options:
  • systemd user services (WSL has systemd): usbipd-attach.service (runs the --auto-attach), vibe-bridge.service, serial-bridge.service with Restart=always.
  • Or extend scripts/wsl-cyd-up.sh (feature: one-command WSL2 bring-up helper script (attach + bridge + serial_bridge) #9) to launch --auto-attach in the background and run serial_bridge in a while restart loop.

Acceptance criteria

• Unplug + replug the CYD → session list returns automatically within ~10 s, no commands run.
• Survives ttyUSB renumbering (ttyUSB0 → ttyUSB1).
• No chmod needed after replug.
• Documented in the WSL2 section (WSL2 support (umbrella): usbipd-win passthrough — bridge in WSL, COM ports invisible #4).

Related

• WSL2 support (umbrella): usbipd-win passthrough — bridge in WSL, COM ports invisible #4 (WSL2 umbrella), docs: list Linux prerequisites (build-essential, pkg-config, libudev-dev, dialout group) #8 (dialout/prereqs), feature: one-command WSL2 bring-up helper script (attach + bridge + serial_bridge) #9 (bring-up helper script)

Environment

Windows 11 + WSL2, CYD USB-SERIAL CH340 (1a86:7523).