Write design/steam-deck-passthrough-plan.md — the build plan to ship exact Steam
Deck pass-through from the Linux client (incl. the Steam + QAM buttons) plus a
virtual Deck on any Linux host. Key validated facts captured so the next session
doesn't re-investigate:
- Client capture is ALREADY correct: SDL3 maps Steam->Guide, QAM->Misc1; the
client forwards BTN_GUIDE/BTN_MISC1; the host maps them to btn::STEAM/btn::QAM.
Only precondition: Steam Input disabled on the client (the Decky UX).
- Shippable host transport = usbip + vhci_hcd (in-tree + signed everywhere, no
module build, no MOK) — PROVEN on Bazzite: Steam promotes the usbip interface-2
Deck (XInput slot + X-Box pad), identical to raw_gadget on SteamOS.
- Build steps: refactor steam_gadget.rs into shared Deck-logic + a transport
trait; add the usbip transport (vendor-trim the usbip crate to drop rusb/libusb,
in-process vhci attach); transport-select raw_gadget->usbip->UHID/DualSense;
client leave-shortcut (controller chord + Ctrl+Alt+Shift+D); serial polish.
Also checks in the working usbip Deck PoC (packaging/linux/steam-deck-gadget/
usbip-poc/) for the next session to build on. Not pushed.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
