Phase 8 decision: no vJoy — XP gets RioGamepadXP.sys, our own HID minidriver

vJoy/PPJoy are unmaintained, so third-party virtual joysticks are out.
The XP joystick becomes a thin WDM HID minidriver (vhidmini shape,
WDK 7.1.0, x86, no signing required on XP) exposing the same Public.h
IOCTL + 25-byte report contract as the modern RioGamepad.sys, so
HidFeederJoystickSink drives both. Precedent: FASA's tasgame.sys was an
XP HID minidriver. Staged: XP app ships keyboard/lamps/plasma first,
driver as milestone 2. Win10/11 chain unchanged (ViGEm preferred).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/PLAN.md

@@ -304,7 +304,7 @@ lamps, plasma, wallpaper apply).
 | | Windows 10/11 (unchanged) | Windows XP SP3 |
 |---|---|---|
 | TFM / arch | net48, x64 | **net40, x86** (.NET 4.0 is XP's ceiling; 4.5+ needs Vista) |
-| Virtual joystick | ViGEm → RioGamepad → vJoy → none | **vJoy 2.0.x** (last XP driver line) — full 6-axis/96-button fidelity |
+| Virtual joystick | ViGEm → RioGamepad → none (unchanged) | **RioGamepadXP.sys** — our own thin WDM HID minidriver (same feeder contract) — full 6-axis/96-button fidelity |
 | Overlay render | SkiaSharp (generate + apply) | consume pre-rendered wallpaper only (**PNG→BMP** — XP's `SystemParametersInfo` takes BMP only) |
 | Editor | full (incl. wallpaper maker) | mapping editor only (pure WinForms/GDI+); wallpaper maker gated (Skia) |
 | JSON | System.Text.Json → **Newtonsoft 13** | Newtonsoft 13 (STJ needs net461+; one serializer for both flavors) |
@@ -321,13 +321,26 @@ lamps, plasma, wallpaper apply).
   (`ViGEmJoystickSink`, `HidFeederJoystickSink`, `Hid/`).
   *Risk fallback:* if Bcl.Async misbehaves on real XP, the receive loop
   reverts to a dedicated thread (the legacy `CommWatchProc` shape) for net40.
-- **8B — vJoy sink (both flavors):** `VJoyJoystickSink : IJoystickSink`
-  P/Invoking `vJoyInterface.dll` (SDK already on hand in docs/vJoy_SDK/);
-  arch-matched DLL load; report packing pure + unit-tested. Acquisition
-  order (decided): **the Xbox 360 pad (ViGEm) stays preferred on 10/11** —
-  net48: ViGEm → RioGamepad → vJoy → Null (vJoy is fallback only);
-  net40: vJoy → Null (the XP primary). Pin installers:
-  2.0.5 (XP) / 2.1.9.1 (signed, 10/11) in `deploy/vendor/`.
+- **8B — RioGamepadXP.sys, the XP flavor of our own driver.** Third-party
+  virtual-joystick drivers are ruled out (decided: **no vJoy** — the project
+  is unmaintained; PPJoy likewise). Instead, rebuild the thin driver side of
+  our existing split for XP: a **WDM HID minidriver** in the shape of the
+  DDK `vhidmini` sample (`HidRegisterMinidriver`, x86), exposing the **same
+  `Public.h` contract** as the modern driver — identical
+  `IOCTL_RIO_SUBMIT_REPORT`, identical 25-byte report, same descriptor
+  (6×16-bit axes, hat, 96 buttons) — so the existing `HidFeederJoystickSink`
+  drives it unchanged (only the device path differs). Precedent: the
+  original FASA `tasgame.sys` was exactly an XP HID minidriver
+  (docs/Win32RIO/, analyzed); ours stays thin with serial in user mode.
+  Toolchain: **WDK 7.1.0** (last XP-capable kit) under `driver/RioGamepadXP/`;
+  XP x86 enforces no kernel signing, so install is just the INF — none of
+  the Phase 1 test-signing/Secure Boot friction exists there.
+  Acquisition order (decided): **the Xbox 360 pad (ViGEm) stays preferred
+  on 10/11** — net48: ViGEm → RioGamepad → Null (unchanged);
+  net40: RioGamepadXP → Null.
+  *Staging:* the XP app is useful before the driver lands — milestone 1
+  ships keyboard/mouse + lamps + plasma (joystick = Null sink), the driver
+  follows as milestone 2.
 - **8C — Tray on net40/x86:** multi-target `RioJoy.Tray` (net40 drops the
   ViGEm + RioJoy.Overlay references); gate `WallpaperMakerForm` + overlay
   generation; `WallpaperApplier` converts PNG→BMP via GDI+ before
@@ -336,21 +349,23 @@ lamps, plasma, wallpaper apply).
   pre-rendered on a modern machine (`RioProfile.WallpaperPath` travels with
   the config).
 - **8D — Packaging:** `build-package.ps1 -Flavor XP` →
-  `RIOJoy-XP-<ver>.zip` (net40/x86 publish, vJoy 2.0.5 installer,
+  `RIOJoy-XP-<ver>.zip` (net40/x86 publish, RioGamepadXP.sys + INF,
   `.bat` install/uninstall, README-DEPLOY-XP: prereqs XP SP3 + .NET 4.0 Full
   + KB2468871). Modern zip unchanged; release both to Gitea.
 - **8E — Verification:** full suite stays net48-hosted (xUnit needs
   net452+; shared sources are what's tested) + a tiny net40 console
   self-test for the shims, run on XP. Ladder: net40/x86 binary boots on
-  Win10 → XP VM with vRIO over a virtual COM pair → real cabinet
-  (joy.cpl shows 6 axes + 96 buttons, SendInput into a game, lamps,
-  plasma, auto-switch yield, BMP wallpaper).
+  Win10 → XP VM with vRIO over a virtual COM pair (app milestone; the
+  driver needs real/virtualized XP too — vhidmini-class drivers run fine
+  in a VM) → real cabinet (joy.cpl shows 6 axes + 96 buttons, SendInput
+  into a game, lamps, plasma, auto-switch yield, BMP wallpaper).
 - **To confirm before starting:** (1) keep the mapping editor on XP or ship
   runtime-only? (2) which XP cabinets / how do files get onto them (drives
   the .bat installer shape)?
   *Decided:* the Xbox 360 pad (ViGEm) remains the preferred controller on
-  Windows 10/11 whenever ViGEmBus is present; vJoy is only the fallback
-  there, and the primary on XP.
+  Windows 10/11 whenever ViGEmBus is present. **No third-party virtual
+  joystick drivers** (vJoy/PPJoy are unmaintained) — XP gets our own
+  RioGamepadXP.sys instead.
 
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