fix(deploy): eGalax touchscreen on batm3 (kernel 6.6 + calibration)

The Dell 9030 AIO's built-in eGalax SAW panel (0eef:0001) was unusable:
touches either didn't register or landed in the wrong place. Full fix:

- Pin linuxPackages_6_6. On 25.11's default 6.12 kernel hid-multitouch
  grabs the controller and mis-parses its HID report (axes read stuck)
  and usbtouchscreen refuses to bind. On 6.6 usbtouchscreen binds and
  produces a clean single-touch ABS device (the known-good internal-SATA
  install runs 6.6.68). Mirrors douro.nix's per-hardware kernel pin.

- udev rule now modprobes usbtouchscreen ITSELF before unbinding usbhid
  and handing over via new_id. On a USB boot systemd-udev-trigger fires
  this rule (~2s) before systemd-modules-load loads usbtouchscreen
  (~12s), so new_id previously hit a not-yet-loaded driver and the panel
  bound to nothing. Loading it inline removes the boot-ordering race.

- Add an X evdev InputClass (99-egalax.conf) so X uses evdev + the
  transformation matrix rather than libinput. Mirrors the working
  internal-SATA install.

- egalax-calibrate: add XAUTHORITY (=/home/bitspire/.Xauthority) — the
  actual boot-time bug. Without the auth cookie xinput died with
  "Invalid MIT-MAGIC-COOKIE-1 key / Unable to connect to X server", so
  the coordinate-transformation matrix was never applied and touches
  landed in the wrong place. Also replace the fixed ExecStartPre sleep
  with a 30s retry loop on the eGalax X device appearing — more robust
  to boot timing than a race against display-manager.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

deploy/nixos/hardware/batm3.nix

@@ -12,6 +12,15 @@
       timeout = 3;
     };
 
+    # Pin the 6.6 LTS kernel. The Dell 9030 AIO's eGalax SAW touch panel
+    # (0eef:0001) works with the usbtouchscreen driver on 6.6 (the known-good
+    # internal-SATA install runs 6.6.68). On 25.11's default 6.12 kernel this
+    # old controller regressed: hid-multitouch grabs it and mis-parses the HID
+    # report ("failed to fetch feature 7", axes read stuck), usbtouchscreen
+    # refuses it, and touch is unusable regardless of udev/X config. Matching
+    # douro.nix's per-hardware kernel pin. Re-test touch before bumping this.
+    kernelPackages = pkgs.linuxPackages_6_6;
+
     initrd.availableKernelModules = [
       "xhci_pci"
       "ahci"
@@ -122,10 +131,20 @@
   '';
 
   # eGalax touchscreen (Dell 9030 AIO built-in panel)
-  # The eGalax HID descriptor confuses libinput (treats it as touchpad).
+  # By default usbhid/hid-multitouch claim the eGalax and mis-parse its
-  # Fix: unbind from usbhid at boot, bind to usbtouchscreen kernel module,
+  # HID report descriptor (X axis reads as stuck), so touch is unusable.
-  # then apply calibration matrix after X11 starts.
+  # Fix: hand the device to the usbtouchscreen kernel driver, which parses
-  # Unbind eGalax from usbhid, bind to usbtouchscreen
+  # the raw eGalax protocol into a clean single-touch ABS device that the
+  # X evdev driver + calibration matrix (below) map correctly. This mirrors
+  # the known-good internal-SATA install.
+  #
+  # The RUN command modprobes usbtouchscreen ITSELF before unbinding usbhid
+  # and handing over via new_id. usbtouchscreen is also in boot.kernelModules
+  # (systemd-modules-load), but on a USB boot systemd-udev-trigger fires this
+  # rule (~2s) BEFORE modules-load gets usbtouchscreen in (~12s) — so the
+  # new_id write hit a not-yet-loaded driver and the panel was left bound to
+  # nothing. Loading it inline here makes the handoff independent of that
+  # boot-ordering race (on internal-SATA boot the order happened to work).
   services.udev.extraRules = lib.mkAfter ''
     KERNEL=="ttyS[0-9]*", MODE="0666"
     KERNEL=="ttyUSB[0-9]*", MODE="0666"
@@ -133,7 +152,25 @@
     SUBSYSTEM=="tty", ATTRS{serial}=="DDDLb103Y23", SYMLINK+="ttyF56", MODE="0666"
     SUBSYSTEM=="tty", ATTRS{serial}=="A9YW78OC", SYMLINK+="ttyMEI", MODE="0666"
     SUBSYSTEM=="tty", ATTRS{serial}=="A9ZF8ELY", SYMLINK+="ttyNFC", MODE="0666"
-    ACTION=="add", SUBSYSTEM=="usb", ATTRS{idVendor}=="0eef", ATTRS{idProduct}=="0001", RUN+="${pkgs.bash}/bin/bash -c 'echo ''$kernel:1.0 > /sys/bus/usb/drivers/usbhid/unbind 2>/dev/null; echo 0eef 0001 > /sys/bus/usb/drivers/usbtouchscreen/new_id 2>/dev/null'"
+    ACTION=="add", SUBSYSTEM=="usb", ATTRS{idVendor}=="0eef", ATTRS{idProduct}=="0001", RUN+="${pkgs.bash}/bin/bash -c '${pkgs.kmod}/bin/modprobe usbtouchscreen 2>/dev/null; echo ''$kernel:1.0 > /sys/bus/usb/drivers/usbhid/unbind 2>/dev/null; echo 0eef 0001 > /sys/bus/usb/drivers/usbtouchscreen/new_id 2>/dev/null'"
+  '';
+
+  # Force the X evdev driver on the eGalax (not libinput). The usbtouchscreen
+  # node is a plain single-touch absolute device; evdev + the transformation
+  # matrix in egalax-calibrate below give correct orientation. Mirrors the
+  # working internal-SATA install's /etc/X11/xorg.conf.d/99-egalax.conf.
+  environment.etc."X11/xorg.conf.d/99-egalax.conf".text = ''
+    Section "InputClass"
+        Identifier "eGalax Touchscreen"
+        MatchVendor "0eef"
+        MatchProduct "0001"
+        MatchDevicePath "/dev/input/event*"
+        Driver "evdev"
+        Option "InvertY" "false"
+        Option "InvertX" "false"
+        Option "SwapAxes" "false"
+        Option "Calibration" ""
+    EndSection
   '';
 
   # Apply touchscreen calibration after X11 starts
@@ -147,9 +184,26 @@
       Type = "oneshot";
       RemainAfterExit = true;
       User = "bitspire";
-      Environment = "DISPLAY=:0";
+      # DISPLAY *and* XAUTHORITY — without the auth cookie xinput dies with
-      ExecStartPre = "${pkgs.coreutils}/bin/sleep 3";
+      # "Invalid MIT-MAGIC-COOKIE-1 key / Unable to connect to X server" and
-      ExecStart = "${pkgs.xorg.xinput}/bin/xinput set-prop 'eGalax Inc. USB TouchController' 'Coordinate Transformation Matrix' 0 -1.268 1.147 -1.224 0 1.118 0 0 1";
+      # the matrix is never applied, so touches register but land in the wrong
+      # place (the panel then feels dead). This was the actual boot-time bug.
+      Environment = [ "DISPLAY=:0" "XAUTHORITY=/home/bitspire/.Xauthority" ];
+      # Wait for the eGalax X device to appear (usbtouchscreen binds a little
+      # after display-manager on a USB boot) and retry, instead of a fixed
+      # sleep — more robust to boot timing. Matrix: swap X/Y + invert + scale
+      # to the active panel area (matches the known-good internal install).
+      ExecStart = pkgs.writeShellScript "egalax-calibrate" ''
+        for i in $(${pkgs.coreutils}/bin/seq 1 30); do
+          if ${pkgs.xorg.xinput}/bin/xinput list --name-only 2>/dev/null | ${pkgs.gnugrep}/bin/grep -qx 'eGalax Inc. USB TouchController'; then
+            exec ${pkgs.xorg.xinput}/bin/xinput set-prop 'eGalax Inc. USB TouchController' \
+              'Coordinate Transformation Matrix' 0 -1.268 1.147 -1.224 0 1.118 0 0 1
+          fi
+          ${pkgs.coreutils}/bin/sleep 1
+        done
+        echo "egalax-calibrate: eGalax device not found after 30s" >&2
+        exit 1
+      '';
     };
   };