feat: add CachyOS image (Gamescope + Steam)

- Add distros/cachyos image.yaml and helper files under files/
- Wire kernel packaging and --distro cachyos in build_image.sh
- Stage CachyOS artifacts in image-builder entrypoints; include cachyos in multi image
- Add boot/kexec-cachyos.sh and document in README

Co-authored-by: Cursor <cursoragent@cursor.com>

distros/cachyos/files/ps5-tty-session.sh

@@ -0,0 +1,73 @@
+# /etc/profile.d/ps5-tty-session.sh — tty1 autologin: Gamescope or Plasma (no SDDM).
+# Sourced from /etc/profile (login shells) and from ~/.bashrc (agetty autologin
+# usually starts a non-login shell). Idempotent guard avoids double-exec.
+
+case ${PS5_TTY_SESSION_INIT-} in
+1) return ;;
+esac
+PS5_TTY_SESSION_INIT=1
+export PS5_TTY_SESSION_INIT
+
+tty_path=$(tty 2>/dev/null) || tty_path=""
+[ "$tty_path" = "/dev/tty1" ] || return 0
+[ -z "${WAYLAND_DISPLAY-}" ] || return 0
+[ -z "${DISPLAY-}" ] || return 0
+
+SESSION_FILE="${XDG_CONFIG_HOME:-$HOME/.config}/ps5-next-session"
+mkdir -p "$(dirname "$SESSION_FILE")"
+[ -f "$SESSION_FILE" ] || echo gamescope >"$SESSION_FILE"
+read -r SESSION <"$SESSION_FILE" 2>/dev/null || SESSION=gamescope
+SESSION=$(printf '%s' "$SESSION" | tr -d '\r\n\t ')
+
+export LIBSEAT_BACKEND=logind
+
+case "$SESSION" in
+  desktop|plasma|plasma-wayland|plasmax11)
+    # Do not `exec` Plasma: if startplasma-{wayland,x11} exits immediately the login
+    # shell ends, getty respawns in a tight loop, and start-limit-hit fires. Default
+    # is Plasma Wayland from VT (no SDDM greeter Xorg). The plasmax11 token is an
+    # explicit X11 escape hatch via startx + startplasma-x11.
+    LOG=/tmp/ps5-tty-session.log
+    # KDE helper: wraps Plasma in a session bus only when one is not already provided
+    # by systemd --user. Plain dbus-run-session would start an isolated bus and break
+    # org.freedesktop.systemd1 activation, PipeWire sockets, and xdg-desktop-portal.
+    PLASMA_DBUS_WRAP=""
+    [ -x /usr/lib/plasma-dbus-run-session-if-needed ] && PLASMA_DBUS_WRAP=/usr/lib/plasma-dbus-run-session-if-needed
+    _run_plasma_dbus() {
+      if [ -n "${PLASMA_DBUS_WRAP}" ]; then
+        "$PLASMA_DBUS_WRAP" "$@"
+      elif [ -n "${DBUS_SESSION_BUS_ADDRESS-}" ]; then
+        "$@"
+      else
+        dbus-run-session -- "$@"
+      fi
+    }
+    rv=0
+    case "$SESSION" in
+      plasmax11)
+        if [ -x /usr/bin/startx ] && [ -x /usr/bin/startplasma-x11 ]; then
+          _run_plasma_dbus startx /usr/bin/startplasma-x11 -- >>"$LOG" 2>&1 || rv=$?
+        else
+          echo "$(date) startx or startplasma-x11 missing — falling back to gamescope" >>"$LOG"
+        fi
+        ;;
+      *)
+        if [ -x /usr/bin/startplasma-wayland ]; then
+          _run_plasma_dbus /usr/bin/startplasma-wayland >>"$LOG" 2>&1 || rv=$?
+        else
+          echo "$(date) startplasma-wayland missing — falling back to gamescope" >>"$LOG"
+        fi
+        ;;
+    esac
+    [ "$rv" = 0 ] || echo "$(date) plasma session exited rv=$rv" >>"$LOG"
+    echo gamescope >"$SESSION_FILE"
+    unset PS5_TTY_SESSION_INIT
+    export WLR_LIBINPUT_NO_DEVICES=1
+    exec /usr/bin/gamescope-session-ps5
+    ;;
+  gamescope|*)
+    echo gamescope >"$SESSION_FILE"
+    export WLR_LIBINPUT_NO_DEVICES=1
+    exec /usr/bin/gamescope-session-ps5
+    ;;
+esac