updated docs

README.md

@@ -4,12 +4,18 @@
 
 Lineage: forked from [Super-Shift-S-Omarchy-Deck-Mode](https://git.no-signal.uk/nosignal/Super-Shift-S-Omarchy-Deck-Mode), briefly renamed Omarchy Deck, then renamed DeckShift.
 
-> **Target:** [Omarchy](https://omarchy.com) — Arch + Hyprland + SDDM + Walker. DeckShift depends on Omarchy-specific helpers (`omarchy-pkg-add`, `omarchy-restart-walker`, etc.) and is not intended to be cross-distro.
+> **Target:** [Omarchy](https://omarchy.com) — Arch + Hyprland + SDDM + Walker. Experimental DMS/greetd manual session switching is available through `DECKSHIFT_SESSION_BACKEND=dms-greeter-manual`. DeckShift still depends on Omarchy-specific helpers (`omarchy-pkg-add`, `omarchy-restart-walker`, etc.) and is not intended to be cross-distro.
 
 [![DeckShift demo](https://img.youtube.com/vi/nj4pLh3spCs/maxresdefault.jpg)](https://youtu.be/nj4pLh3spCs)
 
 ## What's New
 
+### Unreleased — Session backend abstraction
+
+- DeckShift now writes `/etc/deckshift/session-backend.conf` and routes mode selection through `/usr/local/bin/deckshift-session-switch` plus `/usr/local/bin/deckshift-session-transition`.
+- `sddm` preserves the existing behavior: update `/etc/sddm.conf.d/zz-gaming-session.conf`, then restart SDDM.
+- `dms-greeter-manual` is experimental: it writes DMS greeter memory to select the target session, then terminates the current login session so the user authenticates through DMS. It does not implement one-shot auto-login yet.
+
 ### v0.1.13 — Pacman hook keeps gamescope's cap_sys_nice across upgrades
 
 - Linux file capabilities live as an xattr (`security.capability`) on the inode, so every time pacman replaces `/usr/bin/gamescope` during an upgrade the previously-granted `cap_sys_nice=eip` is silently lost. Performance mode keeps "working" but the compositor thread loses its priority boost — worse frame pacing and input latency, with no error surfaced anywhere.
@@ -117,11 +123,11 @@ This installer transforms your desktop into a dual-mode system:
 - **Desktop Mode** — your normal Hyprland session.
 - **Gaming Mode** — full-screen Steam Big Picture running inside Gamescope (the same compositor used by the Steam Deck), with automatic performance tuning, controller support, and external drive mounting.
 
-Switching between modes is seamless — SDDM handles session transitions, and your network, audio, and peripherals carry over automatically.
+Switching between modes is handled by a session backend. SDDM remains the default and preserves the seamless auto-login flow. The experimental DMS greeter backend preselects the next session and returns to the greeter for manual authentication.
 
 ## Requirements
 
-- **OS**: [Omarchy](https://omarchy.com) (Arch Linux + Hyprland + SDDM)
+- **OS**: [Omarchy](https://omarchy.com) (Arch Linux + Hyprland + SDDM), or an experimental DMS/greetd setup for manual session switching
 - **GPU**: AMD (discrete or APU), NVIDIA (discrete), or Intel (Arc / Iris Xe), or any hybrid combo of the above
   - Intel Arc (Alchemist, Battlemage): well-supported
   - Tiger Lake / Alder Lake Iris Xe: playable for indies / older AAA
@@ -129,7 +135,7 @@ Switching between modes is seamless — SDDM handles session transitions, and yo
   - Hybrid laptops (NVIDIA + iGPU, AMD dGPU + iGPU): use the corresponding `[hybrid-*]` GPU mode in the Settings TUI
 - **AUR Helper**: yay or paru (for ChimeraOS session packages)
 
-> **Note**: This script targets Omarchy and its stack (Hyprland, SDDM, iwd, UWSM, PipeWire). It works on other Arch + Hyprland setups with light tweaks, but isn't tested there.
+> **Note**: This script targets Omarchy and its stack (Hyprland, SDDM, iwd, UWSM, PipeWire). The DMS/greetd backend is experimental and currently manual-only.
 
 ## Quick Start
 
@@ -234,9 +240,11 @@ Package installs use Omarchy's `omarchy-pkg-add` (idempotent, double-checks pacm
 | Path | Purpose |
 |---|---|
 | `/usr/local/bin/switch-to-gaming` | Hyprland → Gaming Mode |
-| `/usr/local/bin/switch-to-desktop` | Gaming Mode → Hyprland (synchronous power-state restore + atomic SDDM restart) |
+| `/usr/local/bin/switch-to-desktop` | Gaming Mode → Hyprland (synchronous power-state restore + backend transition) |
 | `/usr/local/bin/gamescope-session-nm-wrapper` | Main session wrapper (performance mode, NM, drive mounting, saves pre-Gaming-Mode state) |
-| `/usr/local/bin/gaming-session-switch` | Helper that toggles SDDM autologin between Hyprland and Gamescope |
+| `/usr/local/bin/deckshift-session-switch` | Backend-neutral helper that selects desktop or gaming session |
+| `/usr/local/bin/deckshift-session-transition` | Backend-neutral helper that restarts SDDM or exits to DMS greeter |
+| `/usr/local/bin/gaming-session-switch` | Compatibility wrapper for `deckshift-session-switch` |
 | `/usr/local/bin/gaming-keybind-monitor` | Python evdev daemon catching `Super+Shift+R` inside Gamescope |
 | `/usr/lib/os-session-select` | Handler for Steam's "Exit to Desktop" button |
 | `/usr/local/lib/gamescope-nvidia/gamescope` | NVIDIA wrapper that adds `--force-composition` |
@@ -257,8 +265,10 @@ Package installs use Omarchy's `omarchy-pkg-add` (idempotent, double-checks pacm
 #### Session & Display Manager
 | Path | Purpose |
 |---|---|
-| `/usr/share/wayland-sessions/gamescope-session-steam-nm.desktop` | SDDM session entry for Gaming Mode |
+| `/usr/share/wayland-sessions/gamescope-session-steam-nm.desktop` | Wayland session entry for Gaming Mode |
-| `/etc/sddm.conf.d/zz-gaming-session.conf` | SDDM autologin session switching config |
+| `/etc/deckshift/session-backend.conf` | Active session backend and session IDs |
+| `/etc/sddm.conf.d/zz-gaming-session.conf` | SDDM autologin session switching config when using the SDDM backend |
+| `/var/cache/dms-greeter/.local/state/memory.json` | DMS greeter memory updated when using the DMS manual backend |
 
 #### Permissions & Security
 | Path | Purpose |
@@ -300,8 +310,8 @@ Desktop Mode (Hyprland)
     ├─ Super+Shift+S pressed
     │   └─ switch-to-gaming runs:
     │       ├─ Masks suspend targets (prevents sleep during switch)
-    │       ├─ Updates SDDM config to gaming session
+    │       ├─ Selects the gaming session through deckshift-session-switch
-    │       └─ Restarts SDDM → boots into Gaming Mode
+    │       └─ Runs deckshift-session-transition
     │
 Gaming Mode (Gamescope + Steam Big Picture)
     │
@@ -320,8 +330,8 @@ Gaming Mode (Gamescope + Steam Big Picture)
     │       ├─ Restores Bluetooth
     │       ├─ Shuts down Steam gracefully
     │       ├─ Kills gamescope
-    │       ├─ Updates SDDM config to Hyprland session
+    │       ├─ Selects the desktop session through deckshift-session-switch
-    │       └─ Atomic systemctl restart sddm → boots into Desktop Mode
+    │       └─ Runs deckshift-session-transition
     │
     └─ On session cleanup (trap handler — backup path):
         ├─ Kills steam-library-mount and keybind-monitor
@@ -553,7 +563,8 @@ sudo pkill -f steam-library-mount
 
 # Remove scripts
 sudo rm -f /usr/local/bin/{switch-to-gaming,switch-to-desktop,gamescope-session-nm-wrapper,\
-gaming-session-switch,gaming-keybind-monitor,gamescope-nm-start,gamescope-nm-stop,\
+deckshift-session-switch,deckshift-session-transition,gaming-session-switch,\
+gaming-keybind-monitor,gamescope-nm-start,gamescope-nm-stop,\
 steam-library-mount,deckshift-settings}
 sudo rm -f /usr/lib/os-session-select
 sudo rm -rf /usr/local/lib/gamescope-nvidia
@@ -572,6 +583,7 @@ sudo rm -f /etc/udev/rules.d/99-gaming-performance.rules
 sudo rm -f /etc/security/limits.d/99-gaming-memlock.conf
 
 # Remove configs
+sudo rm -rf /etc/deckshift
 sudo rm -f /etc/sddm.conf.d/zz-gaming-session.conf
 sudo rm -f /etc/environment.d/99-shader-cache.conf
 sudo rm -f /etc/environment.d/90-nvidia-gamescope.conf

deckshift.sh

@@ -48,6 +48,9 @@ CONFIG_FILE="/etc/gaming-mode.conf"
 [[ -f "$HOME/.gaming-mode.conf" ]] && CONFIG_FILE="$HOME/.gaming-mode.conf"
 source "$CONFIG_FILE" 2>/dev/null || true
 : "${PERFORMANCE_MODE:=enabled}"
+: "${DECKSHIFT_SESSION_BACKEND:=auto}"
+: "${DECKSHIFT_DESKTOP_SESSION_ID:=hyprland-uwsm.desktop}"
+: "${DECKSHIFT_GAMING_SESSION_ID:=gamescope-session-steam-nm.desktop}"
 
 # Flags that track whether the user needs to reboot or re-login after setup.
 # Various steps set these to 1 when they make changes that only take effect
@@ -1321,10 +1324,10 @@ setup_settings_tui() {
 # to seamlessly switch between Desktop Mode (Hyprland) and Gaming Mode
 # (Gamescope + Steam Big Picture).
 #
-# The switching mechanism works through SDDM (the display/login manager):
+# The switching mechanism works through a session backend:
 #   1. User presses Super+Shift+S in Hyprland
-#   2. switch-to-gaming script updates SDDM config to point to Gaming session
+#   2. switch-to-gaming selects the Gaming Mode session
-#   3. SDDM restarts and auto-logs into the Gaming Mode session
+#   3. The backend transitions through SDDM or the configured greeter
 #   4. gamescope-session-nm-wrapper starts performance tuning, NetworkManager,
 #      drive mounting, keybind monitor, then launches Gamescope + Steam
 #   5. When done (Super+Shift+R or Steam > Exit to Desktop), the reverse happens
@@ -1335,7 +1338,7 @@ setup_settings_tui() {
 #   - Keybind monitor (Python daemon using evdev for Super+Shift+R)
 #   - NetworkManager start/stop scripts (iwd <-> NM handoff)
 #   - Steam library auto-mount daemon
-#   - SDDM session entry and config
+#   - Session entry, backend config, and display-manager helpers
 #   - Polkit and sudoers rules for passwordless operation
 #   - Hyprland keybind for Super+Shift+S
 #
@@ -1431,6 +1434,50 @@ PY
   info "Patched $gsp — CUSTOM_REFRESH_RATES now reaches gamescope via --nested-refresh"
 }
 
+detect_session_backend() {
+  case "${DECKSHIFT_SESSION_BACKEND}" in
+    sddm|dms-greeter-manual)
+      printf '%s\n' "$DECKSHIFT_SESSION_BACKEND"
+      return 0
+      ;;
+    auto)
+      ;;
+    *)
+      die "Unsupported DECKSHIFT_SESSION_BACKEND: $DECKSHIFT_SESSION_BACKEND"
+      ;;
+  esac
+
+  local display_manager=""
+  if [[ -L /etc/systemd/system/display-manager.service ]]; then
+    display_manager=$(basename "$(readlink -f /etc/systemd/system/display-manager.service)" 2>/dev/null || true)
+  fi
+
+  if [[ "$display_manager" == "greetd.service" ]] &&
+     [[ -r /etc/greetd/config.toml ]] &&
+     grep -q 'dms-greeter' /etc/greetd/config.toml; then
+    printf '%s\n' "dms-greeter-manual"
+    return 0
+  fi
+
+  printf '%s\n' "sddm"
+}
+
+read_installed_session_backend() {
+  local conf="/etc/deckshift/session-backend.conf"
+  if [[ -r "$conf" ]]; then
+    local installed_backend
+    installed_backend=$(sed -n 's/^DECKSHIFT_SESSION_BACKEND=//p' "$conf" 2>/dev/null | head -1)
+    case "$installed_backend" in
+      sddm|dms-greeter-manual)
+        printf '%s\n' "$installed_backend"
+        return 0
+        ;;
+    esac
+  fi
+
+  detect_session_backend
+}
+
 setup_session_switching() {
   echo ""
   echo "================================================================"
@@ -1471,6 +1518,10 @@ setup_session_switching() {
   local current_user="${SUDO_USER:-$USER}"
   local user_home
   user_home=$(eval echo "~$current_user")
+  local session_backend
+  session_backend=$(detect_session_backend)
+  local gaming_session_path="/usr/share/wayland-sessions/${DECKSHIFT_GAMING_SESSION_ID}"
+  info "Using session backend: $session_backend"
 
   # GPU detection only — the installer no longer chooses a monitor, resolution
   # or refresh rate. Those are user choices, made later via Walker → "DeckShift
@@ -2285,14 +2336,13 @@ NM_WRAPPER
   sudo chmod +x "$nm_wrapper"
   info "Created $nm_wrapper"
 
-  # SDDM Session Entry
+  # Gaming Session Entry
   #
-  # SDDM (the login/display manager) needs a .desktop file to know about
+  # Display managers and greeters need a .desktop file to know about Gaming
-  # Gaming Mode as a session option. This is what tells SDDM "when you
+  # Mode as a session option. The active session backend selects this entry
-  # auto-login to the gaming session, run this script." It's placed in
+  # when switching into Gaming Mode.
-  # /usr/share/wayland-sessions/ alongside the normal Hyprland session.
+  info "Creating Gaming Mode session entry..."
-  info "Creating SDDM session entry..."
+  local session_desktop="$gaming_session_path"
-  local session_desktop="/usr/share/wayland-sessions/gamescope-session-steam-nm.desktop"
 
   sudo tee "$session_desktop" > /dev/null << 'SESSION_DESKTOP'
 [Desktop Entry]
@@ -2310,19 +2360,19 @@ SESSION_DESKTOP
   # When you click Steam > Power > "Exit to Desktop" inside Gaming Mode,
   # Steam calls /usr/lib/os-session-select. On a real Steam Deck this
   # switches to Desktop Mode. Our version does the same thing — it updates
-  # SDDM to boot back into Hyprland and restarts the display manager.
+  # selects the desktop session and asks the active backend to transition.
   info "Creating session-select script..."
   local os_session_select="/usr/lib/os-session-select"
 
   sudo tee "$os_session_select" > /dev/null << 'OS_SESSION_SELECT'
 #!/bin/bash
 rm -f /tmp/.gaming-session-active
-sudo -n /usr/local/bin/gaming-session-switch desktop 2>/dev/null || {
+sudo -n /usr/local/bin/deckshift-session-switch desktop 2>/dev/null || {
   echo "Warning: Failed to update session config"
 }
 timeout 5 steam -shutdown 2>/dev/null || true
 sleep 1
-nohup sudo -n systemctl restart sddm &>/dev/null &
+nohup /usr/local/bin/deckshift-session-transition desktop &>/dev/null &
 disown
 exit 0
 OS_SESSION_SELECT
@@ -2335,10 +2385,10 @@ OS_SESSION_SELECT
   # This script handles the transition from Desktop to Gaming Mode:
   #   1. Masks suspend targets — prevents the system from sleeping when the
   #      monitor briefly disconnects during the display manager restart
-  #   2. Updates SDDM config to auto-login to the gaming session
+  #   2. Selects the gaming session through DeckShift's active backend
   #   3. Kills any leftover gamescope processes from a previous session
   #   4. Switches to VT2 (virtual terminal) to avoid display conflicts
-  #   5. Restarts SDDM, which auto-logs into Gaming Mode
+  #   5. Transitions through SDDM or the configured greeter
   info "Creating switch-to-gaming script..."
   local switch_script="/usr/local/bin/switch-to-gaming"
 
@@ -2346,7 +2396,7 @@ OS_SESSION_SELECT
 #!/bin/bash
 # Inhibit suspend FIRST - prevents suspend when monitor detaches during switch
 sudo -n systemctl mask --runtime sleep.target suspend.target hibernate.target hybrid-sleep.target 2>/dev/null
-sudo -n /usr/local/bin/gaming-session-switch gaming 2>/dev/null || {
+sudo -n /usr/local/bin/deckshift-session-switch gaming 2>/dev/null || {
   notify-send -u critical -t 3000 "Gaming Mode" "Failed to update session config" 2>/dev/null || true
 }
 notify-send -u normal -t 2000 "Gaming Mode" "Switching to Gaming Mode..." 2>/dev/null || true
@@ -2377,7 +2427,7 @@ fi
 
 sudo -n chvt 2 2>/dev/null || true
 sleep 0.3
-sudo -n systemctl restart sddm
+/usr/local/bin/deckshift-session-transition gaming
 SWITCH_SCRIPT
 
   sudo chmod +x "$switch_script"
@@ -2390,8 +2440,8 @@ SWITCH_SCRIPT
   #   2. Restores Bluetooth (disabled during gaming to reduce interference)
   #   3. Gracefully shuts down Steam (timeout 5s, then force kill)
   #   4. Kills gamescope with SIGTERM first, then SIGKILL if it won't die
-  #   5. Updates SDDM config back to Hyprland session
+  #   5. Selects the desktop session through DeckShift's active backend
-  #   6. Restarts SDDM, which auto-logs into Desktop Mode
+  #   6. Transitions through SDDM or the configured greeter
   info "Creating switch-to-desktop script..."
   local switch_desktop_script="/usr/local/bin/switch-to-desktop"
 
@@ -2429,7 +2479,7 @@ fi
 sudo -n systemctl unmask sleep.target suspend.target hibernate.target hybrid-sleep.target 2>/dev/null
 sudo -n systemctl unmask --runtime sleep.target suspend.target hibernate.target hybrid-sleep.target 2>/dev/null
 sudo -n systemctl daemon-reload 2>/dev/null
-sudo -n /usr/local/bin/gaming-session-switch desktop 2>/dev/null || true
+sudo -n /usr/local/bin/deckshift-session-switch desktop 2>/dev/null || true
 
 # Re-enable Bluetooth
 sudo -n /usr/bin/rfkill unblock bluetooth 2>/dev/null || true
@@ -2465,9 +2515,10 @@ sudo -n chvt 2 2>/dev/null || true
 sleep 0.5
 # Atomic restart — stop+start (with stop and start as separate sudo calls)
 # was unreliable: stop/start aren't NOPASSWD-allowed individually (only
-# `restart` is), and the disowned `start` could be killed by session teardown
+# `restart` is for SDDM), and the disowned `start` could be killed by session
-# before SDDM actually came back up, leaving the user on a black screen.
+# teardown before the display manager actually came back up, leaving the user
-sudo -n systemctl restart sddm
+# on a black screen.
+/usr/local/bin/deckshift-session-transition desktop
 exit 0
 SWITCH_DESKTOP
 
@@ -2661,21 +2712,14 @@ HYPR_PORTAL
     warn "Add manually: exec-once = /usr/local/bin/deckshift-portal-recovery"
   fi
 
-  # SDDM Session Switching Config
+  # Session Backend Config
   #
-  # SDDM supports auto-login — it can automatically log in a user to a
+  # Keep display-manager-specific behavior behind small helpers so DeckShift's
-  # specific session without showing the login screen. This config file
+  # Gamescope, Steam, GPU, and performance logic can stay backend-agnostic.
-  # controls WHICH session SDDM auto-logs into.
+  info "Creating session backend config..."
-  #
+  local deckshift_config_dir="/etc/deckshift"
-  # The switching mechanism works by editing this file:
+  local deckshift_backend_conf="${deckshift_config_dir}/session-backend.conf"
-  #   - "Session=hyprland-uwsm" → boots into Desktop Mode
+  sudo install -d -m 0755 "$deckshift_config_dir"
-  #   - "Session=gamescope-session-steam-nm" → boots into Gaming Mode
-  #
-  # The gaming-session-switch helper script toggles this value, then SDDM
-  # is restarted to pick up the change. The "zz-" prefix ensures this
-  # config loads LAST and overrides any other SDDM autologin settings.
-  info "Creating SDDM session switching config..."
-  local sddm_gaming_conf="/etc/sddm.conf.d/zz-gaming-session.conf"
 
   local autologin_user="$current_user"
   if [[ -f /etc/sddm.conf.d/autologin.conf ]]; then
@@ -2683,49 +2727,198 @@ HYPR_PORTAL
     [[ -z "$autologin_user" ]] && autologin_user="$current_user"
   fi
 
+  sudo tee "$deckshift_backend_conf" > /dev/null << BACKEND_CONF
+DECKSHIFT_SESSION_BACKEND=${session_backend}
+DECKSHIFT_DESKTOP_SESSION_ID=${DECKSHIFT_DESKTOP_SESSION_ID}
+DECKSHIFT_GAMING_SESSION_ID=${DECKSHIFT_GAMING_SESSION_ID}
+DECKSHIFT_GAMING_SESSION_PATH=${gaming_session_path}
+DECKSHIFT_SDDM_CONF=/etc/sddm.conf.d/zz-gaming-session.conf
+DECKSHIFT_SDDM_USER=${autologin_user}
+DECKSHIFT_DMS_MEMORY_FILE=/var/cache/dms-greeter/.local/state/memory.json
+DECKSHIFT_DMS_GREETER_GROUP=greeter
+BACKEND_CONF
+  sudo chmod 0644 "$deckshift_backend_conf"
+
+  info "Created $deckshift_backend_conf"
+
+  if [[ "$session_backend" == "sddm" ]]; then
+    info "Creating SDDM session switching config..."
+    local sddm_gaming_conf="/etc/sddm.conf.d/zz-gaming-session.conf"
+    sudo install -d -m 0755 /etc/sddm.conf.d
     sudo tee "$sddm_gaming_conf" > /dev/null << SDDM_GAMING
 [Autologin]
 User=${autologin_user}
-Session=hyprland-uwsm
+Session=${DECKSHIFT_DESKTOP_SESSION_ID%.desktop}
 Relogin=true
 SDDM_GAMING
-
     info "Created $sddm_gaming_conf"
+  else
+    info "DMS greeter backend selected; SDDM autologin config will not be created"
+  fi
 
-  info "Creating session switching helper script..."
+  info "Creating session switching helper scripts..."
-  local session_helper="/usr/local/bin/gaming-session-switch"
+  local session_helper="/usr/local/bin/deckshift-session-switch"
 
   sudo tee "$session_helper" > /dev/null << 'SESSION_HELPER'
 #!/bin/bash
-CONF="/etc/sddm.conf.d/zz-gaming-session.conf"
+set -euo pipefail
+
+CONF="/etc/deckshift/session-backend.conf"
 if [[ ! -f "$CONF" ]]; then
   echo "Error: Config file not found: $CONF" >&2
   exit 1
 fi
 
-case "$1" in
+# shellcheck disable=SC1090
-  gaming)
+source "$CONF"
-    sed -i 's/^Session=.*/Session=gamescope-session-steam-nm/' "$CONF"
+
-    echo "Session set to: gaming mode"
+target="${1:-}"
-    ;;
+case "$target" in
-  desktop)
+  gaming|desktop) ;;
-    sed -i 's/^Session=.*/Session=hyprland-uwsm/' "$CONF"
-    echo "Session set to: desktop mode"
-    ;;
   *)
     echo "Usage: $0 {gaming|desktop}" >&2
     exit 1
     ;;
 esac
+
+session_id_for_target() {
+  case "$1" in
+    gaming) printf '%s\n' "$DECKSHIFT_GAMING_SESSION_ID" ;;
+    desktop) printf '%s\n' "$DECKSHIFT_DESKTOP_SESSION_ID" ;;
+  esac
+}
+
+resolve_session_path() {
+  local session_id="$1"
+  local explicit=""
+  if [[ "$session_id" == "$DECKSHIFT_GAMING_SESSION_ID" ]]; then
+    explicit="${DECKSHIFT_GAMING_SESSION_PATH:-}"
+  fi
+
+  if [[ -n "$explicit" && -f "$explicit" ]]; then
+    printf '%s\n' "$explicit"
+    return 0
+  fi
+
+  local dir candidate
+  for dir in /usr/local/share/wayland-sessions /usr/share/wayland-sessions; do
+    candidate="${dir}/${session_id}"
+    if [[ -f "$candidate" ]]; then
+      printf '%s\n' "$candidate"
+      return 0
+    fi
+  done
+
+  echo "Error: session file not found for ${session_id}" >&2
+  exit 1
+}
+
+write_dms_memory() {
+  local session_id="$1"
+  local session_path="$2"
+  local memory_file="${DECKSHIFT_DMS_MEMORY_FILE:-/var/cache/dms-greeter/.local/state/memory.json}"
+  local tmp
+  tmp=$(mktemp)
+
+  python3 - "$memory_file" "$session_path" "$session_id" > "$tmp" <<'PY'
+import json
+import os
+import sys
+
+path, session_path, session_id = sys.argv[1:4]
+data = {}
+try:
+    if os.path.exists(path):
+        with open(path) as fh:
+            loaded = json.load(fh)
+        if isinstance(loaded, dict):
+            data = loaded
+except Exception:
+    data = {}
+
+data["lastSessionId"] = session_path
+data["lastSessionDesktopId"] = session_id
+json.dump(data, sys.stdout, indent=2)
+sys.stdout.write("\n")
+PY
+
+  install -d -m 0775 "$(dirname "$memory_file")"
+  install -m 0664 "$tmp" "$memory_file"
+  rm -f "$tmp"
+
+  if getent group "${DECKSHIFT_DMS_GREETER_GROUP:-greeter}" >/dev/null 2>&1; then
+    chgrp "${DECKSHIFT_DMS_GREETER_GROUP:-greeter}" "$(dirname "$memory_file")" "$memory_file" || true
+  fi
+}
+
+session_id="$(session_id_for_target "$target")"
+
+case "${DECKSHIFT_SESSION_BACKEND:-sddm}" in
+  sddm)
+    sddm_conf="${DECKSHIFT_SDDM_CONF:-/etc/sddm.conf.d/zz-gaming-session.conf}"
+    if [[ ! -f "$sddm_conf" ]]; then
+      echo "Error: SDDM config file not found: $sddm_conf" >&2
+      exit 1
+    fi
+    sed -i "s/^Session=.*/Session=${session_id%.desktop}/" "$sddm_conf"
+    ;;
+  dms-greeter-manual)
+    session_path="$(resolve_session_path "$session_id")"
+    write_dms_memory "$session_id" "$session_path"
+    ;;
+  *)
+    echo "Error: unsupported DeckShift session backend: ${DECKSHIFT_SESSION_BACKEND:-}" >&2
+    exit 1
+    ;;
+esac
+
+echo "Session set to: ${target} mode"
 SESSION_HELPER
 
   sudo chmod +x "$session_helper"
   info "Created $session_helper"
 
+  local legacy_session_helper="/usr/local/bin/gaming-session-switch"
+  sudo tee "$legacy_session_helper" > /dev/null << 'LEGACY_SESSION_HELPER'
+#!/bin/bash
+exec /usr/local/bin/deckshift-session-switch "$@"
+LEGACY_SESSION_HELPER
+  sudo chmod +x "$legacy_session_helper"
+  info "Created compatibility wrapper $legacy_session_helper"
+
+  local transition_helper="/usr/local/bin/deckshift-session-transition"
+  sudo tee "$transition_helper" > /dev/null << 'TRANSITION_HELPER'
+#!/bin/bash
+set -euo pipefail
+
+CONF="/etc/deckshift/session-backend.conf"
+[[ -f "$CONF" ]] || { echo "Error: Config file not found: $CONF" >&2; exit 1; }
+# shellcheck disable=SC1090
+source "$CONF"
+
+case "${DECKSHIFT_SESSION_BACKEND:-sddm}" in
+  sddm)
+    exec sudo -n systemctl restart sddm
+    ;;
+  dms-greeter-manual)
+    if [[ -n "${XDG_SESSION_ID:-}" ]]; then
+      exec loginctl terminate-session "$XDG_SESSION_ID"
+    fi
+    exec sudo -n systemctl restart greetd.service
+    ;;
+  *)
+    echo "Error: unsupported DeckShift session backend: ${DECKSHIFT_SESSION_BACKEND:-}" >&2
+    exit 1
+    ;;
+esac
+TRANSITION_HELPER
+  sudo chmod +x "$transition_helper"
+  info "Created $transition_helper"
+
   # Sudoers Rules for Session Switching
   #
   # The session switching scripts need to run several commands as root
-  # (restart SDDM, start/stop NetworkManager, control Bluetooth, etc.).
+  # (restart display managers, start/stop NetworkManager, control Bluetooth, etc.).
   # These sudoers rules allow members of the "video" and "wheel" groups
   # to run ONLY these specific commands without a password.
   #
@@ -2744,7 +2937,10 @@ SESSION_HELPER
   local switch_output
   switch_output=$(sudo tee "$sudoers_session" << 'SUDOERS_SWITCH' 2>&1
 %video ALL=(ALL) NOPASSWD: /usr/local/bin/gaming-session-switch
+%video ALL=(ALL) NOPASSWD: /usr/local/bin/deckshift-session-switch
+%video ALL=(ALL) NOPASSWD: /usr/local/bin/deckshift-session-transition
 %video ALL=(ALL) NOPASSWD: /usr/bin/systemctl restart sddm
+%video ALL=(ALL) NOPASSWD: /usr/bin/systemctl restart greetd.service
 %video ALL=(ALL) NOPASSWD: /usr/bin/chvt
 %video ALL=(ALL) NOPASSWD: /usr/bin/systemctl mask --runtime sleep.target suspend.target hibernate.target hybrid-sleep.target
 %video ALL=(ALL) NOPASSWD: /usr/bin/systemctl unmask sleep.target suspend.target hibernate.target hybrid-sleep.target
@@ -2846,10 +3042,13 @@ HYPR_GAMING
   echo "  Files created/modified:"
   echo "    - ~/.config/environment.d/gamescope-session-plus.conf"
   echo "    - /usr/local/bin/gamescope-session-nm-wrapper"
-  echo "    - /usr/share/wayland-sessions/gamescope-session-steam-nm.desktop"
+  echo "    - ${gaming_session_path}"
   echo "    - /usr/lib/os-session-select"
   echo "    - /usr/local/bin/switch-to-gaming"
   echo "    - /usr/local/bin/switch-to-desktop"
+  echo "    - /usr/local/bin/deckshift-session-switch"
+  echo "    - /usr/local/bin/deckshift-session-transition"
+  echo "    - /etc/deckshift/session-backend.conf (${session_backend})"
   echo "    - /usr/local/bin/gaming-keybind-monitor (Super+Shift+R)"
   echo "    - ~/.config/hypr/bindings.conf (keybind added)"
   echo ""
@@ -2910,10 +3109,14 @@ verify_installation() {
   local all_ok=true
   local missing_files=()
   local permission_issues=()
+  local verify_session_backend
+  verify_session_backend=$(read_installed_session_backend)
 
   declare -A expected_files=(
     ["/usr/local/bin/gamescope-session-nm-wrapper"]="755:ChimeraOS session with NM wrapper"
     ["/usr/local/lib/gamescope-nvidia/gamescope"]="755:NVIDIA gamescope wrapper (--force-composition)"
+    ["/usr/local/bin/deckshift-session-switch"]="755:Backend-neutral session selector"
+    ["/usr/local/bin/deckshift-session-transition"]="755:Backend-neutral display-manager transition helper"
     ["/usr/local/bin/gaming-session-switch"]="755:Session switching helper (gaming/desktop)"
     ["/usr/lib/os-session-select"]="755:Steam Exit to Desktop handler"
     ["/usr/local/bin/switch-to-gaming"]="755:Hyprland to Gaming Mode switcher"
@@ -2927,8 +3130,9 @@ verify_installation() {
     ["/usr/bin/steamos-update"]="755:Steam compatibility (from AUR package)"
     ["/usr/bin/jupiter-biosupdate"]="755:Steam compatibility (from AUR package)"
     ["/usr/bin/steamos-select-branch"]="755:Steam compatibility (from AUR package)"
-    ["/usr/share/wayland-sessions/gamescope-session-steam-nm.desktop"]="644:SDDM session entry"
+    ["/usr/share/wayland-sessions/gamescope-session-steam-nm.desktop"]="644:Gaming Mode Wayland session entry"
     ["/usr/share/gamescope-session-plus/gamescope-session-plus"]="755:ChimeraOS session launcher (from AUR)"
+    ["/etc/deckshift/session-backend.conf"]="644:Session backend config"
     ["/etc/sddm.conf.d/zz-gaming-session.conf"]="644:SDDM session switching config"
     ["/etc/polkit-1/rules.d/50-gamescope-networkmanager.rules"]="644:Polkit NM rules"
     ["/etc/polkit-1/rules.d/50-udisks-gaming.rules"]="644:Polkit udisks2 rules (external drive mount)"
@@ -2953,7 +3157,16 @@ verify_installation() {
     local description="${expected_files[$file]#*:}"
     local is_optional=false
 
-    [[ "$description" == *"(optional)"* ]] && is_optional=true
+    case "$file" in
+      /etc/sddm.conf.d/zz-gaming-session.conf)
+        [[ "$verify_session_backend" == "dms-greeter-manual" ]] && is_optional=true
+        ;;
+      /etc/NetworkManager/conf.d/10-iwd-backend.conf|\
+      /etc/NetworkManager/conf.d/20-unmanaged-systemd.conf|\
+      /usr/share/libalpm/hooks/deckshift-gamescope-cap.hook)
+        is_optional=true
+        ;;
+    esac
 
     if sudo test -f "$file" 2>/dev/null; then
       local actual_perm
@@ -3112,6 +3325,48 @@ verify_installation() {
   echo "  systemd-networkd: $(systemctl is-active systemd-networkd.service 2>/dev/null || echo 'inactive')"
   echo "  polkit:         $(systemctl is-active polkit.service 2>/dev/null || echo 'inactive')"
 
+  if [[ "$verify_session_backend" == "dms-greeter-manual" ]]; then
+    echo ""
+    echo "  DMS GREETER BACKEND:"
+    echo "  --------------------"
+    local dms_memory_file="/var/cache/dms-greeter/.local/state/memory.json"
+    if [[ -r /etc/deckshift/session-backend.conf ]]; then
+      local configured_memory_file
+      configured_memory_file=$(sed -n 's/^DECKSHIFT_DMS_MEMORY_FILE=//p' /etc/deckshift/session-backend.conf 2>/dev/null | head -1)
+      [[ -n "$configured_memory_file" ]] && dms_memory_file="$configured_memory_file"
+    fi
+
+    echo "  Backend:         $verify_session_backend"
+    echo "  Memory file:     $dms_memory_file"
+    if [[ -r "$dms_memory_file" ]]; then
+      local memory_stat
+      memory_stat=$(stat -c "%U:%G %a" "$dms_memory_file" 2>/dev/null || echo "unknown")
+      echo "  ✓ DMS memory readable ($memory_stat)"
+      if python3 - "$dms_memory_file" <<'PY'
+import json
+import sys
+
+with open(sys.argv[1]) as fh:
+    data = json.load(fh)
+if not isinstance(data, dict):
+    raise SystemExit(1)
+for key in ("lastSessionId", "lastSessionDesktopId"):
+    value = data.get(key)
+    if not isinstance(value, str) or not value:
+        raise SystemExit(1)
+PY
+      then
+        echo "  ✓ DMS memory has lastSessionId and lastSessionDesktopId"
+      else
+        echo "  ✗ DMS memory JSON is missing expected session keys"
+        all_ok=false
+      fi
+    else
+      echo "  ✗ DMS memory file is not readable"
+      all_ok=false
+    fi
+  fi
+
   echo ""
   echo "  SUDO PERMISSIONS TEST:"
   echo "  ----------------------"

docs/session-backend-handoff.md

@@ -0,0 +1,423 @@
+# DeckShift Session Backend Handoff
+
+Last updated: 2026-07-11.
+
+## Goal
+
+Extend DeckShift so its Steam Deck-style gaming mode is not hard-wired to SDDM.
+The first target is to preserve the existing SDDM behavior for upstream/Omarchy
+users while adding a DMS/greetd manual backend for our Hyprland/DMS dotfiles.
+
+The long-term goal is:
+
+- `sddm`: existing seamless auto-login flow for Omarchy users.
+- `dms-greeter-manual`: select the next session through DMS greeter memory and
+  require normal greeter authentication.
+- Later: a host-gated one-shot auto-login backend for living-room machines, if
+  it can be made safe and recoverable.
+
+## Repository State
+
+Local checkout:
+
+```text
+/home/anodyine/Projects/deckshift
+```
+
+Current work branch:
+
+```text
+feature/session-backends
+```
+
+Remotes:
+
+```text
+origin   ssh://git@tea.kyle-merritt.com:2222/anodyine/deckshift.git
+github   https://github.com/Anodyine/deckshift.git
+upstream https://github.com/28allday/deckshift.git
+```
+
+`origin` is the Gitea working remote. `github` is the public fork. `upstream`
+is fetch-only for the original DeckShift project.
+
+## What Changed So Far
+
+All code changes so far are in:
+
+```text
+deckshift.sh
+README.md
+```
+
+### Installer Configuration
+
+`deckshift.sh` now accepts these variables:
+
+```sh
+DECKSHIFT_SESSION_BACKEND=auto
+DECKSHIFT_DESKTOP_SESSION_ID=hyprland-uwsm.desktop
+DECKSHIFT_GAMING_SESSION_ID=gamescope-session-steam-nm.desktop
+```
+
+Supported backend values right now:
+
+```text
+auto
+sddm
+dms-greeter-manual
+```
+
+`auto` detects DMS/greetd when:
+
+- `/etc/systemd/system/display-manager.service` resolves to `greetd.service`.
+- `/etc/greetd/config.toml` contains `dms-greeter`.
+
+Otherwise it falls back to `sddm`.
+
+### Generated Backend Config
+
+The installer writes:
+
+```text
+/etc/deckshift/session-backend.conf
+```
+
+It records the active backend, desktop/gaming session IDs, the Gamescope session
+file path, SDDM config path, and DMS greeter memory path.
+
+### Generated Helpers
+
+The old SDDM-specific calls are now routed through backend-neutral helpers:
+
+```text
+/usr/local/bin/deckshift-session-switch
+/usr/local/bin/deckshift-session-transition
+```
+
+`/usr/local/bin/gaming-session-switch` is still generated as a compatibility
+wrapper that execs `deckshift-session-switch`.
+
+Existing generated scripts now call the backend-neutral helpers:
+
+```text
+/usr/lib/os-session-select
+/usr/local/bin/switch-to-gaming
+/usr/local/bin/switch-to-desktop
+```
+
+### SDDM Backend Behavior
+
+The SDDM backend preserves the previous model:
+
+1. Write or update `/etc/sddm.conf.d/zz-gaming-session.conf`.
+2. `deckshift-session-switch gaming|desktop` changes `Session=...`.
+3. `deckshift-session-transition` runs `sudo -n systemctl restart sddm`.
+
+This should be behaviorally equivalent to the original DeckShift flow.
+
+### DMS Manual Backend Behavior
+
+The DMS manual backend does not create SDDM config.
+
+`deckshift-session-switch gaming|desktop`:
+
+1. Resolves the target session file from an allowlist:
+   - desktop: `DECKSHIFT_DESKTOP_SESSION_ID`
+   - gaming: `DECKSHIFT_GAMING_SESSION_ID`
+2. Looks in:
+   - `/usr/local/share/wayland-sessions`
+   - `/usr/share/wayland-sessions`
+3. Writes DMS greeter memory:
+
+   ```text
+   /var/cache/dms-greeter/.local/state/memory.json
+   ```
+
+4. Preserves any existing JSON keys and updates:
+   - `lastSessionId`
+   - `lastSessionDesktopId`
+
+`deckshift-session-transition`:
+
+1. If `XDG_SESSION_ID` exists, runs:
+
+   ```sh
+   loginctl terminate-session "$XDG_SESSION_ID"
+   ```
+
+2. If there is no current session ID, falls back to:
+
+   ```sh
+   sudo -n systemctl restart greetd.service
+   ```
+
+This intentionally returns the user to the DMS greeter for normal
+authentication. It is not a one-shot auto-login implementation.
+
+### Sudoers
+
+The generated sudoers file now includes NOPASSWD entries for:
+
+```text
+/usr/local/bin/deckshift-session-switch
+/usr/local/bin/deckshift-session-transition
+/usr/bin/systemctl restart sddm
+/usr/bin/systemctl restart greetd.service
+```
+
+The existing compatibility and NetworkManager/Bluetooth rules remain.
+
+### README
+
+The README now documents:
+
+- The experimental DMS/greetd manual backend.
+- The new backend config and helper files.
+- The backend-neutral session switching flow.
+- Updated uninstall cleanup for `/etc/deckshift` and the new helper scripts.
+
+## Validation Already Run
+
+These checks passed:
+
+```sh
+bash -n deckshift.sh
+git diff --check
+```
+
+The generated heredoc scripts were also extracted and syntax-checked with
+`bash -n`:
+
+- `deckshift-session-switch`
+- `deckshift-session-transition`
+- `switch-to-gaming`
+- `switch-to-desktop`
+- `os-session-select`
+- `gaming-session-switch` compatibility wrapper
+
+`shellcheck` was not installed on this machine, so it has not been run yet.
+
+No installer run has been performed. No live `/etc`, `/usr/local/bin`, greeter,
+or display-manager state was changed by this work.
+
+### DMS Greeter Selection Probe
+
+After the first code pass, a manual DMS greeter selection test was run outside
+this checkout. The greeter selected the expected `Deckshift dms test` session.
+
+That confirms the core DMS manual backend assumption still holds: writing DMS
+greeter memory can preselect a non-SDDM session for the next login. This does
+not yet prove the full DeckShift-generated helper flow or Gamescope session
+entry, but it is the right green light for implementing and testing the manual
+DMS backend path before any auto-login work.
+
+### DMS Generated Helper Probe
+
+The generated helper path was then tested manually:
+
+```sh
+sudo -n /usr/local/bin/deckshift-session-switch gaming
+/usr/local/bin/deckshift-session-transition gaming
+```
+
+It behaved as expected: the current session exited, DMS greeter appeared, and
+the target gaming session was preselected.
+
+This proves the first real DMS manual backend flow at the DeckShift helper
+layer. Remaining DMS validation should focus on the full `switch-to-gaming`
+script, Gamescope/Steam session startup, and the return path back to the
+Hyprland UWSM desktop session.
+
+### DMS Manual Round Trip
+
+The DMS manual backend was also tested in both directions. It successfully
+switched the greeter selection away from Hyprland UWSM and then back to the
+Hyprland UWSM session. The user was able to log back into the UWSM desktop.
+
+This proves the non-SDDM manual session-selection loop:
+
+```text
+Hyprland UWSM -> selected gaming/test session -> DMS greeter
+DMS greeter/session -> selected Hyprland UWSM -> DMS greeter -> Hyprland UWSM
+```
+
+The next layer to test is no longer DMS memory/session preselection. It is the
+real DeckShift gaming session: `switch-to-gaming`, Gamescope/Steam startup, and
+`switch-to-desktop` return behavior.
+
+## Important Constraints
+
+Do not implement one-shot DMS auto-login yet. Manual DMS switching is the first
+safe milestone.
+
+Do not make this dotfiles-specific inside DeckShift. The DeckShift fork should
+grow generic backend seams; the dotfiles repo can decide whether and how to
+install/use the DMS backend.
+
+Keep the SDDM behavior stable for existing users. The backend abstraction should
+be boring and low-risk for the default Omarchy path.
+
+## Known Gaps And Risks
+
+### Not Tested Live
+
+The backend helpers have only been syntax-checked. They still need live testing
+on:
+
+- An SDDM/Omarchy machine or VM.
+- A DMS/greetd machine or VM.
+- A real target host with Gamescope/Steam.
+
+### DMS Memory Contract
+
+The DMS greeter memory write is based on a local proof from the dotfiles repo:
+writing `lastSessionId` and `lastSessionDesktopId` successfully preselected a
+test session in DMS greeter.
+
+Still verify:
+
+- Ownership and permissions after DeckShift writes the file.
+- Whether DMS ever overwrites the file during greeter startup.
+- Whether preserving extra JSON keys is sufficient across DMS versions.
+
+### Transition Semantics
+
+For DMS manual mode, `loginctl terminate-session "$XDG_SESSION_ID"` is preferred.
+The fallback `systemctl restart greetd.service` is more disruptive and should be
+treated as a fallback only.
+
+Verify whether `switch-to-desktop` from inside Gamescope has a valid
+`XDG_SESSION_ID`. If not, returning from gaming may restart greetd.
+
+### Session File Location
+
+The installer currently writes the gaming session to:
+
+```text
+/usr/share/wayland-sessions/gamescope-session-steam-nm.desktop
+```
+
+For our dotfiles, `/usr/local/share/wayland-sessions` may be a better long-term
+owner boundary. Decide whether DeckShift should make this configurable or leave
+the current upstream-compatible path alone.
+
+### Verification Mode
+
+`verify_installation` still treats `/etc/sddm.conf.d/zz-gaming-session.conf` as
+optional by description only. The verification logic marks missing optional
+files by checking whether the description contains `(optional)`, so this may
+need adjustment if verifying a DMS backend install.
+
+### Documentation Still Has Historical SDDM Mentions
+
+Some README changelog and troubleshooting sections still mention SDDM because
+they describe older releases or SDDM-specific recovery. That is probably fine,
+but before publishing this branch upstream, review the README for places where
+current behavior should say "session backend" instead.
+
+## Recommended Next Steps
+
+1. Install `shellcheck` on the dev machine or run it in a container/VM:
+
+   ```sh
+   shellcheck deckshift.sh
+   shellcheck bin/deckshift-settings
+   ```
+
+2. Test SDDM backend generation without changing behavior:
+
+   ```sh
+   DECKSHIFT_SESSION_BACKEND=sddm ./deckshift.sh
+   ```
+
+   Verify:
+
+   - `/etc/deckshift/session-backend.conf`
+   - `/etc/sddm.conf.d/zz-gaming-session.conf`
+   - `/usr/local/bin/deckshift-session-switch`
+   - `/usr/local/bin/deckshift-session-transition`
+   - Existing Super+Shift+S / Super+Shift+R behavior.
+
+3. Test DMS backend in the CachyOS/DMS VM or sacrificial host:
+
+   ```sh
+   DECKSHIFT_SESSION_BACKEND=dms-greeter-manual ./deckshift.sh
+   ```
+
+   Verify before switching:
+
+   - Gaming session appears in the DMS greeter session list.
+   - `deckshift-session-switch gaming` writes the expected DMS memory.
+   - `deckshift-session-switch desktop` restores the Hyprland UWSM session.
+   - File ownership/group/mode allow DMS greeter to read the memory file.
+
+4. Test DMS manual transition without Steam first:
+
+   ```sh
+   sudo -n /usr/local/bin/deckshift-session-switch gaming
+   /usr/local/bin/deckshift-session-transition gaming
+   ```
+
+   Expected result:
+
+   - Current session exits.
+   - DMS greeter appears.
+   - Gaming session is preselected.
+   - User must authenticate manually.
+
+5. Test return path:
+
+   ```sh
+   sudo -n /usr/local/bin/deckshift-session-switch desktop
+   /usr/local/bin/deckshift-session-transition desktop
+   ```
+
+   Expected result:
+
+   - Current session exits.
+   - DMS greeter appears.
+   - Hyprland UWSM is preselected.
+
+6. Only after manual DMS mode works, test full Gamescope/Steam entry and return.
+
+7. After both SDDM and DMS manual mode are proven, split large generated helper
+   bodies into clearer functions or files if desired. Avoid refactoring before
+   the behavior is proven.
+
+8. Add Gitea issues for follow-up work:
+
+   - Prove SDDM backend parity.
+   - Prove DMS manual backend in VM.
+   - Fix verification mode for backend-specific expected files.
+   - Decide session file owner path.
+   - Prototype one-shot DMS/greetd auto-login separately.
+
+## Recovery Notes For DMS Testing
+
+If a DMS switch leaves the host at the wrong selected session, switch to a TTY
+and write DMS memory back to Hyprland UWSM:
+
+```sh
+sudo python3 - <<'PY'
+import json
+path = "/var/cache/dms-greeter/.local/state/memory.json"
+data = {}
+try:
+    with open(path) as fh:
+        data = json.load(fh)
+except Exception:
+    pass
+data["lastSessionId"] = "/usr/local/share/wayland-sessions/hyprland-uwsm.desktop"
+data["lastSessionDesktopId"] = "hyprland-uwsm.desktop"
+with open(path, "w") as fh:
+    json.dump(data, fh, indent=2)
+    fh.write("\n")
+PY
+sudo chgrp greeter /var/cache/dms-greeter/.local/state /var/cache/dms-greeter/.local/state/memory.json 2>/dev/null || true
+sudo chmod 0664 /var/cache/dms-greeter/.local/state/memory.json
+sudo systemctl restart greetd.service
+```
+
+Do not rely on `chezmoi apply` as the only recovery path. The failure mode may
+be that the graphical desktop is unavailable.