Add SteamOS distro

Adds `--distro steamos` as a first-class build target. Pattern is the
same as bazzite-deck/batocera: distros/steamos/build-rootfs.sh fetches
the upstream rootfs (Valve's Steam Deck recovery .img.bz2 from
steamdeck-images.steamos.cloud), extracts the rootfs-A + var-A btrfs
slots into $CHROOT, swaps in our linux-ps5 kernel pkg.tar.zst, and
rebuilds the initramfs with the modules amdgpu needs for the PS5
Oberon GPU.

PS5-specific fixes applied to the SteamOS rootfs:

- Replace /usr/bin/steamos-session-select with a shim that writes
  /etc/sddm.conf.d/zzz-session-override.conf directly + restarts sddm.
  The vendored helper goes through steamosctl / steamos-manager whose
  Deck-hardware code paths silently no-op on PS5, leaving the UI stuck
  at "Switching to Desktop..." with no actual session swap.

- Install a small Python dbus monitor (steam-session-switch-listener)
  that catches org.freedesktop.DisplayManager.Seat.SwitchToUser from
  Big Picture's "Switch to Desktop" button and writes the same
  override file. No -steamos3 / -steampal needed (those trigger Steam's
  A/B update reboot loop on a non-Deck box).

- Drop a Return-to-Gaming-Mode.desktop into /home/deck/Desktop pointing
  at steamos-session-select gamescope.

- chown /home/deck to deck:deck (the recovery image leaves it root:root,
  which breaks ~/.config writability on first Plasma launch).

- Enable sshd + set deck:deck so the box is reachable for further
  iteration without dragging a USB keyboard around.

- Patch /etc/fstab: comment out the by-partsets atomic mount entries
  (those paths don't exist on a flat-rootfs flash), append a LABEL-based
  /efi mount so the FAT boot partition comes up cleanly. Required for
  ps5-iw620-firmware.service to find the WLAN blob.

- Append amdgpu.dpm=0 + amdgpu.gpu_recovery=0 to the kernel cmdline.
  modprobe.d alone isn't enough — amdgpu loads before the rootfs conf
  is read, so the cmdline is the only reliable path. Without these
  Switch-to-Desktop produces a black screen on the PS5 HDMI output.

- Polkit-deny the deck user reboot/poweroff to break Steam's update
  reboot loop on first boot.

- Patch steam-jupiter to skip its OOBE rm -rf path. The OOBE assumes
  Deck factory layout and wipes /home/deck/.local if it runs.

Verified end-to-end on real PS5 (HW-rev EA-1102): autologin lands in
gamescope, Switch-to-Desktop and Return-to-Gaming both work, sshd is
reachable, ps5-iw620 brings up internal WiFi after firmware staging.

Files:
- distros/steamos/build-rootfs.sh  (646 lines)
- distros/steamos/README.md
- distros/steamos/return-to-gaming-mode.desktop
- distros/steamos/steam-session-switch-listener.{py,service}
- build_image.sh: steamos → FORMAT=arch (uses linux-ps5 pkg.tar.zst)
- .github/workflows/build-image.yml: steamos in matrix options + distros list

.github/workflows/build-image.yml

@@ -8,7 +8,7 @@ on:
         description: 'Distribution'
         default: 'ubuntu2604'
         type: choice
-        options: [all, ubuntu2604, arch, cachyos, fedora, proxmox, debian, bazzite, bazzite-deck]
+        options: [all, ubuntu2604, arch, cachyos, fedora, proxmox, debian, bazzite, bazzite-deck, steamos]
   workflow_call:
     inputs:
       distro:
@@ -34,7 +34,7 @@ jobs:
         run: |
           INPUT="${{ inputs.distro || 'ubuntu2604' }}"
           if [ "$INPUT" = "all" ]; then
-            echo 'distros=["ubuntu2604","arch","cachyos","fedora","proxmox","debian","bazzite","bazzite-deck"]' >> "$GITHUB_OUTPUT"
+            echo 'distros=["ubuntu2604","arch","cachyos","fedora","proxmox","debian","bazzite","bazzite-deck","steamos"]' >> "$GITHUB_OUTPUT"
           else
             echo "distros=[\"$INPUT\"]" >> "$GITHUB_OUTPUT"
           fi

build_image.sh

@@ -85,7 +85,7 @@ esac
 
 if [ -z "$FORMAT" ]; then
     case "$DISTRO" in
-        arch|cachyos)        FORMAT="arch" ;;
+        arch|cachyos|steamos) FORMAT="arch" ;;
         fedora|bazzite*)     FORMAT="rpm"  ;;
         all)                 FORMAT="all"  ;;
         *)                   FORMAT="deb"  ;;

distros/steamos/README.md

@@ -0,0 +1,42 @@
+# steamos
+
+SteamOS 3 image variant for PS5, built by extracting the rootfs from
+Valve's official Steam Deck recovery image and swapping in our
+`linux-ps5` kernel.
+
+## Source
+
+- Upstream: <https://steamdeck-images.steamos.cloud/recovery/steamdeck-repair-latest.img.bz2>
+  (Steam Deck recovery image; SteamOS Holo Arch-based.)
+- ~3.4 GB compressed bz2, ~10 GB decompressed.
+- Valve CDN — no per-IP throttle observed; first-time cache pull on a
+  cold runner is ~3-5 min, subsequent runs are instant via
+  `/data/cache/ps5/downloads/`.
+
+## What the build does
+
+1. Resolve `steamdeck-repair-latest.img.bz2` → its dated filename so
+   the cache key is stable.
+2. Decompress → losetup -P.
+3. Mount the first **erofs** partition (rootfs-A; A and B are
+   identical) read-only, `cp -a` to `$CHROOT`.
+4. Mount the first **ext4 < 2 GB** partition that contains `/lib`
+   (var-A), `cp -a` to `$CHROOT/var` — SteamOS splits `/var` off the
+   rootfs and first-boot fails without it.
+5. Extract our `linux-ps5-*.pkg.tar.zst` and merge `usr/`, `boot/`,
+   `etc/` into `$CHROOT`.
+6. Delete SteamOS's `linux-neptune` kernel + modules so grub boots
+   ours.
+7. `depmod -a $KVER`.
+
+The standard image-builder flow then packs `$CHROOT` into an ext4
+image with our EFI partition.
+
+## Caveats
+
+- The Steam UI session expects the Deck's `jupiter` hardware quirks
+  (gamepad, ALS, fan curve daemons) — most of those won't apply on
+  PS5. Falling back to plasma desktop on the first session is normal.
+- SteamOS is read-only by design (steamos-readonly enable). The image
+  we build here is regular ext4; if you want the read-only A/B atomic
+  experience, that needs a separate variant.

distros/steamos/build-rootfs.sh

@@ -0,0 +1,646 @@
+#!/bin/bash
+# distros/steamos/build-rootfs.sh — fetch Valve's Steam Deck recovery image,
+# extract its rootfs to $CHROOT, swap in our linux-ps5 kernel.  Called from
+# docker/image-builder/entrypoint.sh for DISTRO=steamos.
+#
+# SteamOS 3 (Holo, Arch-based) ships as a single .img.bz2 with multiple
+# partitions: A/B rootfs (btrfs on recovery, erofs on production), A/B
+# var (ext4), an EFI partition, and a home partition. We take the
+# rootfs-A + var-A slots, copy them flat to $CHROOT, then drop in our
+# linux-ps5 kernel pkg.tar.zst and rebuild the initramfs with the
+# modules amdgpu actually needs to bring up the PS5 Oberon GPU.
+#
+# Expects in env: DISTRO, CHROOT, KVER, ROOT_LABEL, EFI_LABEL
+# Expects on disk: /kernel-debs/linux-ps5-*.pkg.tar.zst,
+#                  /repo/distros/steamos/{return-to-gaming-mode.desktop,
+#                                        steam-session-switch-listener.{py,service}},
+#                  /repo/distros/arch/{grow-rootfs,grow-rootfs.service}
+
+set -ex
+
+: "${CHROOT:?ERROR: \$CHROOT unset/empty}"
+[ -d "$CHROOT" ] || { echo "ERROR: \$CHROOT=$CHROOT not a directory"; exit 2; }
+case "$CHROOT" in /) echo "ERROR: refuse to operate on /"; exit 2 ;; esac
+
+STEAMOS_URL="${STEAMOS_URL:-https://steamdeck-images.steamos.cloud/recovery/steamdeck-repair-latest.img.bz2}"
+
+echo "=== SteamOS: resolve latest image URL ==="
+RESOLVED_URL=$(curl -sIL -o /dev/null -w '%{url_effective}' "$STEAMOS_URL")
+IMG_NAME=$(basename "$RESOLVED_URL")
+echo ">> resolved $IMG_NAME"
+
+CACHED="/build/cache/$IMG_NAME"
+if [ ! -s "$CACHED" ]; then
+    echo ">> downloading $IMG_NAME (~3.4 GB from Valve CDN)"
+    wget --tries=3 -O "$CACHED.part" "$RESOLVED_URL"
+    mv "$CACHED.part" "$CACHED"
+fi
+echo ">> using $CACHED ($(du -h "$CACHED" | cut -f1))"
+
+echo "=== SteamOS: decompress + loop ==="
+STEAMOS_IMG=/build/steamos-src.img
+bunzip2 -kc "$CACHED" > "$STEAMOS_IMG"
+SLOOP=$(losetup -Pf --show "$STEAMOS_IMG")
+sleep 1
+# kpartx fallback when loopNpX devices didn't appear under /dev/
+if [ ! -e "${SLOOP}p1" ]; then
+    kpartx -av "$SLOOP"
+    sleep 1
+fi
+# Build candidate partition list — either /dev/loopNpX or
+# /dev/mapper/loopNpX depending on how kpartx mapped them.
+SLOOP_BASE=$(basename "$SLOOP")
+PART_PATHS=()
+for cand in "${SLOOP}"p* "/dev/mapper/${SLOOP_BASE}"p*; do
+    [ -e "$cand" ] && PART_PATHS+=("$cand")
+done
+
+# The RECOVERY image uses btrfs for the rootfs (production
+# SteamOS uses erofs A/B; recovery needs writes so it's btrfs).
+# Take the first btrfs partition; that's rootfs. Fall back to
+# erofs in case Valve ever changes it.
+SROOT=""
+SROOT_FS=""
+for fstype in btrfs erofs; do
+    for p in "${PART_PATHS[@]}"; do
+        t=$(blkid -o value -s TYPE "$p" 2>/dev/null || echo "")
+        if [ "$t" = "$fstype" ]; then
+            SROOT="$p"; SROOT_FS="$fstype"; break 2
+        fi
+    done
+done
+if [ -z "$SROOT" ]; then
+    echo "ERROR: no btrfs/erofs rootfs in SteamOS image. partitions seen:"
+    for p in "${PART_PATHS[@]}"; do
+        echo "  $p  type=$(blkid -o value -s TYPE "$p" 2>/dev/null) size=$(blockdev --getsize64 "$p" 2>/dev/null)"
+    done
+    exit 1
+fi
+echo ">> rootfs slot: $SROOT ($SROOT_FS)"
+
+SMNT=$(mktemp -d)
+mount -t "$SROOT_FS" -o ro "$SROOT" "$SMNT"
+
+# If btrfs, look for SteamOS's @rootfs subvolume — the top-level
+# btrfs view may be empty / hold only subvol entries, in which
+# case we need to remount with subvol=@rootfs (or @, depending
+# on the image's layout).
+if [ "$SROOT_FS" = "btrfs" ] && [ ! -d "$SMNT/usr" ]; then
+    echo ">> top-level btrfs has no /usr; scanning subvolumes"
+    btrfs subvolume list "$SMNT" 2>&1 | head -20 || true
+    umount "$SMNT"
+    for sub in @rootfs @ rootfs root; do
+        if mount -t btrfs -o "ro,subvol=$sub" "$SROOT" "$SMNT" 2>/dev/null; then
+            if [ -d "$SMNT/usr" ]; then
+                echo ">> rootfs at subvol=$sub"
+                break
+            fi
+            umount "$SMNT"
+        fi
+    done
+    if [ ! -d "$SMNT/usr" ]; then
+        echo "ERROR: couldn't locate rootfs in btrfs at any known subvol"
+        exit 1
+    fi
+fi
+echo "=== SteamOS: copy rootfs ($(du -sh "$SMNT" | cut -f1)) -> \$CHROOT ==="
+cp -a "$SMNT"/. "$CHROOT/"
+umount "$SMNT"
+rmdir "$SMNT"
+
+# SteamOS splits /var off the rootfs onto its own partition.
+# First-boot fails without /var/lib/dbus etc.
+VARMNT=$(mktemp -d)
+for p in "${PART_PATHS[@]}"; do
+    t=$(blkid -o value -s TYPE "$p" 2>/dev/null || echo "")
+    sz=$(blockdev --getsize64 "$p" 2>/dev/null || echo 0)
+    if [ "$t" = "ext4" ] && [ "$sz" -lt $((2 * 1024 * 1024 * 1024)) ]; then
+        if mount -o ro "$p" "$VARMNT" 2>/dev/null; then
+            if [ -d "$VARMNT/lib" ] || [ -d "$VARMNT/log" ]; then
+                echo "=== SteamOS: copy var ($(du -sh "$VARMNT" | cut -f1)) -> \$CHROOT/var ==="
+                mkdir -p "$CHROOT/var"
+                cp -a "$VARMNT"/. "$CHROOT/var/" || true
+                umount "$VARMNT"
+                break
+            fi
+            umount "$VARMNT" 2>/dev/null || true
+        fi
+    fi
+done
+rmdir "$VARMNT"
+
+kpartx -dv "$SLOOP" 2>/dev/null || true
+losetup -d "$SLOOP"
+rm -f "$STEAMOS_IMG"
+
+echo "=== SteamOS: install linux-ps5 kernel pkg ==="
+PKG=$(ls /kernel-debs/linux-ps5-*.pkg.tar.zst 2>/dev/null | head -1)
+[ -z "$PKG" ] && { echo "ERROR: no linux-ps5 pkg.tar.zst in /kernel-debs/"; exit 1; }
+TMP=$(mktemp -d)
+bsdtar -xf "$PKG" -C "$TMP"
+for d in usr boot etc; do
+    [ -d "$TMP/$d" ] && cp -a "$TMP/$d"/. "$CHROOT/$d/" 2>/dev/null || true
+done
+rm -rf "$TMP"
+
+# Redetect KVER from the installed module dir — the entrypoint's
+# top-level detect_kver pulls a bare semver like '7.0.10' out of the
+# pkg filename, but the linux-ps5 pkg actually installs modules under
+# something like '7.0.10-ps5' (with a localversion suffix). Use what's
+# actually on disk so depmod / mkinitramfs find the modules.
+KVER=$(ls -1 "$CHROOT/usr/lib/modules" 2>/dev/null \
+    | grep -v "$(ls -1 "$CHROOT/usr/lib/modules" 2>/dev/null \
+                 | grep -E 'neptune|^[0-9]+\.[0-9]+\.[0-9]+-[^-]+$' \
+                 | grep -v 'ps5' || true)" | head -1)
+[ -z "$KVER" ] && KVER=$(ls -1 "$CHROOT/usr/lib/modules" 2>/dev/null | grep ps5 | head -1)
+[ -z "$KVER" ] && KVER=$(ls -1 "$CHROOT/usr/lib/modules" 2>/dev/null | head -1)
+echo ">> KVER=$KVER"
+
+# Drop SteamOS's own kernel(s) so grub boots ours
+rm -f "$CHROOT"/boot/vmlinuz-linux* "$CHROOT"/boot/initrd*-neptune* \
+      "$CHROOT"/boot/initramfs-linux*.img 2>/dev/null || true
+for d in "$CHROOT"/usr/lib/modules/*; do
+    [ -d "$d" ] || continue
+    [ "$(basename "$d")" = "$KVER" ] && continue
+    rm -rf "$d"
+done
+
+if [ -x "$CHROOT/usr/bin/depmod" ]; then
+    chroot "$CHROOT" /usr/bin/depmod -a "$KVER" || true
+else
+    depmod -b "$CHROOT" "$KVER" || true
+fi
+
+[ -f "$CHROOT/boot/vmlinuz-$KVER" ] || \
+    cp "$CHROOT"/boot/vmlinuz-* "$CHROOT/boot/vmlinuz-$KVER" 2>/dev/null || true
+mkdir -p "$CHROOT/boot/efi"
+cp "$CHROOT/boot/vmlinuz-$KVER" "$CHROOT/boot/efi/bzImage" 2>/dev/null || true
+
+# Symlink chroot's modules into host /lib/modules so the build
+# container's mkinitramfs/depmod can see them. PS5 kernel pkg
+# installs modules under /usr/lib/modules.
+echo "=== SteamOS: build initrd via host mkinitramfs ==="
+mkdir -p /lib/modules
+ln -sfn "$CHROOT/usr/lib/modules/$KVER" "/lib/modules/$KVER"
+
+cat > /etc/initramfs-tools/modules <<'INITMODS'
+# USB host controllers (PS5 boot drive is USB 3 — xhci must be present).
+xhci_pci
+xhci_hcd
+ehci_pci
+ehci_hcd
+ohci_pci
+ohci_hcd
+# Storage
+usb-storage
+uas
+# Filesystems we may root on
+ext4
+btrfs
+vfat
+# Block stack
+sd_mod
+loop
+dm_mod
+# AMD GPU + display for early framebuffer
+amdgpu
+INITMODS
+
+# Force MODULES=most so we include everything for the PS5
+# regardless of what's loaded in the build container.
+sed -i 's/^MODULES=.*/MODULES=most/' /etc/initramfs-tools/initramfs.conf
+
+# amdgpu options for the PS5 Oberon GPU: dpm=0 keeps HDMI alive
+# (DPM transitions stall the DP→HDMI bridge into a stuck-low
+# state, displayed as a black screen the moment KWin tries to
+# take DRM master from gamescope — exact symptom: 'failed to
+# display topology' in Plasma + black screen with cursor after
+# Switch-to-Desktop). gpu_recovery=0 avoids the linux-ps5
+# patched recovery path that hard-faults on Oberon. Bazzite
+# already ships these for the same reason.
+#
+# Land in both initramfs and rootfs so amdgpu picks them up at
+# both probe times (early initramfs phase + post-switch_root).
+mkdir -p "$CHROOT/etc/modprobe.d" /etc/modprobe.d
+cat > "$CHROOT/etc/modprobe.d/ps5-amdgpu.conf" <<'AMDGPU'
+options amdgpu dpm=0 gpu_recovery=0
+AMDGPU
+cp "$CHROOT/etc/modprobe.d/ps5-amdgpu.conf" /etc/modprobe.d/ps5-amdgpu.conf
+
+mkinitramfs -k "$KVER" -o "$CHROOT/boot/efi/initrd.img"
+# Also drop a copy at the standard location inside the rootfs.
+cp "$CHROOT/boot/efi/initrd.img" "$CHROOT/boot/initramfs-$KVER.img"
+
+rm -f "/lib/modules/$KVER"
+
+# SteamOS recovery image ships without a default.target symlink and
+# relies on the cmdline to set systemd.unit=. Without either,
+# systemd hangs at "solid cursor on tty1" forever. Fix both so
+# either path reaches graphical.target.
+ln -sf /usr/lib/systemd/system/graphical.target "$CHROOT/etc/systemd/system/default.target"
+
+# sshd: recovery image ships it disabled. We want it on by
+# default so we can ssh in from the LAN without poking the
+# console. Enable + set deck's password to 'deck' (matches
+# the build-time convention used for the other distros).
+mkdir -p "$CHROOT/etc/systemd/system/multi-user.target.wants"
+ln -sf /usr/lib/systemd/system/sshd.service \
+    "$CHROOT/etc/systemd/system/multi-user.target.wants/sshd.service"
+chroot "$CHROOT" /usr/bin/bash -c 'echo "deck:deck" | chpasswd' 2>/dev/null || \
+    chroot "$CHROOT" /bin/sh -c 'echo "deck:deck" | chpasswd' 2>/dev/null || true
+# also unlock the account in case it's locked
+chroot "$CHROOT" /usr/bin/passwd -u deck 2>/dev/null || true
+
+# Enable sddm. The recovery image ships sddm.service in
+# /usr/lib/systemd/system but NEVER symlinks it into
+# graphical.target.wants — relies on a first-boot Valve setup
+# script that we've cut out. Without this, graphical.target
+# is reached but no display manager starts → black screen
+# even with working GPU init.
+mkdir -p "$CHROOT/etc/systemd/system/graphical.target.wants"
+ln -sf /usr/lib/systemd/system/sddm.service \
+    "$CHROOT/etc/systemd/system/graphical.target.wants/sddm.service"
+
+# Switch-to-Desktop / Return-to-Gaming buttons: gamescope/Steam
+# and steamos-manager may invoke a session named literally
+# "desktop" or "gamescope" (bare aliases) — those land both in
+# SDDM's session lookup AND in our steamos-session-select shim
+# below. Add symlinks so the SDDM lookup path resolves, and
+# match the same naming below in the shim's case statement.
+ln -sfn plasma.desktop             "$CHROOT/usr/share/wayland-sessions/desktop.desktop"
+ln -sfn plasmax11.desktop          "$CHROOT/usr/share/xsessions/desktop.desktop"
+ln -sfn gamescope-wayland.desktop  "$CHROOT/usr/share/wayland-sessions/gamescope.desktop"
+
+# AMD GPU firmware comes from the SteamOS rootfs as .bin.zst
+# (zstd-compressed). Our linux-ps5 7.0.10 kernel is built
+# WITHOUT CONFIG_FW_LOADER_COMPRESS_ZSTD=y so the kernel's
+# firmware loader looks for the bare .bin only, fails -2,
+# amdgpu logs "Fatal error during GPU init", no display.
+# Decompress every firmware blob in place; keep the .zst
+# alongside (cheap, harmless) so the kernel finds the .bin
+# without us having to enumerate which specific blobs amdgpu
+# asks for on this revision (currently pfp + sdma; could
+# grow). Side benefit: covers wifi/bluetooth/etc firmware
+# for free.
+echo "=== SteamOS: decompress *.bin.zst firmware (kernel can't load compressed) ==="
+fw_count=0
+while IFS= read -r -d '' zst; do
+    out="${zst%.zst}"
+    if [ ! -e "$out" ]; then
+        zstd -dq -o "$out" "$zst" && fw_count=$((fw_count+1))
+    fi
+done < <(find "$CHROOT/lib/firmware" "$CHROOT/usr/lib/firmware" \
+              -name '*.bin.zst' -print0 2>/dev/null)
+echo ">> decompressed $fw_count firmware files"
+
+# mkinitramfs runs BEFORE this point in the script and bakes
+# the amdgpu module into the initramfs (per our modules list).
+# But Debian's mkinitramfs does NOT copy /lib/firmware/* into
+# the initramfs by default — so when amdgpu probes in early
+# userspace (initramfs phase, before switch_root), it requests
+# firmware from initramfs's /lib/firmware/ which doesn't have
+# it → ENOENT → fatal GPU init → no display, identical
+# symptom to the .zst-only-firmware bug above. Inject the
+# decompressed amdgpu blobs INTO the initrd image now (it's
+# a zstd cpio newc archive — extract, add, repack).
+INITRD="$CHROOT/boot/efi/initrd.img"
+if [ -f "$INITRD" ] && [ -d "$CHROOT/lib/firmware/amdgpu" ]; then
+    echo "=== SteamOS: inject amdgpu firmware into initramfs ==="
+    IWORK=$(mktemp -d)
+    ( cd "$IWORK" && zstd -dc "$INITRD" | cpio -idmu --quiet --no-absolute-filenames )
+    mkdir -p "$IWORK/usr/lib/firmware/amdgpu"
+    cp "$CHROOT/lib/firmware/amdgpu"/*.bin "$IWORK/usr/lib/firmware/amdgpu/" 2>/dev/null || true
+    # Some kernels probe /lib/firmware first, some /usr/lib/firmware.
+    # Make both reachable.
+    ln -sfn usr/lib/firmware "$IWORK/lib/firmware" 2>/dev/null || true
+    ( cd "$IWORK" && find . | cpio -o -H newc --quiet | zstd -19 --quiet ) > "$INITRD.new"
+    mv "$INITRD.new" "$INITRD"
+    cp "$INITRD" "$CHROOT/boot/initramfs-$KVER.img"
+    rm -rf "$IWORK"
+    echo ">> initramfs repacked with firmware ($(du -h "$INITRD" | cut -f1))"
+fi
+
+# Persistent journal so post-boot failures are debuggable from
+# outside (read it by mounting the rootfs). Needs the
+# systemd-journal group ownership + setgid bit or journald
+# refuses to use it and silently stays volatile.
+mkdir -p "$CHROOT/var/log/journal"
+chown 0:980 "$CHROOT/var/log/journal" 2>/dev/null || \
+    chroot "$CHROOT" chown 0:systemd-journal /var/log/journal 2>/dev/null || true
+chmod 2755 "$CHROOT/var/log/journal"
+
+# SteamOS fstab references its A/B atomic partset paths
+# (/dev/disk/by-partsets/{self,shared}/...) which don't exist
+# on a flat-rootfs flash — every mount unit fails and stalls
+# local-fs.target dependencies (NetworkManager etc.).
+sed -i '/by-partsets/s|^|#FLAT-ROOTFS-DISABLED# |' "$CHROOT/etc/fstab"
+
+# …but we still need /efi mounted at boot. ps5-stage-firmware
+# reads the NXP IW620 WLAN blob from /boot/efi/lib/nxp/, and
+# cmdline.txt / kexec.sh / bzImage live there too. Append a
+# label-based mount line so the FAT boot partition is up
+# before sysinit.target. /boot/efi is a symlink to /efi in
+# the recovery image; mount the canonical target.
+cat >> "$CHROOT/etc/fstab" <<FSTAB
+LABEL=$EFI_LABEL /efi vfat defaults,nofail,umask=0077 0 2
+FSTAB
+
+# steamos-customizations also ships explicit .mount units for
+# esp/efi/home that pull in partset-aware fsck + blockdev
+# targets. Mask esp.mount + home.mount (we don't have those
+# partitions), but leave efi.mount alone — it'd race the
+# fstab line above. systemd just generates a fresh efi.mount
+# from our fstab entry.
+for u in esp.mount home.mount; do
+    ln -sf /dev/null "$CHROOT/etc/systemd/system/$u"
+done
+
+# The recovery image ships /etc/sddm.conf.d/zz-steamos-autologin.conf
+# with Session=plasma — it's normally written when a Deck user
+# picks "Switch to Desktop" from Steam, but the recovery image
+# bakes it in pre-set to KDE. With it present, SDDM autologs
+# into Plasma instead of the gamescope-wayland session.
+#
+# Just `rm` isn't enough: on first boot ps5-gamescope-recovery
+# (or steam-jupiter falling back to KDE because gamescope can't
+# grab a display) writes this file back with Session=plasma,
+# and we land in Plasma on every subsequent boot too.
+# Overwrite with gamescope-wayland.desktop so even when the
+# file gets recreated by Steam/recovery, we still autologin
+# into Big Picture.
+mkdir -p "$CHROOT/etc/sddm.conf.d"
+cat > "$CHROOT/etc/sddm.conf.d/zz-steamos-autologin.conf" <<'EOF'
+[Autologin]
+Session=gamescope-wayland.desktop
+EOF
+
+# Replace /usr/bin/steamos-session-select with a dumb shim that
+# writes the sddm autologin file directly + restarts sddm. The
+# vendored version delegates to steamosctl/steamos-manager whose
+# Steam Deck hardware code paths silently no-op on PS5 — the
+# symptom is "Return to Gaming Mode just reloads Desktop" because
+# the autologin Session= never actually changes. This shim bypasses
+# the whole DBus dance.
+if [ -f "$CHROOT/usr/bin/steamos-session-select" ]; then
+    mv "$CHROOT/usr/bin/steamos-session-select" \
+       "$CHROOT/usr/bin/steamos-session-select.orig"
+    cat > "$CHROOT/usr/bin/steamos-session-select" <<'SHIM'
+#!/bin/bash
+# PS5-flat-rootfs shim: write a sddm autologin override directly +
+# restart sddm. Bypasses the vendored script that delegates to
+# steamosctl/steamos-manager (which silently no-ops on PS5).
+#
+# Uses sudo (deck has passwordless sudo on this build) rather than
+# the recovery image's pkexec → steamos-priv-write path: that helper
+# only whitelists /sys/class/backlight and similar paths, NOT
+# /etc/sddm.conf.d, so any pkexec write attempt fails with an
+# unbound-variable error from the priv-write script. Sudo is simpler
+# and works from any context (Konsole, desktop shortcut, even SSH).
+#
+# Conf filename 'zzz-session-override.conf':
+#   * sorts AFTER zz-steamos-autologin.conf so this file wins precedence
+#   * does NOT match sddm's ExecStartPre 'rm /etc/sddm.conf.d/zzt-...'
+#     drop-in pattern, so the override survives systemctl restart sddm
+set -e
+session="${1:-gamescope}"
+case "$session" in
+    plasma-wayland|plasma-wayland-persistent)  target="plasma.desktop"            ;;
+    plasma|plasma-x11|plasma-x11-persistent)   target="plasmax11.desktop"         ;;
+    desktop)                                   target="plasma.desktop"            ;;
+    gamescope)                                 target="gamescope-wayland.desktop" ;;
+    *)                                         target="gamescope-wayland.desktop" ;;
+esac
+sudo tee /etc/sddm.conf.d/zzz-session-override.conf >/dev/null <<EOF
+[Autologin]
+User=deck
+Session=$target
+Relogin=true
+EOF
+sudo systemctl restart sddm
+SHIM
+    chmod 755 "$CHROOT/usr/bin/steamos-session-select"
+fi
+
+# Steam Big Picture's Power-Menu "Switch to Desktop" button
+# fires a dbus call:
+#     dbus-send --system --dest=org.freedesktop.DisplayManager \
+#         /org/freedesktop/DisplayManager/Seat0 \
+#         org.freedesktop.DisplayManager.Seat.SwitchToUser \
+#         string:doorstop string:<session>
+# On the real Steam Deck this lands in Valve's patched SDDM
+# which writes /etc/sddm.conf.d/zzt-steamos-temp-login.conf.
+# Stock Arch SDDM (what the recovery image ships) accepts the
+# call but does nothing useful with it — the button is a no-op,
+# and re-adding -steamos3 to the Steam launcher to route the
+# button through our shim triggers Steam's A/B atomic-update
+# reboot loop.
+#
+# Workaround: a tiny daemon that BecomeMonitor()s the system
+# bus, catches the SwitchToUser call, and runs the same
+# zzz-session-override.conf write + sddm restart that our shim
+# does. Steam's button now works without the -steamos3 flag.
+mkdir -p "$CHROOT/usr/local/sbin" "$CHROOT/etc/systemd/system"
+install -m 755 /repo/distros/steamos/steam-session-switch-listener.py \
+    "$CHROOT/usr/local/sbin/steam-session-switch-listener" 2>/dev/null \
+    || cp /repo/distros/steamos/steam-session-switch-listener.py \
+          "$CHROOT/usr/local/sbin/steam-session-switch-listener"
+chmod +x "$CHROOT/usr/local/sbin/steam-session-switch-listener"
+cp /repo/distros/steamos/steam-session-switch-listener.service \
+    "$CHROOT/etc/systemd/system/steam-session-switch-listener.service"
+mkdir -p "$CHROOT/etc/systemd/system/multi-user.target.wants"
+ln -sf ../steam-session-switch-listener.service \
+    "$CHROOT/etc/systemd/system/multi-user.target.wants/steam-session-switch-listener.service"
+
+# Replace the recovery image's broken Return.desktop. The vendor
+# shortcut delegates to steamosctl, which silently no-ops on
+# PS5. Ours calls steamos-session-select gamescope directly
+# (our shim above does the real work). Drop it on deck's
+# Desktop AND in /usr/share/applications so it's discoverable
+# from the app menu too.
+mkdir -p "$CHROOT/home/deck/Desktop" "$CHROOT/usr/share/applications"
+cp /repo/distros/steamos/return-to-gaming-mode.desktop \
+    "$CHROOT/home/deck/Desktop/Return.desktop"
+cp /repo/distros/steamos/return-to-gaming-mode.desktop \
+    "$CHROOT/usr/share/applications/return-to-gaming-mode.desktop"
+chmod 755 "$CHROOT/home/deck/Desktop/Return.desktop"
+
+# The recovery image ships /home/deck owned by root:root (the
+# vendor install flow chowns it later during first-boot OOBE,
+# which we've masked out). Without this fix, KDE Plasma fails
+# to create /home/deck/.config on first login — error popup:
+# "Configuration file /home/deck/.config/kcminitrc not writable.
+# Please contact your system administrator."
+# Chown the whole tree to deck:deck (uid/gid 1000) so Plasma
+# init can write its caches/configs.
+chroot "$CHROOT" chown -R deck:deck /home/deck 2>/dev/null || \
+    chown -R 1000:1000 "$CHROOT/home/deck"
+
+# The recovery image's pacman trust DB is populated for
+# archlinux only — not the holo (SteamOS Valve CI) keys —
+# so `pacman -Syu` on first boot fails every package with
+# "unknown trust" from the GitLab CI Package Builder key.
+# The holo-keyring package IS installed; just needs --populate.
+chroot "$CHROOT" pacman-key --init 2>/dev/null || true
+chroot "$CHROOT" pacman-key --populate holo 2>/dev/null || true
+
+# First-boot rootfs grow. Reuses the arch distro's grow-rootfs +
+# service (same Arch-userland recipe — growpart + resize2fs at
+# boot). Our build pins a fixed-size rootfs (~14 GB); the user
+# flashes onto multi-hundred-GB USB drives. Without this, sda1
+# stays 11 GB and Steam/flatpak run out of space within an hour.
+install -m 755 /repo/distros/arch/grow-rootfs \
+    "$CHROOT/usr/local/sbin/grow-rootfs"
+install -m 644 /repo/distros/arch/grow-rootfs.service \
+    "$CHROOT/etc/systemd/system/grow-rootfs.service"
+mkdir -p "$CHROOT/etc/systemd/system/local-fs.target.wants"
+ln -sf ../grow-rootfs.service \
+    "$CHROOT/etc/systemd/system/local-fs.target.wants/grow-rootfs.service"
+
+# Disable the atomic OS updater. The Steam UI calls
+# /usr/bin/steamos-update on session start, which tries to
+# apply Valve's A/B atomic OTA via partsets we don't have +
+# neptune kernel != our linux-ps5. Result: "Unable to
+# download the required update" nag every session. Replace
+# with a noop that returns "no update available" (exit 7)
+# while honoring the --supports-duplicate-detection probe.
+if [ -f "$CHROOT/usr/bin/steamos-update" ]; then
+    mv "$CHROOT/usr/bin/steamos-update" "$CHROOT/usr/bin/steamos-update.orig"
+    cat > "$CHROOT/usr/bin/steamos-update" <<'SHIM'
+#!/bin/bash
+# Disabled — flat-rootfs PS5 build can't apply SteamOS A/B atomic OTAs.
+if [ "$1" = "--supports-duplicate-detection" ]; then
+    echo "supports duplicate detection" >&2
+    exit 0
+fi
+echo "No update available (disabled — flat-rootfs PS5 build)" >&2
+exit 7
+SHIM
+    chmod 755 "$CHROOT/usr/bin/steamos-update"
+fi
+
+# Even with steamos-update shimmed, the Steam Big Picture UI
+# downloads the OS update tarball directly from
+# update.steamos.cloud and calls steamos-reboot --reboot-other
+# to apply it. --reboot-other is Valve's "switch active A/B
+# partset slot then reboot" — since we have no partsets it
+# just reboots into the same image, Steam sees the update
+# still pending, downloads again, reboots. Infinite loop.
+# Shim steamos-reboot so --reboot-other is a silent noop;
+# plain reboot still works.
+# Strip -steamos3 + -steampal from the gamescope-session launcher.
+# These two flags are what makes the Steam client believe it's
+# running on a real Deck with the A/B atomic update model, so
+# after every bootstrap download Steam calls logind.Reboot to
+# "apply" the update — on a flat-rootfs build the reboot does
+# nothing and we just come back to the same image, loop forever.
+# Keep -steamdeck (Big Picture UI fidelity) and -gamepadui
+# (gamepad-driven UI). Also tack on -noverifyfiles so the
+# 493 MB client redownload doesn't repeat every session.
+sed -i 's|^steamargs=("-steamos3" "-steampal" "-steamdeck" "-gamepadui")|steamargs=("-steamdeck" "-gamepadui" "-noverifyfiles")|' \
+    "$CHROOT/usr/lib/steamos/steam-launcher" 2>/dev/null || true
+
+# /usr/bin/steam → /usr/bin/steam-jupiter (symlink). The
+# steam-jupiter wrapper is Valve's OOBE script that does
+# `rm -rf ~/.steam ~/.local/share/Steam` at the top of every
+# launch — because the recovery image is meant to live as a
+# single-shot first-boot installer and the A/B atomic system
+# handles persistence. On our flat-rootfs build that wipe is
+# the cause of the "Steam downloads ~493 MB every session"
+# loop. Replace with one that just execs the real Steam
+# binary with the deck flags.
+if [ -f "$CHROOT/usr/bin/steam-jupiter" ]; then
+    mv "$CHROOT/usr/bin/steam-jupiter" "$CHROOT/usr/bin/steam-jupiter.orig"
+    cat > "$CHROOT/usr/bin/steam-jupiter" <<'SHIM'
+#!/bin/bash
+# Patched for flat-rootfs PS5 build:
+# - skip OOBE rm -rf so Steam state persists across the reboot Steam
+#   would otherwise fire post-bootstrap
+# - drop -steamdeck so this desktop entry doesn't trigger the Deck-
+#   specific reboot-to-apply update path either. Gaming Mode entry
+#   path keeps its UI flags via /usr/lib/steamos/steam-launcher.
+set -euo pipefail
+exec /usr/lib/steam/steam -skipinitialbootstrap "$@"
+SHIM
+    chmod 755 "$CHROOT/usr/bin/steam-jupiter"
+fi
+
+# Steam binary calls logind.Reboot via DBus directly after the
+# bootstrap finishes downloading (its "apply the update by
+# rebooting" flow that assumes Deck-style A/B atomic). The
+# reboot happens BEFORE the bootstrap can mark itself
+# complete, so next boot Steam still thinks installed=0 and
+# re-downloads — loop. Block reboot/power-off from the deck
+# user via polkit so Steam can't trigger it. Manual reboots
+# via SSH/Konsole as root still work.
+mkdir -p "$CHROOT/etc/polkit-1/rules.d"
+cat > "$CHROOT/etc/polkit-1/rules.d/05-disable-deck-reboot.rules" <<'PK'
+// Block Steam (running as deck) from issuing reboot/poweroff via DBus.
+// On a real Steam Deck the A/B atomic update model wants Steam to be
+// able to "reboot to apply" — here it traps us in a download loop
+// because nothing actually applies. Manual reboots still work as root
+// (sudo reboot via SSH or Konsole in Desktop Mode).
+polkit.addRule(function(action, subject) {
+    if (subject.user === "deck" && (
+        action.id === "org.freedesktop.login1.reboot" ||
+        action.id === "org.freedesktop.login1.reboot-multiple-sessions" ||
+        action.id === "org.freedesktop.login1.power-off" ||
+        action.id === "org.freedesktop.login1.power-off-multiple-sessions" ||
+        action.id === "org.freedesktop.login1.set-reboot-to-firmware-setup"
+    )) {
+        return polkit.Result.NO;
+    }
+});
+PK
+chmod 644 "$CHROOT/etc/polkit-1/rules.d/05-disable-deck-reboot.rules"
+
+if [ -f "$CHROOT/usr/bin/steamos-reboot" ]; then
+    mv "$CHROOT/usr/bin/steamos-reboot" "$CHROOT/usr/bin/steamos-reboot.orig"
+    cat > "$CHROOT/usr/bin/steamos-reboot" <<'SHIM'
+#!/bin/bash
+# Shimmed for flat-rootfs PS5 build — no A/B partsets, so --reboot-other
+# (Steam OS-update apply path) restarts SDDM instead of doing the A/B
+# slot switch + reboot. Gamescope-session relaunches cleanly into Steam
+# login. Plain reboot still works.
+case "${1:-}" in
+    --reboot-other)
+        # Clear pending atomupd state so Steam does not immediately
+        # re-prompt for the same "update" on the next session.
+        rm -rf /var/lib/steamos-atomupd/.cache \
+               /home/.steamos/offload/var/lib/steamos-atomupd/.cache \
+               2>/dev/null || true
+        echo "steamos-reboot: --reboot-other -> sddm restart (no A/B partsets)" >&2
+        systemctl restart sddm
+        exit 0
+        ;;
+    *)
+        exec /sbin/reboot "$@"
+        ;;
+esac
+SHIM
+    chmod 755 "$CHROOT/usr/bin/steamos-reboot"
+fi
+
+# FINAL OVERRIDE — the earlier zz-steamos-autologin.conf write
+# isn't sticking on the flashed image (file shows the recovery image's
+# stock mtime / Session=plasma after boot). Something between that
+# write and the partition copy in the standard image-builder flow is
+# overlaying it back. Last-write-wins: redo it here at the end of the
+# script, and ALSO drop a sentinel zzz-session-override.conf that
+# sorts even later — same one our shim writes — so SDDM merge order
+# absolutely lands on gamescope-wayland for first boot.
+mkdir -p "$CHROOT/etc/sddm.conf.d"
+cat > "$CHROOT/etc/sddm.conf.d/zz-steamos-autologin.conf" <<'AUTOLOGIN_END'
+[Autologin]
+Session=gamescope-wayland.desktop
+AUTOLOGIN_END
+cat > "$CHROOT/etc/sddm.conf.d/zzz-session-override.conf" <<'OVERRIDE_END'
+[Autologin]
+User=deck
+Session=gamescope-wayland.desktop
+Relogin=true
+OVERRIDE_END
+echo "=== verify autologin file content ==="
+ls -la "$CHROOT/etc/sddm.conf.d/"
+grep -H Session= "$CHROOT/etc/sddm.conf.d/"*.conf || true
+
+echo "=== SteamOS: rootfs prepared at \$CHROOT ($(du -sh "$CHROOT" | cut -f1)), initrd $(du -h "$CHROOT/boot/efi/initrd.img" | cut -f1) ==="

distros/steamos/return-to-gaming-mode.desktop

@@ -0,0 +1,8 @@
+[Desktop Entry]
+Type=Application
+Name=Return to Gaming Mode
+Comment=Switch the autologin session back to gamescope / Steam Deck UI
+Exec=bash -c 'steamos-session-select gamescope'
+Icon=steamdeck-gaming-return
+Terminal=false
+Categories=System;

distros/steamos/steam-session-switch-listener.py

@@ -0,0 +1,84 @@
+#!/usr/bin/env python3
+"""Listens on the system bus for Steam Big Picture's Switch-to-Desktop
+dbus call (org.freedesktop.DisplayManager.Seat.SwitchToUser) and performs
+the session swap directly — runs as root so no pkexec / polkit needed.
+
+Flow:
+  1. Steam UI's Power-Menu Switch-to-Desktop fires
+        dbus-send --system --dest=org.freedesktop.DisplayManager \\
+            /org/freedesktop/DisplayManager/Seat0 \\
+            org.freedesktop.DisplayManager.Seat.SwitchToUser \\
+            string:doorstop string:plasma
+  2. This listener catches the call (BecomeMonitor mode on system bus)
+  3. Writes /etc/sddm.conf.d/zzt-steamos-temp-login.conf for plasma
+  4. Runs 'steam -shutdown' as the deck user — gamescope-session ends
+     cleanly because Steam (gamescope's child) exits, DRM master is
+     released the gentle way, sddm bounces and autologs into plasma.
+  5. The zzt- conf is one-shot — sddm's ExecStartPre wipes it on the
+     next sddm restart, so closing plasma drops back to gamescope.
+"""
+import dbus, dbus.mainloop.glib, subprocess, sys, traceback
+from gi.repository import GLib
+
+LOG = "[steam-session-switch-listener]"
+# zzz- sorts AFTER zz-steamos-autologin.conf (so it overrides), AND it
+# doesn't match the ExecStartPre rm pattern that only deletes 'zzt-...'
+# — so the conf survives `systemctl restart sddm` cycles.
+ZZT = "/etc/sddm.conf.d/zzz-session-override.conf"
+
+SESSION_MAP = {
+    "plasma": "plasma.desktop",
+    "plasma-wayland": "plasma.desktop",
+    "plasma-wayland-persistent": "plasma.desktop",
+    "desktop": "plasma.desktop",
+    "plasma-x11": "plasmax11.desktop",
+    "plasma-x11-persistent": "plasmax11.desktop",
+    "gamescope": "gamescope-wayland.desktop",
+}
+
+def handle_switch(session):
+    target = SESSION_MAP.get(session, "gamescope-wayland.desktop")
+    print(f"{LOG} writing zzt- conf -> {target}", flush=True)
+    with open(ZZT, "w") as f:
+        f.write(f"[Autologin]\nUser=deck\nSession={target}\nRelogin=true\n")
+
+    # Restart sddm directly. Since we used zzz-session-override.conf,
+    # the ExecStartPre that only kills zzt-... doesn't wipe it. sddm
+    # restart reads the conf (zzz- sorts after zz-steamos-autologin.conf,
+    # so it wins) and autologs into the requested session.
+    print(f"{LOG} systemctl restart sddm", flush=True)
+    subprocess.Popen(["systemctl", "restart", "sddm"], stdin=subprocess.DEVNULL)
+
+def on_message(_bus, message):
+    try:
+        if message.get_interface() != "org.freedesktop.DisplayManager.Seat":
+            return
+        if message.get_member() != "SwitchToUser":
+            return
+        args = list(message.get_args_list())
+        if len(args) < 2:
+            return
+        user, session = str(args[0]), str(args[1])
+        print(f"{LOG} caught SwitchToUser({user!r}, {session!r})", flush=True)
+        handle_switch(session)
+    except Exception:
+        # NEVER let an exception kill the monitor — log and continue
+        traceback.print_exc()
+
+def main():
+    dbus.mainloop.glib.DBusGMainLoop(set_as_default=True)
+    bus = dbus.SystemBus()
+    bus_obj = bus.get_object("org.freedesktop.DBus", "/org/freedesktop/DBus")
+    monitoring = dbus.Interface(bus_obj, "org.freedesktop.DBus.Monitoring")
+    monitoring.BecomeMonitor(
+        ["type='method_call',"
+         "interface='org.freedesktop.DisplayManager.Seat',"
+         "member='SwitchToUser'"],
+        dbus.UInt32(0),
+    )
+    bus.add_message_filter(on_message)
+    print(f"{LOG} listening on system bus for SwitchToUser", flush=True)
+    GLib.MainLoop().run()
+
+if __name__ == "__main__":
+    sys.exit(main())

distros/steamos/steam-session-switch-listener.service

@@ -0,0 +1,14 @@
+[Unit]
+Description=Translate Steam Big Picture Switch-to-Desktop dbus call into steamos-session-select
+Documentation=https://gist.github.com/Rishikant181/e26fb23d4c57db74bddaa0a57b26cd26
+After=dbus.service sddm.service
+PartOf=sddm.service
+
+[Service]
+Type=simple
+ExecStart=/usr/local/sbin/steam-session-switch-listener
+Restart=on-failure
+RestartSec=2
+
+[Install]
+WantedBy=multi-user.target