fix(steamdeck/install): prompt for sudo instead of requiring passwordless

The system-tuning block (UDP buffers, gamepad udev rule, vhci-hcd autoload,
input group) was gated on `sudo -n true` — passwordless sudo — so on a stock
SteamOS box (the deck account needs a password) the whole block was silently
skipped: /dev/uhid stayed root-only so the gamepad degraded to an Xbox 360 pad,
and the UDP buffers stayed at the 416 KB default. Video was unaffected because
Game Mode/gamescope needs none of it, which masked the skip on-glass.

- install.sh + update.sh: acquire sudo interactively (`sudo -v` prompt on a TTY)
  instead of requiring passwordless; skip only when there's no TTY or auth fails,
  and then print the exact manual block plus a `passwd` hint — a stock SteamOS
  'deck' account has no password, so sudo can't work until one is set.
- update.sh: also retrofit the UDP-buffer sysctl for older/skipped installs, and
  loudly nag to reboot when the input group was just added (a --user restart does
  not pick up the new group; only a fresh login does).
- steamos-host.md: note this step prompts for the sudo password.

Root is unavoidable: the udev rule, input group, and vhci-hcd module are all
kernel operations with no user-space alternative.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs-site/content/docs/steamos-host.md

@@ -60,8 +60,8 @@ It is idempotent — safe to re-run. In one pass it:
 3. writes config to `~/.config/punktfunk/` (a generated web-console login password),
 4. raises the UDP socket buffers to 32 MB, installs the gamepad udev rule + the `vhci-hcd` autoload
    and adds you to the `input` group (virtual gamepads / **native Steam Deck controller passthrough**),
-   and seeds the KDE RemoteDesktop grant for Desktop-mode input (needs `sudo`; skipped with a warning
-   if unavailable),
+   and seeds the KDE RemoteDesktop grant for Desktop-mode input — this step **prompts for your `sudo`
+   password** (a stock Steam Deck requires one; without it gamepad passthrough and the UDP tuning are skipped),
 5. installs + starts the `punktfunk-host` and `punktfunk-web` **systemd user services** (with linger,
    so they run without a login session).
 

scripts/steamdeck/install.sh

@@ -189,9 +189,19 @@ else
     [ "$WITH_WEB" = 1 ] && ok "web.env exists (login password unchanged)"
 fi
 
-# --- 4. system tuning (needs sudo; skipped gracefully if unavailable) ------
+# --- 4. system tuning (needs sudo: UDP buffers + gamepad udev rule + vhci-hcd + input group) --------
 log "System tuning (UDP buffers + gamepad rules + vhci-hcd + input group) — needs sudo"
+# Acquire sudo. A stock Steam Deck requires a sudo PASSWORD, so `sudo -n` (non-interactive) fails —
+# we must PROMPT on a TTY, not silently skip. Skipping here is exactly what leaves gamepad passthrough
+# dead (no udev rule / input group / vhci-hcd) and streaming lossy (stock 416 KB UDP buffers).
+SUDO_OK=0
 if sudo -n true 2>/dev/null; then
+    SUDO_OK=1
+elif [ -t 0 ]; then
+    warn "sudo needs your password to set up the gamepad udev rule, vhci-hcd, the input group, and UDP buffers:"
+    sudo -v && SUDO_OK=1 || true
+fi
+if [ "$SUDO_OK" = 1 ]; then
     printf 'net.core.wmem_max=33554432\nnet.core.rmem_max=33554432\n' \
         | sudo tee /etc/sysctl.d/99-punktfunk-net.conf >/dev/null
     sudo sysctl -q -p /etc/sysctl.d/99-punktfunk-net.conf >/dev/null
@@ -217,9 +227,16 @@ if sudo -n true 2>/dev/null; then
         warn "added $USER to the 'input' group (applies on next login)"
     fi
 else
-    warn "passwordless sudo unavailable — skipping UDP-buffer + udev tuning."
-    warn "Without it, high-bitrate streaming drops packets. Apply manually later:"
-    warn "  echo -e 'net.core.wmem_max=33554432\\nnet.core.rmem_max=33554432' | sudo tee /etc/sysctl.d/99-punktfunk-net.conf && sudo sysctl --system"
+    warn "no usable sudo — SKIPPED system tuning. Gamepad passthrough + clean streaming need root (udev"
+    warn "rule, 'input' group, vhci-hcd, UDP buffers) — there is no user-space way to do these."
+    warn "A stock SteamOS 'deck' account has NO password, so sudo can't work until you set one:"
+    warn "  passwd            # set a sudo password once, then re-run this script"
+    warn "Or apply it by hand (then reboot):"
+    warn "  sudo install -m644 $SRC/scripts/60-punktfunk.rules /etc/udev/rules.d/ &&"
+    warn "  sudo install -m644 $SRC/scripts/punktfunk-modules.conf /etc/modules-load.d/punktfunk.conf &&"
+    warn "  sudo usermod -aG input $USER &&"
+    warn "  printf 'net.core.wmem_max=33554432\\nnet.core.rmem_max=33554432\\n' | sudo tee /etc/sysctl.d/99-punktfunk-net.conf &&"
+    warn "  sudo sysctl --system && sudo udevadm control --reload-rules && sudo udevadm trigger"
 fi
 
 # --- 5. systemd user services ---------------------------------------------

scripts/steamdeck/update.sh

@@ -44,24 +44,47 @@ sed "s|^Exec=.*|Exec=$TARGET_DIR/release/punktfunk-host|" "$SRC/packaging/linux/
     > "$HOME/.local/share/applications/io.unom.Punktfunk.Host.desktop"
 ok "KWin desktop-capture authorization refreshed"
 
-# Retrofit the system bits install.sh now sets up but older installs predate (idempotent; the sudo
-# parts are skipped if passwordless sudo isn't available). vhci-hcd = usbip transport for the native
-# Steam Deck pad; 60-punktfunk.rules = /dev/uhid + vhci access; input group = uhid write; the
-# kde-authorized grant (per-user, no root) = Desktop-mode input. A newly-added input group still needs
-# a re-login to apply.
+# Retrofit the system bits install.sh now sets up but older installs predate (idempotent). vhci-hcd =
+# usbip transport for the native Steam Deck pad; 60-punktfunk.rules = /dev/uhid + vhci access; input
+# group = uhid write; the kde-authorized grant (per-user, no root) = Desktop-mode input. A stock Deck
+# needs a sudo PASSWORD, so PROMPT for it rather than silently skipping (skipping = gamepads stay dead).
+SUDO_OK=0
 if sudo -n true 2>/dev/null; then
+    SUDO_OK=1
+elif [ -t 0 ]; then
+    warn "sudo needs your password to (re)apply the gamepad udev rule, vhci-hcd, input group, and UDP buffers:"
+    sudo -v && SUDO_OK=1 || true
+fi
+if [ "$SUDO_OK" = 1 ]; then
     if [ -f "$SRC/scripts/60-punktfunk.rules" ]; then
         sudo install -m644 "$SRC/scripts/60-punktfunk.rules" /etc/udev/rules.d/60-punktfunk.rules
         sudo udevadm control --reload-rules >/dev/null 2>&1 || true
         sudo udevadm trigger >/dev/null 2>&1 || true
+        ok "gamepad udev rule ensured"
     fi
     if [ -f "$SRC/scripts/punktfunk-modules.conf" ]; then
         sudo install -m644 "$SRC/scripts/punktfunk-modules.conf" /etc/modules-load.d/punktfunk.conf
         sudo modprobe vhci-hcd 2>/dev/null || true
         ok "vhci-hcd autoload ensured (native Steam Deck controller)"
     fi
-    id -nG "$USER" | grep -qw input || { sudo usermod -aG input "$USER"; ok "added $USER to 'input' group — log out/in for it to apply"; }
+    # UDP buffers: older installs (or sudo-skipped ones) still run the stock 416 KB cap.
+    if [ ! -f /etc/sysctl.d/99-punktfunk-net.conf ]; then
+        printf 'net.core.wmem_max=33554432\nnet.core.rmem_max=33554432\n' | sudo tee /etc/sysctl.d/99-punktfunk-net.conf >/dev/null
+        sudo sysctl -q -p /etc/sysctl.d/99-punktfunk-net.conf >/dev/null 2>&1 || true
+        ok "UDP socket buffers raised to 32 MB (persisted)"
+    fi
+    if id -nG "$USER" | grep -qw input; then :; else
+        sudo usermod -aG input "$USER"
+        warn "added $USER to the 'input' group — REBOOT (or log out/in) for it to apply"
+    fi
+else
+    warn "no usable sudo — SKIPPED gamepad/udev/vhci/UDP tuning (all root-only; no user-space alternative)."
+    warn "A stock SteamOS 'deck' account has NO password — set one with 'passwd', then re-run. Gamepads stay"
+    warn "Xbox-360 until this runs and you reboot."
 fi
+echo
+warn "If the controller still shows as an Xbox 360 pad, REBOOT the Deck once — the 'input' group and the"
+warn "vhci-hcd module only become live for the host service on a fresh login."
 GRANT_SRC="$SRC/scripts/headless/kde-authorized"
 GRANT_DST="$HOME/.local/share/flatpak/db/kde-authorized"
 if [ ! -s "$GRANT_DST" ] && [ -s "$GRANT_SRC" ]; then