fix(client-linux): Deck Gaming Mode — auto pad type, real chrome-less fullscreen, leave-to-Gaming-Mode, colour bisect

- "Automatic" gamepad type resolves to the virtual Steam Deck pad on Deck
  hardware (env SteamDeck / DMI Jupiter|Galileo): the built-in 28DE:1205
  identity is invisible at Hello time — the Valve HIDAPI drivers run
  in-session only and Steam Input shadows the pad with its virtual X360 —
  so auto always fell through to Xbox 360. "steamdeck" is now also
  selectable in Settings.
- Chrome-less launches flatten the window CSS (border-radius/box-shadow)
  and fullscreen at startup: gamescope never ACKs the xdg fullscreen
  state, so adwaita kept the floating-CSD rounded corners + shadow
  visible over the stream.
- Gaming-Mode --connect launches quit on session end, so Steam ends the
  "game" and the Deck returns to Gaming Mode — previously the app popped
  to its own hosts page, stranding the user fullscreen and making the
  escape chord read as broken.
- The capture hint is controller-aware; the chromeless hint teaches the
  hold-chord ("hold L1+R1+Start+Select to leave") and a quick chord press
  re-flashes it.
- Colour bisect for the reported off-colours on the VAAPI dmabuf path:
  graphics offload defaults OFF under gamescope (a subsurface hands the
  NV12 CSC to the compositor), PUNKTFUNK_OFFLOAD=1|0 overrides, and each
  colour-signaling change logs whether GDK accepted the BT.709-narrow
  color state (fallback = GDK's BT.601 dmabuf default).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

clients/linux/src/app.rs

@@ -30,6 +30,10 @@ const CSS: &str = "
 .pf-poster { border-radius: 10px; background: alpha(currentColor, 0.08); }
 .pf-poster-monogram { font-size: 2.4em; font-weight: bold; color: alpha(currentColor, 0.45); }
 .pf-store-badge { color: white; background: rgba(0, 0, 0, 0.55); }
+/* Gaming-Mode launches: gamescope displays the window fullscreen but never ACKs the
+   xdg_toplevel fullscreen state, so GTK keeps the floating-CSD styling — libadwaita's
+   rounded corners + shadow margin stay visible over the stream. Flatten them outright. */
+window.pf-chromeless { border-radius: 0; box-shadow: none; }
 ";
 
 pub struct App {
@@ -44,6 +48,10 @@ pub struct App {
     pub busy: std::cell::Cell<bool>,
     /// Steam Deck / Gaming-Mode launch: fullscreen the window (chrome-less) when a stream starts.
     pub fullscreen: bool,
+    /// Quit when the session ends (Gaming-Mode `--connect` launch): the app IS the stream —
+    /// exiting ends the Steam "game" so the Deck returns to Gaming Mode instead of stranding
+    /// the user on the client's own hosts page.
+    pub quit_on_session_end: bool,
     /// The hosts page handle (banner + per-card connecting spinner), set right after the
     /// page is built — `None` only during construction.
     pub hosts: RefCell<Option<Rc<HostsUi>>>,
@@ -116,6 +124,14 @@ fn build_ui(gtk_app: &adw::Application) {
         .content(&toasts)
         .build();
 
+    let fullscreen = crate::cli::fullscreen_mode();
+    if fullscreen {
+        // Chrome-less shell: no CSD rounding/shadow (see CSS — gamescope never ACKs the
+        // fullscreen state, so GTK would keep them), and ask for fullscreen up front.
+        window.add_css_class("pf-chromeless");
+        window.fullscreen();
+    }
+
     let app = Rc::new(App {
         window: window.clone(),
         nav: nav.clone(),
@@ -124,7 +140,8 @@ fn build_ui(gtk_app: &adw::Application) {
         identity,
         gamepad: crate::gamepad::GamepadService::start(),
         busy: std::cell::Cell::new(false),
-        fullscreen: crate::cli::fullscreen_mode(),
+        fullscreen,
+        quit_on_session_end: fullscreen && crate::cli::cli_connect_request().is_some(),
         hosts: RefCell::new(None),
     });
 

clients/linux/src/gamepad.rs

@@ -114,6 +114,21 @@ fn pref_for_type(t: sdl3::gamepad::GamepadType) -> GamepadPref {
     }
 }
 
+/// Best-effort "this machine is a Steam Deck". The Gaming-Mode env short-circuits; desktop
+/// mode falls back to DMI (Valve board, Jupiter = LCD / Galileo = OLED — readable inside the
+/// flatpak sandbox). Cached: the answer can't change while we run.
+pub fn is_steam_deck() -> bool {
+    static DECK: std::sync::OnceLock<bool> = std::sync::OnceLock::new();
+    *DECK.get_or_init(|| {
+        if std::env::var_os("SteamDeck").is_some() {
+            return true;
+        }
+        let dmi = |f: &str| std::fs::read_to_string(format!("/sys/class/dmi/id/{f}"));
+        dmi("board_vendor").is_ok_and(|v| v.trim() == "Valve")
+            && dmi("product_name").is_ok_and(|p| matches!(p.trim(), "Jupiter" | "Galileo"))
+    })
+}
+
 enum Ctl {
     Attach(Arc<NativeClient>),
     Detach,
@@ -197,8 +212,19 @@ impl GamepadService {
 
     /// What "Automatic" resolves to right now — the virtual pad matching the physical one
     /// (Swift parity); no pad connected leaves the host's own default.
+    ///
+    /// **Steam Deck special case:** this is read at session start, *before* attach — but the
+    /// Deck's built-in controller is only enumerable with its real 28DE:1205 identity while
+    /// the Valve HIDAPI drivers run, and those are enabled on attach only (see
+    /// [`set_valve_hidapi`]); with Steam Input on, SDL sees nothing but Steam's virtual
+    /// X360 pad anyway. Both cases used to fall through to Xbox 360. On a Deck, a virtual
+    /// pad (or no pad at all) means the physical controller behind it IS the built-in one —
+    /// resolve to the Steam Deck virtual pad so the paddles/trackpads/gyro have somewhere
+    /// to land. A real external controller still wins (it's the one that gets forwarded).
     pub fn auto_pref(&self) -> GamepadPref {
         match self.active() {
+            Some(p) if !p.steam_virtual => p.pref,
+            _ if is_steam_deck() => GamepadPref::SteamDeck,
             Some(p) => p.pref,
             None => GamepadPref::Auto,
         }

clients/linux/src/launch.rs

@@ -266,6 +266,9 @@ impl SessionUi {
             inhibit_shortcuts: self.inhibit,
             show_stats: self.show_stats,
             chromeless: self.app.fullscreen,
+            // The attach just went out, so a Deck's built-in pad may not have enumerated
+            // yet — chromeless (controller-first) shows the chord hint regardless.
+            pad_connected: self.app.gamepad.active().is_some(),
             title,
         });
         self.app.nav.push(&p.page);
@@ -311,6 +314,16 @@ impl SessionUi {
     fn on_ended(&mut self, err: Option<String>) {
         self.close_waiting();
         self.app.gamepad.detach();
+        // Gaming-Mode `--connect` launch: the app IS the stream. Quit so Steam ends the
+        // "game" and the Deck returns to Gaming Mode — popping to our own hosts page would
+        // strand the user in a fullscreen shell with no way back.
+        if self.app.quit_on_session_end {
+            if let Some(e) = err {
+                tracing::warn!(error = %e, "session ended");
+            }
+            self.app.window.close();
+            return;
+        }
         self.app.nav.pop_to_tag("hosts");
         if let Some(h) = self.app.hosts_ui() {
             h.set_connecting(None);

clients/linux/src/ui_settings.rs

@@ -16,7 +16,14 @@ const RESOLUTIONS: &[(u32, u32)] = &[
 ];
 /// `0` = the monitor's native refresh, resolved at connect.
 const REFRESH: &[u32] = &[0, 30, 60, 90, 120, 144, 165, 240];
-const GAMEPADS: &[&str] = &["auto", "xbox360", "dualsense", "xboxone", "dualshock4"];
+const GAMEPADS: &[&str] = &[
+    "auto",
+    "xbox360",
+    "dualsense",
+    "xboxone",
+    "dualshock4",
+    "steamdeck",
+];
 const COMPOSITORS: &[&str] = &["auto", "kwin", "wlroots", "mutter", "gamescope"];
 /// Codec setting values (persisted) paired with their display labels below.
 const CODECS: &[&str] = &["auto", "hevc", "h264", "av1"];
@@ -403,6 +410,7 @@ pub fn show(
             "DualSense",
             "Xbox One",
             "DualShock 4",
+            "Steam Deck",
         ],
     );
     let inhibit_row = adw::SwitchRow::builder()

clients/linux/src/ui_stream.rs

@@ -84,6 +84,9 @@ pub struct StreamPageArgs {
     /// reveal-on-notify chrome hiding) may never fire — the title bar would stay drawn
     /// over the stream. Chrome-less by construction cannot regress that way.
     pub chromeless: bool,
+    /// A controller is connected right now — the capture hint mentions the escape chord.
+    /// (Chromeless implies a controller-first device, so the chord shows there regardless.)
+    pub pad_connected: bool,
     pub title: String,
 }
 
@@ -197,9 +200,10 @@ pub fn new(args: StreamPageArgs) -> StreamPage {
         inhibit_shortcuts,
         show_stats,
         chromeless,
+        pad_connected,
         title,
     } = args;
-    let w = build_widgets(&window, &title, chromeless);
+    let w = build_widgets(&window, &title, chromeless, pad_connected);
     w.stats_label.set_visible(show_stats);
 
     let capture = Rc::new(Capture {
@@ -230,7 +234,7 @@ pub fn new(args: StreamPageArgs) -> StreamPage {
         attach_edge_reveal(&w.toolbar, &w.overlay, &window, &capture);
     }
     let active_handler = attach_capture_lifecycle(&w.overlay, &window, &capture);
-    let escape_future = spawn_escape_watch(&window, &capture, escape_rx);
+    let escape_future = spawn_escape_watch(&window, &capture, escape_rx, &w.fs_hint, chromeless);
     let disconnect_future = spawn_disconnect_watch(&window, &capture, &stop, disconnect_rx);
     wire_teardown(
         &w.page,
@@ -254,6 +258,9 @@ struct PageWidgets {
     picture: gtk::Picture,
     stats_label: gtk::Label,
     hint: gtk::Label,
+    /// The transient chord/fullscreen-exit hint — the escape watch re-flashes it in
+    /// chromeless mode.
+    fs_hint: gtk::Label,
     overlay: gtk::Overlay,
     toolbar: adw::ToolbarView,
     page: adw::NavigationPage,
@@ -264,7 +271,12 @@ struct PageWidgets {
 /// The offloaded picture under an overlay (stats HUD, capture hint, fullscreen hint), a
 /// header bar with the fullscreen toggle, and the window's fullscreen behavior.
 /// `chromeless` (Gaming Mode) builds NO header bar at all — see `StreamPageArgs`.
-fn build_widgets(window: &adw::ApplicationWindow, title: &str, chromeless: bool) -> PageWidgets {
+fn build_widgets(
+    window: &adw::ApplicationWindow,
+    title: &str,
+    chromeless: bool,
+    pad_connected: bool,
+) -> PageWidgets {
     let picture = gtk::Picture::new();
     picture.set_content_fit(gtk::ContentFit::Contain);
 
@@ -273,6 +285,22 @@ fn build_widgets(window: &adw::ApplicationWindow, title: &str, chromeless: bool)
     // no-op wrapper. Black letterboxing keeps fullscreen scanout-eligible.
     let offload = gtk::GraphicsOffload::new(Some(&picture));
     offload.set_black_background(true);
+    // Whether the raw video dmabuf may be handed to the compositor as a subsurface.
+    // Under gamescope (chromeless) default OFF: a subsurface makes the COMPOSITOR do the
+    // NV12→RGB conversion, and gamescope's matrix/range choice for it is outside our
+    // control (off-colours reported on the Deck) — GTK compositing it itself applies the
+    // stream's own BT.709-narrow color state. `PUNKTFUNK_OFFLOAD=1|0` overrides either
+    // way, which also makes the colour question bisectable in one run: offload-off heals →
+    // compositor conversion; still off → GTK/Mesa import (then try PUNKTFUNK_DECODER=software).
+    let offload_on = match std::env::var("PUNKTFUNK_OFFLOAD").ok().as_deref() {
+        Some("0") => false,
+        Some(_) => true,
+        None => !chromeless,
+    };
+    if !offload_on {
+        offload.set_enabled(gtk::GraphicsOffloadEnabled::Disabled);
+        tracing::info!("graphics offload disabled — GTK composites the video itself");
+    }
 
     let stats_label = gtk::Label::new(None);
     stats_label.add_css_class("osd");
@@ -282,9 +310,16 @@ fn build_widgets(window: &adw::ApplicationWindow, title: &str, chromeless: bool)
     stats_label.set_margin_start(12);
     stats_label.set_margin_top(12);
 
-    let hint = gtk::Label::new(Some(
+    // The capture hint speaks the input devices actually present: on a controller-first
-        "Click the stream to capture input · Ctrl+Alt+Shift+Q releases · Ctrl+Alt+Shift+D disconnects · Ctrl+Alt+Shift+S stats",
+    // device (chromeless) or with a pad connected it must surface the chord — keyboard-only
-    ));
+    // text on a Deck told the user nothing they could press.
+    let hint = gtk::Label::new(Some(if chromeless {
+        "Tap the stream to capture input · hold L1 + R1 + Start + Select to leave"
+    } else if pad_connected {
+        "Click the stream to capture input · Ctrl+Alt+Shift+Q releases · Ctrl+Alt+Shift+D disconnects · hold L1 + R1 + Start + Select to leave"
+    } else {
+        "Click the stream to capture input · Ctrl+Alt+Shift+Q releases · Ctrl+Alt+Shift+D disconnects · Ctrl+Alt+Shift+S stats"
+    }));
     hint.add_css_class("osd");
     hint.set_halign(gtk::Align::Center);
     hint.set_valign(gtk::Align::End);
@@ -296,7 +331,7 @@ fn build_widgets(window: &adw::ApplicationWindow, title: &str, chromeless: bool)
     // devices; the L1+R1+Start+Select chord on a controller). Gaming Mode has no F11,
     // no header to reveal, and Steam owns window management — only the chord applies.
     let fs_hint = gtk::Label::new(Some(if chromeless {
-        "L1 + R1 + Start + Select  —  leave the stream (hold to disconnect)"
+        "Hold L1 + R1 + Start + Select  —  leave the stream"
     } else {
         "F11  ·  mouse to the top edge  ·  L1 + R1 + Start + Select  —  exit fullscreen (hold to disconnect)"
     }));
@@ -372,6 +407,7 @@ fn build_widgets(window: &adw::ApplicationWindow, title: &str, chromeless: bool)
         picture,
         stats_label,
         hint,
+        fs_hint,
         overlay,
         toolbar,
         page,
@@ -461,11 +497,15 @@ impl ColorStateCache {
             });
         }
         let state = cicp.build_color_state().ok();
-        if state.is_none() {
+        // One line per signaling change — the on-glass colour bisect reads this to tell
-            tracing::warn!(
+        // "state applied" from "GDK fell back to its YUV default (BT.601)".
+        match &state {
+            Some(_) => tracing::info!(?desc, rgb, "colour signaling → GDK color state"),
+            None => tracing::warn!(
                 ?desc,
-                "GDK can't represent this colour signaling — using default"
+                rgb,
-            );
+                "GDK can't represent this colour signaling — using default (YUV: BT.601)"
+            ),
         }
         self.0 = Some((desc, state.clone()));
         state
@@ -772,20 +812,30 @@ fn attach_capture_lifecycle(
 
 /// Controller escape chord (gamepad service) → leave fullscreen + release capture. The
 /// chord is the only fullscreen exit a controller has (no F11 key; fullscreen hides the
-/// chrome). Aborted on page-hidden so a stale future can't act on the shared window.
+/// chrome). In chromeless mode there is nothing visible to release INTO — a quick press
+/// re-flashes the hold-to-leave hint instead, so an experimenting user learns the hold.
+/// Aborted on page-hidden so a stale future can't act on the shared window.
 fn spawn_escape_watch(
     window: &adw::ApplicationWindow,
     capture: &Rc<Capture>,
     escape_rx: async_channel::Receiver<()>,
+    fs_hint: &gtk::Label,
+    chromeless: bool,
 ) -> glib::JoinHandle<()> {
     let window = window.clone();
     let cap = capture.clone();
+    let fs_hint = fs_hint.clone();
     glib::spawn_future_local(async move {
         while escape_rx.recv().await.is_ok() {
             if window.is_fullscreen() {
                 window.unfullscreen();
             }
             cap.release();
+            if chromeless {
+                fs_hint.set_visible(true);
+                let fs_hint = fs_hint.clone();
+                glib::timeout_add_seconds_local_once(4, move || fs_hint.set_visible(false));
+            }
         }
     })
 }