diff --git a/clients/linux/src/launch.rs b/clients/linux/src/launch.rs
index cb4d8cf..d9019ea 100644
--- a/clients/linux/src/launch.rs
+++ b/clients/linux/src/launch.rs
@@ -280,6 +280,35 @@ impl SessionUi {
         if self.app.fullscreen || self.app.settings.borrow().fullscreen_on_stream {
             self.app.window.fullscreen();
         }
+        // Steam Input owning the Deck's built-in controller is invisible degradation: SDL
+        // then sees only Steam's virtual X360 pad, so the right trackpad arrives at the
+        // host as a plain right stick (Steam's default template) and the left trackpad,
+        // paddles and gyro not at all. The real 28DE:1205 identity enumerates shortly
+        // after attach (the Valve HIDAPI drivers are session-scoped) — check once that
+        // settles and say so, instead of streaming silently degraded.
+        if crate::gamepad::is_steam_deck() {
+            let app = self.app.clone();
+            let stop = self.stop.clone();
+            glib::timeout_add_seconds_local_once(4, move || {
+                if stop.load(std::sync::atomic::Ordering::Relaxed) {
+                    return; // session already over
+                }
+                if app.gamepad.active().is_none_or(|pad| pad.steam_virtual) {
+                    tracing::warn!(
+                        "Steam Input is holding the built-in controller — trackpads, \
+                         paddles and gyro won't reach the host (right pad degrades to a \
+                         right stick). Disable Steam Input for Punktfunk to fix this."
+                    );
+                    let toast = adw::Toast::new(
+                        "Steam Input is holding the Deck's controls — trackpads, paddles \
+                         and gyro won't reach the game. Fix: Punktfunk → controller \
+                         settings → Disable Steam Input.",
+                    );
+                    toast.set_timeout(12);
+                    app.toasts.add_toast(toast);
+                }
+            });
+        }
         self.page = Some(p);
     }
 
diff --git a/clients/linux/src/video.rs b/clients/linux/src/video.rs
index fff9b69..0c8beb1 100644
--- a/clients/linux/src/video.rs
+++ b/clients/linux/src/video.rs
@@ -187,6 +187,25 @@ impl Decoder {
             .ok()
             .filter(|v| !v.is_empty())
             .unwrap_or_else(|| pref.to_string());
+        // The Steam Deck's VAAPI zero-copy path renders corrupt/gray/washed-out — validated live;
+        // software decode is clean, correct-colour, and the Deck's APU handles 1280×800 HEVC
+        // easily. Likely cause: since Mesa 25.1 radeonsi exports VCN decode surfaces TILED (with
+        // AMD modifiers) instead of linear, and inside the Flatpak both the VAAPI driver and GTK's
+        // GL come from the runtime's Mesa 26.x — GTK's tiled-NV12 dmabuf import mishandles the new
+        // layout (desktop AMD/Intel boxes validated Tier-1 ran distro Mesa with linear export).
+        // So `auto` resolves to software on a Deck; an explicit `vaapi` (Settings or
+        // PUNKTFUNK_DECODER=vaapi) still forces the hw path for testing — the first-frame
+        // descriptor dump logs the modifier (LINEAR = 0x0), and GSK_RENDERER=ngl|vulkan bisects
+        // the import side.
+        let choice = if (choice == "auto" || choice.is_empty()) && crate::gamepad::is_steam_deck() {
+            tracing::info!(
+                "Steam Deck — defaulting to software decode (AMD VAAPI dmabuf is broken on this \
+                 SteamOS+Mesa combo); set the decoder to `vaapi` to override"
+            );
+            "software".to_string()
+        } else {
+            choice
+        };
         if choice != "software" {
             match VaapiDecoder::new(codec_id) {
                 Ok(v) => {
@@ -456,6 +475,14 @@ impl VaapiDecoder {
             (*ctx).get_format = Some(pick_vaapi);
             (*ctx).flags |= ffi::AV_CODEC_FLAG_LOW_DELAY as i32;
             (*ctx).thread_count = 1; // hwaccel: threads only add latency
+
+            // The presenter holds mapped surfaces PAST receive_frame (the paintable's
+            // current texture + the newest frame in flight each pin one until GDK's
+            // release func) — surfaces libavcodec doesn't know are missing from its
+            // fixed-size VAAPI pool. Without headroom the decoder can recycle a surface
+            // the renderer is still sampling (intermittent block corruption) or fail
+            // allocation under scheduling jitter.
+            (*ctx).extra_hw_frames = 4;
             let r = ffi::avcodec_open2(ctx, codec, ptr::null_mut());
             if r < 0 {
                 let mut ctx = ctx;
diff --git a/crates/punktfunk-host/src/inject/linux/steam_controller.rs b/crates/punktfunk-host/src/inject/linux/steam_controller.rs
index 04cefbc..79373da 100644
--- a/crates/punktfunk-host/src/inject/linux/steam_controller.rs
+++ b/crates/punktfunk-host/src/inject/linux/steam_controller.rs
@@ -276,12 +276,43 @@ impl DeckTransport {
     }
 }
 
+/// One-shot diagnostic: InputPlumber (shipped and enabled by default on Bazzite) hidraw-grabs
+/// controllers it decides to manage and re-emits them under a different identity — historically
+/// the Deck config re-emitted an Xbox Elite pad with the trackpads routed to a mouse target. If
+/// it grabs our virtual Deck, everything downstream of hid-steam looks wrong (trackpads surface
+/// as a stick/mouse, gyro vanishes) while punktfunk's own logs stay clean — so name the suspect
+/// up front. Best-effort process-name scan; no dependency on its D-Bus API.
+fn warn_if_inputplumber() {
+    use std::sync::atomic::{AtomicBool, Ordering};
+    static ONCE: AtomicBool = AtomicBool::new(true);
+    if !ONCE.swap(false, Ordering::Relaxed) {
+        return;
+    }
+    let running = std::fs::read_dir("/proc")
+        .ok()
+        .into_iter()
+        .flatten()
+        .flatten()
+        .any(|e| {
+            std::fs::read_to_string(e.path().join("comm")).is_ok_and(|c| c.trim() == "inputplumber")
+        });
+    if running {
+        tracing::warn!(
+            "InputPlumber is running on this host — if it manages the virtual Steam Deck pad, \
+             games see InputPlumber's re-emitted device instead (trackpads may arrive as a \
+             stick/mouse, gyro may vanish). Check `inputplumber devices` and exclude the \
+             virtual pad from management if inputs look remapped."
+        );
+    }
+}
+
 /// Open the best Steam-Input-promotable Deck transport available, in preference order:
 /// **`raw_gadget` (SteamOS validated fast-path) → `usbip`/`vhci_hcd` (universal, Secure-Boot-clean)
 /// → UHID (universal, but `Interface: -1` so Steam Input won't promote it).** Each rung degrades to
 /// the next on failure, so a host lacking the gadget modules still gets a *promotable* Deck via
 /// usbip, and one lacking both still gets a working (if non-promoted) UHID pad.
 fn open_transport(idx: u8) -> Result<DeckTransport> {
+    warn_if_inputplumber();
     use crate::inject::{steam_gadget, steam_usbip};
     // 1. raw_gadget — the validated SteamOS fast-path (default on there).
     if steam_gadget::gadget_preferred() {