debug(touch): mirror PUNKTFUNK_TOUCH_DEBUG lines to a data-dir file

The presenter runs in the spawned punktfunk-session binary, whose stderr
Steam's game-mode reaper swallows on the Deck — so also append the finger/
mouse debug lines to $XDG_DATA_HOME/punktfunk-touch-debug.log (host-visible
under ~/.var/app/io.unom.Punktfunk), which survives regardless of how the
client is launched.

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

crates/pf-presenter/src/run.rs

@@ -427,6 +427,47 @@ fn run_inner(mut opts: SessionOpts, mut mode: ModeCtl) -> Result<Option<Outcome>
     // events on desktop, and the door Steam's on-screen keyboard types through under
     // gamescope). Toggled edge-wise — start/stop are not free on Wayland.
     let mut text_input_on = false;
+    // One-shot on-glass touch diagnostics. Under the Deck's game-mode gamescope, Steam Input
+    // owns the physical touchscreen and by default emulates it as a virtual trackpad/mouse —
+    // so the app may see MouseMotion/MouseButton instead of the Finger* events the touch-mode
+    // engine feeds on (which kills BOTH trackpad and passthrough at once). Set
+    // `PUNKTFUNK_TOUCH_DEBUG=1` to log every raw finger AND mouse event: one run tells us
+    // whether native wl_touch is being delivered (Finger* with direct=true) or intercepted.
+    let touch_debug = std::env::var_os("PUNKTFUNK_TOUCH_DEBUG").is_some();
+    // Under the Deck's game-mode gamescope the session binary's stderr is swallowed by Steam's
+    // reaper, so ALSO mirror the debug lines to a file in the app data dir (host-visible at
+    // ~/.var/app/io.unom.Punktfunk/…), pulled over SSH after a run.
+    let mut touch_log: Option<std::fs::File> = touch_debug
+        .then(|| {
+            let dir = std::env::var_os("XDG_DATA_HOME")
+                .map(std::path::PathBuf::from)
+                .or_else(|| {
+                    std::env::var_os("HOME").map(|h| std::path::PathBuf::from(h).join(".local/share"))
+                })
+                .unwrap_or_else(|| std::path::PathBuf::from("."));
+            let path = dir.join("punktfunk-touch-debug.log");
+            match std::fs::OpenOptions::new().create(true).append(true).open(&path) {
+                Ok(f) => {
+                    tracing::info!(path = %path.display(), "touch-debug: mirroring to file");
+                    Some(f)
+                }
+                Err(e) => {
+                    tracing::warn!(error = %e, "touch-debug: file sink open failed");
+                    None
+                }
+            }
+        })
+        .flatten();
+    // Defined after `touch_log` so the literal identifier resolves to that local; a no-op when
+    // the sink is absent (env unset or open failed).
+    macro_rules! touch_file_log {
+        ($($arg:tt)*) => {
+            if let Some(f) = touch_log.as_mut() {
+                use std::io::Write;
+                let _ = writeln!(f, $($arg)*);
+            }
+        };
+    }
 
     let outcome = 'main: loop {
         // --- SDL events (input, window, gamepads) ---------------------------------------
@@ -558,11 +599,19 @@ fn run_inner(mut opts: SessionOpts, mut mode: ModeCtl) -> Result<Option<Outcome>
                     }
                 }
                 Event::MouseMotion { xrel, yrel, .. } => {
+                    if touch_debug {
+                        tracing::info!(xrel, yrel, "touch-debug: MouseMotion");
+                        touch_file_log!("MouseMotion xrel={xrel} yrel={yrel}");
+                    }
                     if let Some(cap) = stream.as_mut().and_then(|s| s.capture.as_mut()) {
                         cap.on_motion(xrel, yrel);
                     }
                 }
                 Event::MouseButtonDown { mouse_btn, .. } => {
+                    if touch_debug {
+                        tracing::info!(?mouse_btn, "touch-debug: MouseButtonDown");
+                        touch_file_log!("MouseButtonDown mouse_btn={mouse_btn:?}");
+                    }
                     if let Some(cap) = stream.as_mut().and_then(|s| s.capture.as_mut()) {
                         if !cap.captured() {
                             // The engaging click is suppressed toward the host.
@@ -574,6 +623,10 @@ fn run_inner(mut opts: SessionOpts, mut mode: ModeCtl) -> Result<Option<Outcome>
                     }
                 }
                 Event::MouseButtonUp { mouse_btn, .. } => {
+                    if touch_debug {
+                        tracing::info!(?mouse_btn, "touch-debug: MouseButtonUp");
+                        touch_file_log!("MouseButtonUp mouse_btn={mouse_btn:?}");
+                    }
                     if let Some(cap) = stream.as_mut().and_then(|s| s.capture.as_mut()) {
                         cap.on_button_up(mouse_btn);
                     }
@@ -597,6 +650,20 @@ fn run_inner(mut opts: SessionOpts, mut mode: ModeCtl) -> Result<Option<Outcome>
                     timestamp,
                     ..
                 } => {
+                    if touch_debug {
+                        tracing::info!(
+                            touch_id,
+                            finger_id,
+                            x,
+                            y,
+                            direct = is_direct_touch(touch_id),
+                            "touch-debug: FingerDown"
+                        );
+                        touch_file_log!(
+                            "FingerDown touch_id={touch_id} finger_id={finger_id} x={x} y={y} direct={}",
+                            is_direct_touch(touch_id)
+                        );
+                    }
                     if is_direct_touch(touch_id)
                         && dispatch_finger(
                             FingerPhase::Down,
@@ -619,6 +686,20 @@ fn run_inner(mut opts: SessionOpts, mut mode: ModeCtl) -> Result<Option<Outcome>
                     timestamp,
                     ..
                 } => {
+                    if touch_debug {
+                        tracing::info!(
+                            touch_id,
+                            finger_id,
+                            x,
+                            y,
+                            direct = is_direct_touch(touch_id),
+                            "touch-debug: FingerMotion"
+                        );
+                        touch_file_log!(
+                            "FingerMotion touch_id={touch_id} finger_id={finger_id} x={x} y={y} direct={}",
+                            is_direct_touch(touch_id)
+                        );
+                    }
                     if is_direct_touch(touch_id)
                         && dispatch_finger(
                             FingerPhase::Move,
@@ -641,6 +722,20 @@ fn run_inner(mut opts: SessionOpts, mut mode: ModeCtl) -> Result<Option<Outcome>
                     timestamp,
                     ..
                 } => {
+                    if touch_debug {
+                        tracing::info!(
+                            touch_id,
+                            finger_id,
+                            x,
+                            y,
+                            direct = is_direct_touch(touch_id),
+                            "touch-debug: FingerUp"
+                        );
+                        touch_file_log!(
+                            "FingerUp touch_id={touch_id} finger_id={finger_id} x={x} y={y} direct={}",
+                            is_direct_touch(touch_id)
+                        );
+                    }
                     if is_direct_touch(touch_id)
                         && dispatch_finger(
                             FingerPhase::Up,