feat(client/windows): invert scroll direction

The Apple client's toggle, wired through the shared session presenter:
Settings::invert_scroll -> SessionOpts -> Capture, applied at the single
seam where wheel deltas enter (before accumulation, so the fractional
remainders stay consistent with what was actually sent).

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

clients/session/src/console.rs

@@ -158,6 +158,7 @@ pub fn run(target: Option<&str>) -> u8 {
             v => v,
         },
         touch_mode: settings_at_start.touch_mode(),
+        invert_scroll: settings_at_start.invert_scroll,
         json_status,
         on_connected: Some(Box::new(move |fingerprint: [u8; 32]| {
             let fp_hex = trust::hex(&fingerprint);

clients/session/src/main.rs

@@ -373,6 +373,7 @@ mod session_main {
                 v => v,
             },
             touch_mode: settings.touch_mode(),
+            invert_scroll: settings.invert_scroll,
             json_status: true,
             on_connected: Some(Box::new(|fingerprint: [u8; 32]| {
                 // This host's card carries the accent bar in the desktop client now.

clients/windows/src/app/settings.rs

@@ -380,6 +380,10 @@ pub(crate) fn settings_page(
     let touch_combo = setting_combo(ctx, "Touch input", touch_names, touch_i, |s, i| {
         s.touch_mode = TOUCH_MODES[i].0.to_string();
     });
+    let invert_scroll_toggle =
+        setting_toggle(ctx, "Invert scroll direction", s.invert_scroll, |s, on| {
+            s.invert_scroll = on
+        });
     let shortcuts_toggle = setting_toggle(
         ctx,
         "Capture system shortcuts (Alt+Tab, Win, \u{2026})",
@@ -523,11 +527,17 @@ pub(crate) fn settings_page(
             );
             out.extend(group(
                 Some("Keyboard & mouse"),
-                vec![described(
-                    shortcuts_toggle,
-                    "Alt+Tab, the Windows key and friends reach the host while the stream has \
-                     input captured. Off, they act on this machine instead.",
-                )],
+                vec![
+                    described(
+                        shortcuts_toggle,
+                        "Alt+Tab, the Windows key and friends reach the host while the stream \
+                         has input captured. Off, they act on this machine instead.",
+                    ),
+                    described(
+                        invert_scroll_toggle,
+                        "Reverses the wheel and trackpad scroll direction sent to the host.",
+                    ),
+                ],
                 None,
             ));
             ("Input", out)

crates/pf-client-core/src/trust.rs

@@ -533,6 +533,10 @@ pub struct Settings {
     /// wait only adds a delay.
     #[serde(default = "default_true")]
     pub auto_wake: bool,
+    /// Reverse the wheel/trackpad scroll direction sent to the host (the Apple client's
+    /// "Invert scroll direction"). Default off = the host scrolls the way this machine does.
+    #[serde(default)]
+    pub invert_scroll: bool,
     /// Match-window resolution policy (design/midstream-resolution-resize.md D1): the
     /// stream mode follows the session window — the connect asks for the window's pixel
     /// size and a mid-session resize renegotiates the host's virtual display + encoder
@@ -622,6 +626,7 @@ impl Default for Settings {
             fullscreen_on_stream: true,
             library_enabled: false,
             auto_wake: true,
+            invert_scroll: false,
             match_window: false,
             last_window_w: 0,
             last_window_h: 0,

crates/pf-presenter/src/input.rs

@@ -53,6 +53,8 @@ pub struct Capture {
     /// The touchscreen input model for this session, and — for trackpad/pointer — the
     /// gesture state machine finger events feed.
     touch_mode: TouchMode,
+    /// Reverse the scroll direction sent to the host ([`Settings::invert_scroll`]).
+    invert_scroll: bool,
     gestures: Gestures,
 }
 
@@ -68,7 +70,11 @@ fn send(connector: &NativeClient, kind: InputKind, code: u32, x: i32, y: i32, fl
 }
 
 impl Capture {
-    pub fn new(connector: Arc<NativeClient>, touch_mode: TouchMode) -> Capture {
+    pub fn new(
+        connector: Arc<NativeClient>,
+        touch_mode: TouchMode,
+        invert_scroll: bool,
+    ) -> Capture {
         Capture {
             connector,
             captured: false,
@@ -79,6 +85,7 @@ impl Capture {
             scroll_acc: (0.0, 0.0),
             touch_slots: HashMap::new(),
             touch_mode,
+            invert_scroll,
             gestures: Gestures::new(touch_mode == TouchMode::Trackpad),
         }
     }
@@ -194,9 +201,10 @@ impl Capture {
             return;
         }
         self.flush_motion(); // scroll happens at the latest cursor position
+        let sign = if self.invert_scroll { -1.0 } else { 1.0 };
         let (mut ax, mut ay) = self.scroll_acc;
-        ay += f64::from(dy) * 120.0;
-        ax += f64::from(dx) * 120.0;
+        ay += f64::from(dy) * 120.0 * sign;
+        ax += f64::from(dx) * 120.0 * sign;
         let vy = ay.trunc() as i32;
         if vy != 0 {
             ay -= f64::from(vy);

crates/pf-presenter/src/run.rs

@@ -48,6 +48,8 @@ pub struct SessionOpts {
     /// `Pointer` (absolute cursor), or `Touch` (real multi-touch passthrough). Latched per
     /// session — a mouse-only client leaves this at the default and never sees a finger.
     pub touch_mode: TouchMode,
+    /// Reverse the scroll direction sent to the host ([`Settings::invert_scroll`]).
+    pub invert_scroll: bool,
     /// Emit the `{"ready":true}` stdout line after the first presented frame.
     pub json_status: bool,
     /// Called once on `Connected` with the host's fingerprint (trust persistence is the
@@ -811,7 +813,7 @@ fn run_inner(mut opts: SessionOpts, mut mode: ModeCtl) -> Result<Option<Outcome>
                         .ok();
                     gamepad.attach(c.clone());
                     st.clock_offset = Some(c.clock_offset_shared());
-                    let mut cap = Capture::new(c.clone(), opts.touch_mode);
+                    let mut cap = Capture::new(c.clone(), opts.touch_mode, opts.invert_scroll);
                     cap.engage(); // capture engages when the stream starts (ui_stream parity)
                     apply_capture(&mut window, &mouse, true);
                     st.capture = Some(cap);