fix(shell): clip native_surface overlay to its panel's corner radius

The web canvas is a GPUI `native_surface` element, which on macOS
attaches an `NSView` (with a Metal-backed `CALayer`) as an AppKit
overlay on top of the GPUI render layer. GPUI's `overflow: hidden`
clips its own children but cannot reach into AppKit, so the canvas
painted square corners on top of the main panel's rounded edge —
the white surface visibly overshot the panel's rounded bottom.

Thread a per-corner radius through the GPUI patch:

- `Window::sync_native_surface` and the `PlatformWindow` trait carry
  a `Corners<Pixels>`.
- The macOS implementation sets `CALayer.cornerRadius` to the maximum
  requested radius and `maskedCorners` to the bitmask of corners that
  actually requested rounding (GPUI is Y-down while NSView is Y-up,
  so a GPUI "top" maps to a CALayer "MaxY" corner — comment locks
  the mapping). `setMasksToBounds: YES` lets Core Animation actually
  honor the corner radius for layered content.
- The `NativeSurface` element resolves all four corner radii from its
  own `StyleRefinement` (so callers attach `.rounded_bl(...)` /
  `.rounded_br(...)` exactly as on any other GPUI element).

Application side wires the right radius per context:

- The main canvas asks for `RADIUS_CARD` (18 px) on its bottom corners
  so it follows the surrounding panel's rounded bottom edge while
  the top stays flush against the toolbar.
- A split pane's canvas asks for the pane's own `SPLIT_PANE_RADIUS`
  (10 px) so the canvas hugs the rounded frame the pane already paints.

`render_failed_web_surface` doesn't need rounding wiring — the error
page is a GPUI div and is clipped normally by the surrounding
`overflow: hidden`.

crates/ely_app/src/shell/internal_pages.rs

@@ -40,7 +40,7 @@ use ely_browser_core::BrowserSnapshot;
 use ely_design_system::colors;
 use ely_domain::{ArchivedTab, BrowserTab, TabState};
 use gpui::{
-    AnyElement, Context, InteractiveElement, IntoElement, ParentElement, SharedString,
+    AnyElement, Context, InteractiveElement, IntoElement, ParentElement, Pixels, SharedString,
     StatefulInteractiveElement, Styled, div, px, rgb,
 };
 use gpui_component::{IconName, StyledExt, scroll::ScrollableElement};
@@ -54,6 +54,7 @@ impl ElyShell {
         &mut self,
         tab: &BrowserTab,
         snapshot: &BrowserSnapshot,
+        bottom_corner_radius: Pixels,
         cx: &mut Context<Self>,
     ) -> AnyElement {
         if tab.state() == &TabState::Crashed {
@@ -145,7 +146,7 @@ impl ElyShell {
                 render_settings_shell(snapshot, "ely://settings/sync", content, cx)
             }
             url if super::web_surface::is_external_web_url(url) => {
-                self.render_external_web_canvas(tab, snapshot, cx)
+                self.render_external_web_canvas(tab, snapshot, bottom_corner_radius, cx)
             }
             _ => render_default_page(tab),
         }

crates/ely_app/src/shell/splits.rs

@@ -16,6 +16,13 @@ use super::chrome::{
 use super::{ElyShell, ShellState};
 use crate::SplitRight;
 
+/// Bottom-corner radius applied to a split pane's canvas overlay so it
+/// follows the pane's rounded frame. Kept in lock-step with the
+/// `.rounded(px(10.0))` used in `render_pane`; bumping one without the
+/// other re-introduces the panel-bg sliver between the canvas and the
+/// pane's rounded edge.
+const SPLIT_PANE_RADIUS: f32 = 10.0;
+
 impl ElyShell {
     pub(super) fn render_content_area(
         &mut self,
@@ -24,11 +31,11 @@ impl ElyShell {
         cx: &mut Context<Self>,
     ) -> AnyElement {
         let Some(layout) = active_split_layout(snapshot, active_tab) else {
-            return self.render_web_canvas(active_tab, snapshot, cx);
+            return self.render_web_canvas(active_tab, snapshot, px(spacing::RADIUS_CARD), cx);
         };
 
         if layout.pane_count() < 2 {
-            return self.render_web_canvas(active_tab, snapshot, cx);
+            return self.render_web_canvas(active_tab, snapshot, px(spacing::RADIUS_CARD), cx);
         }
 
         self.render_split_canvas(snapshot, active_tab, layout, cx)
@@ -126,7 +133,7 @@ impl ElyShell {
             .collect::<Vec<_>>();
 
         if panes.len() < 2 {
-            return self.render_web_canvas(active_tab, snapshot, cx);
+            return self.render_web_canvas(active_tab, snapshot, px(spacing::RADIUS_CARD), cx);
         }
 
         let body = div()
@@ -217,7 +224,11 @@ impl ElyShell {
             .child(div().flex_1().min_h_0().overflow_hidden().child(if compact_canvas {
                 render_compact_split_canvas(tab)
             } else {
-                self.render_web_canvas(tab, snapshot, cx)
+                // Split pane wraps the canvas in a `rounded(SPLIT_PANE_RADIUS)`
+                // container with its own header — the canvas's bottom
+                // corners follow the pane's rounded edge, top stays
+                // flush against the pane header.
+                self.render_web_canvas(tab, snapshot, px(SPLIT_PANE_RADIUS), cx)
             }))
             .into_any_element()
     }

crates/ely_app/src/shell/web_surface_controller.rs

@@ -22,6 +22,7 @@ impl ElyShell {
         &mut self,
         tab: &BrowserTab,
         snapshot: &BrowserSnapshot,
+        bottom_corner_radius: Pixels,
         cx: &mut Context<Self>,
     ) -> AnyElement {
         let state_entity = cx.entity().clone();
@@ -31,16 +32,16 @@ impl ElyShell {
 
         match self.web_surfaces.state(tab.id()) {
             Some(WebSurfaceState::Ready(frame)) => {
-                render_ready_web_surface(frame, tab, state_entity)
+                render_ready_web_surface(frame, tab, state_entity, bottom_corner_radius)
             }
             Some(WebSurfaceState::Failed { message, .. }) => {
                 render_failed_web_surface(tab, message.as_str(), state_entity)
             }
             Some(WebSurfaceState::Loading { previous_frame: Some(frame), .. }) => {
-                render_ready_web_surface(frame, tab, state_entity)
+                render_ready_web_surface(frame, tab, state_entity, bottom_corner_radius)
             }
             Some(WebSurfaceState::Loading { previous_frame: None, .. }) | None => {
-                render_loading_web_surface(tab, state_entity)
+                render_loading_web_surface(tab, state_entity, bottom_corner_radius)
             }
         }
     }

crates/ely_app/src/shell/web_surface_view.rs

@@ -1,7 +1,7 @@
 use ely_domain::{BrowserTab, TabId};
 use gpui::{
     AnyElement, App, ElementId, Entity, InteractiveElement, IntoElement, MouseButton,
-    ParentElement, Styled, Window, canvas, div, native_surface, px, rgb,
+    ParentElement, Pixels, Styled, Window, canvas, div, native_surface, px, rgb,
 };
 
 use super::{
@@ -14,15 +14,25 @@ pub(super) fn render_ready_web_surface(
     _frame: &WebSurfaceFrame,
     tab: &BrowserTab,
     state_entity: Entity<ElyShell>,
+    bottom_corner_radius: Pixels,
 ) -> AnyElement {
-    render_web_surface(tab, state_entity.clone(), render_native_web_surface(tab, state_entity))
+    render_web_surface(
+        tab,
+        state_entity.clone(),
+        render_native_web_surface(tab, state_entity, bottom_corner_radius),
+    )
 }
 
 pub(super) fn render_loading_web_surface(
     tab: &BrowserTab,
     state_entity: Entity<ElyShell>,
+    bottom_corner_radius: Pixels,
 ) -> AnyElement {
-    render_web_surface(tab, state_entity.clone(), render_native_web_surface(tab, state_entity))
+    render_web_surface(
+        tab,
+        state_entity.clone(),
+        render_native_web_surface(tab, state_entity, bottom_corner_radius),
+    )
 }
 
 pub(super) fn render_failed_web_surface(
@@ -75,9 +85,18 @@ fn render_web_surface(
         .into_any_element()
 }
 
-fn render_native_web_surface(tab: &BrowserTab, state_entity: Entity<ElyShell>) -> impl IntoElement {
+fn render_native_web_surface(
+    tab: &BrowserTab,
+    state_entity: Entity<ElyShell>,
+    bottom_corner_radius: Pixels,
+) -> impl IntoElement {
     let tab_id = tab.id().clone();
     let element_id = ElementId::Name(format!("web-surface-{}", tab_id.as_str()).into());
+    // `bottom_corner_radius` is wired through the GPUI `native_surface`
+    // patch to the AppKit overlay's `CALayer.cornerRadius`, so the
+    // canvas follows the same rounded edge as its containing panel
+    // instead of painting past it. The top corners stay flat because
+    // the topbar / pane header sits flush above the canvas.
     native_surface(element_id, move |surface, bounds, window: &mut Window, cx: &mut App| {
         let scale_factor = window.scale_factor();
         state_entity.update(cx, |shell, cx| {
@@ -85,6 +104,8 @@ fn render_native_web_surface(tab: &BrowserTab, state_entity: Entity<ElyShell>) -
         });
     })
     .size_full()
+    .rounded_bl(bottom_corner_radius)
+    .rounded_br(bottom_corner_radius)
 }
 
 fn render_input_overlay(

third_party/gpui/src/elements/native_surface.rs

@@ -1,6 +1,6 @@
 use crate::{
-    App, Bounds, Element, ElementId, GlobalElementId, InspectorElementId, IntoElement, LayoutId,
-    NativeSurfaceHandle, Pixels, Style, StyleRefinement, Styled, Window,
+    App, Bounds, Corners, Element, ElementId, GlobalElementId, InspectorElementId, IntoElement,
+    LayoutId, NativeSurfaceHandle, Pixels, Style, StyleRefinement, Styled, Window,
 };
 use refineable::Refineable;
 
@@ -71,6 +71,20 @@ impl Element for NativeSurface {
         let Some(on_surface) = self.on_surface.as_mut() else {
             return;
         };
+        // The platform overlay sits on its own AppKit/Compositor layer
+        // and is not clipped by GPUI's rounded `overflow: hidden`.
+        // Resolve every corner radius from the element's style so a
+        // caller that attaches `.rounded_bl(...)` / `.rounded_br(...)`
+        // gets exactly those corners rounded on the platform surface.
+        let rem_size = window.rem_size();
+        let mut style = Style::default();
+        style.refine(&self.style);
+        let corner_radii = Corners {
+            top_left: style.corner_radii.top_left.to_pixels(rem_size),
+            top_right: style.corner_radii.top_right.to_pixels(rem_size),
+            bottom_left: style.corner_radii.bottom_left.to_pixels(rem_size),
+            bottom_right: style.corner_radii.bottom_right.to_pixels(rem_size),
+        };
         let Some(surface) = window.with_element_state::<NativeSurfaceState, _>(
             global_id,
             |state, window| {
@@ -78,7 +92,7 @@ impl Element for NativeSurface {
                     .and_then(|state| state.surface)
                     .or_else(|| window.create_native_surface());
                 if let Some(surface) = surface {
-                    window.sync_native_surface(&surface, bounds);
+                    window.sync_native_surface(&surface, bounds, corner_radii);
                     return (Some(surface.clone()), NativeSurfaceState { surface: Some(surface) });
                 }
                 (None, NativeSurfaceState { surface: None })

third_party/gpui/src/platform.rs

@@ -747,7 +747,13 @@ pub(crate) trait PlatformWindow: HasWindowHandle + HasDisplayHandle {
     fn create_native_surface(&self) -> Option<NativeSurfaceHandle> {
         None
     }
-    fn sync_native_surface(&self, _surface: &NativeSurfaceHandle, _bounds: Bounds<Pixels>) {}
+    fn sync_native_surface(
+        &self,
+        _surface: &NativeSurfaceHandle,
+        _bounds: Bounds<Pixels>,
+        _corner_radii: crate::Corners<Pixels>,
+    ) {
+    }
 
     // macOS specific methods
     fn get_title(&self) -> String {

third_party/gpui/src/platform/mac/window.rs

@@ -1539,7 +1539,12 @@ impl PlatformWindow for MacWindow {
         }
     }
 
-    fn sync_native_surface(&self, surface: &NativeSurfaceHandle, bounds: Bounds<Pixels>) {
+    fn sync_native_surface(
+        &self,
+        surface: &NativeSurfaceHandle,
+        bounds: Bounds<Pixels>,
+        corner_radii: crate::Corners<Pixels>,
+    ) {
         let this = self.0.lock();
         unsafe {
             let parent = this.native_view.as_ptr() as id;
@@ -1552,6 +1557,57 @@ impl PlatformWindow for MacWindow {
             let frame = NSRect::new(NSPoint::new(x, y), NSSize::new(width, height));
             let _: () = msg_send![view, setFrame: frame];
             let _: () = msg_send![view, setHidden: NO];
+
+            // Clip the AppKit overlay to the same shape the surrounding
+            // GPUI layout uses for its rounded panel. Without this the
+            // overlay's CALayer paints square corners on top of GPUI's
+            // rounded mask — the canvas visibly overshoots the panel's
+            // rounded bottom edge.
+            //
+            // Core Animation's `cornerRadius` is a single scalar applied
+            // to all four corners in `maskedCorners`; we therefore use
+            // the *maximum* requested radius across non-zero corners and
+            // intersect the corner mask to the corners that asked for
+            // any rounding. That covers the common cases:
+            //
+            // - Uniform `rounded_*`     : all four corners get the same radius.
+            // - Bottom-only `rounded_b_*`: top stays flush against a toolbar.
+            //
+            // GPUI is Y-down while NSView (with the default `isFlipped:
+            // NO`) is Y-up, so a GPUI *top* corner maps to a CALayer
+            // *MaxY* corner and a GPUI *bottom* corner maps to a CALayer
+            // *MinY* corner.
+            let layer: id = msg_send![view, layer];
+            if !layer.is_null() {
+                const LAYER_MIN_X_MIN_Y: NSUInteger = 1 << 0; // bottom-left in NSView
+                const LAYER_MAX_X_MIN_Y: NSUInteger = 1 << 1; // bottom-right
+                const LAYER_MIN_X_MAX_Y: NSUInteger = 1 << 2; // top-left
+                const LAYER_MAX_X_MAX_Y: NSUInteger = 1 << 3; // top-right
+
+                let tl = corner_radii.top_left.0.max(0.0);
+                let tr = corner_radii.top_right.0.max(0.0);
+                let bl = corner_radii.bottom_left.0.max(0.0);
+                let br = corner_radii.bottom_right.0.max(0.0);
+                let max_radius = tl.max(tr).max(bl).max(br) as f64;
+
+                let mut mask: NSUInteger = 0;
+                if tl > 0.0 {
+                    mask |= LAYER_MIN_X_MAX_Y;
+                }
+                if tr > 0.0 {
+                    mask |= LAYER_MAX_X_MAX_Y;
+                }
+                if bl > 0.0 {
+                    mask |= LAYER_MIN_X_MIN_Y;
+                }
+                if br > 0.0 {
+                    mask |= LAYER_MAX_X_MIN_Y;
+                }
+
+                let _: () = msg_send![layer, setCornerRadius: max_radius];
+                let _: () = msg_send![layer, setMaskedCorners: mask];
+                let _: () = msg_send![layer, setMasksToBounds: YES];
+            }
         }
     }
 

third_party/gpui/src/window.rs

@@ -3208,8 +3208,20 @@ impl Window {
     }
 
     /// Synchronizes a native child surface to a GPUI layout box.
-    pub fn sync_native_surface(&self, surface: &NativeSurfaceHandle, bounds: Bounds<Pixels>) {
-        self.platform_window.sync_native_surface(surface, bounds);
+    ///
+    /// `corner_radii` carries each rounded-corner radius (top-left,
+    /// top-right, bottom-left, bottom-right) so the platform surface
+    /// can match the surrounding GPUI layout's clipping shape — e.g.
+    /// a browser canvas whose top edge butts flat against a toolbar
+    /// while its bottom edge follows the panel's rounded corners.
+    /// Pass `Corners::default()` for a flat-edged surface.
+    pub fn sync_native_surface(
+        &self,
+        surface: &NativeSurfaceHandle,
+        bounds: Bounds<Pixels>,
+        corner_radii: crate::Corners<Pixels>,
+    ) {
+        self.platform_window.sync_native_surface(surface, bounds, corner_radii);
     }
 
     /// Removes an image from the sprite atlas.