feat: add WindowIdExt::with_window_handle for native window handle access

src/window/id.rs

@@ -216,6 +216,18 @@ pub trait WindowIdExt: WindowIdExtSealed {
     /// Get the dots-per-inch scaling of this window or 1.0 if the platform does not
     /// support it (Android).
     fn scale(&self) -> f64;
+
+    /// Run a closure with this window's native [`raw_window_handle::WindowHandle`], returning the
+    /// closure's result, or `None` if there is no live OS window for this id (or the platform could
+    /// not produce a handle).
+    ///
+    /// This is a backend-neutral handle (`raw-window-handle` is a crate Floem already depends on),
+    /// so embedders can integrate native children — e.g. attaching a child webview via `wry`'s
+    /// `build_as_child` — against the parent window without Floem exposing its windowing-backend
+    /// types. The handle is only valid for the duration of `f`.
+    fn with_window_handle<F, T>(&self, f: F) -> Option<T>
+    where
+        F: FnOnce(raw_window_handle::WindowHandle<'_>) -> T;
 }
 
 impl WindowIdExt for WindowId {
@@ -279,6 +291,17 @@ impl WindowIdExt for WindowId {
     fn scale(&self) -> f64 {
         with_window(self, |window| window.scale_factor()).unwrap_or(1.0)
     }
+
+    fn with_window_handle<F, T>(&self, f: F) -> Option<T>
+    where
+        F: FnOnce(raw_window_handle::WindowHandle<'_>) -> T,
+    {
+        use raw_window_handle::HasWindowHandle;
+        // `Window: HasWindowHandle` (Floem already relies on this internally to build its render
+        // surface); hand the closure the resulting `WindowHandle`, which itself impls
+        // `HasWindowHandle` for use with e.g. `wry`'s `build_as_child`.
+        with_window(self, move |window| window.window_handle().ok().map(f)).flatten()
+    }
 }
 
 /// Called by `ApplicationHandle` at the end of the event loop callback.