Support isolated live window ScreenCast streams

Render selected toplevels through a private portal-only capture protocol, preserve logical snapshot geometry, and renegotiate PipeWire video on window resizing. Bound outstanding snapshots and retry temporary contention; stop on source closure and session locking.

Validation: portal unit tests (31), capture budget unit, private-bus portal contracts, and real nested/PipeWire isolation, workspace, resize, close and paused-lock tests pass. Independent review cleared. Monitor restore integration timed out on both this build and the unchanged previous compositor under the current nested host.

crates/ferese-protocols/src/lib.rs

@@ -163,3 +163,69 @@ pub mod shell {
         }
     }
 }
+
+/// Private native portal window capture protocol.
+pub mod window_capture {
+    /// Version 1 of the native portal window capture protocol.
+    pub mod v1 {
+        #[cfg(feature = "client")]
+        pub use generated::client;
+        #[cfg(feature = "server")]
+        pub use generated::server;
+
+        mod generated {
+            #![allow(
+                dead_code,
+                non_camel_case_types,
+                non_upper_case_globals,
+                non_snake_case,
+                unused_imports,
+                unused_unsafe,
+                unused_variables,
+                clippy::all
+            )]
+
+            #[cfg(feature = "client")]
+            pub mod client {
+                use wayland_client;
+                use wayland_client::protocol::*;
+                use wayland_protocols_wlr::screencopy::v1::client::*;
+
+                pub mod __interfaces {
+                    use wayland_client::protocol::__interfaces::*;
+                    use wayland_protocols_wlr::screencopy::v1::client::__interfaces::*;
+
+                    wayland_scanner::generate_interfaces!(
+                        "../../protocols/ferese-window-capture-v1.xml"
+                    );
+                }
+                use self::__interfaces::*;
+
+                wayland_scanner::generate_client_code!(
+                    "../../protocols/ferese-window-capture-v1.xml"
+                );
+            }
+
+            #[cfg(feature = "server")]
+            pub mod server {
+                use wayland_protocols_wlr::screencopy::v1::server::*;
+                use wayland_server;
+                use wayland_server::protocol::*;
+
+                pub mod __interfaces {
+                    use wayland_protocols_wlr::screencopy::v1::server::__interfaces::*;
+                    use wayland_server::protocol::__interfaces::*;
+
+                    wayland_scanner::generate_interfaces!(
+                        "../../protocols/ferese-window-capture-v1.xml"
+                    );
+                }
+                use self::__interfaces::*;
+
+                wayland_scanner::generate_server_code!(
+                    "../../protocols/ferese-window-capture-v1.xml"
+                );
+            }
+        }
+    }
+}