fix(apple): resolve QoS priority inversions + two Swift concurrency warnings

Priority inversions (Thread Performance Checker): the Apple client drains every
plane on .userInteractive threads (video pump, audio, gamepad feedback) and
connects on a .userInitiated Task, but the connector's producer threads ran at
the default QoS — so a high-QoS consumer parked waiting on a lower-QoS producer.
Pin the connector's producers (outer worker thread, all tokio runtime threads via
on_thread_start, and the data-plane spawn_blocking pump) to .userInteractive on
Apple so they match the consumers. #[cfg(target_vendor = "apple")] helper using
the existing libc dep; no-op off Apple, no Swift-side change (no latency
regression).

GamepadFeedback.swift: the init's MainActor hop captured self implicitly-strong
while the inner $active sink captured it weakly — capture [weak self] in the hop
too (the sink stays weak to avoid the retain cycle).

StreamPump.swift: the @Sendable pump-thread closure captured the non-Sendable
AVSampleBufferDisplayLayer. enqueue/flush are documented thread-safe and only the
pump thread drives it after start(), so assert that with nonisolated(unsafe).

cargo build/test/clippy/fmt green (core + host); xcframework rebuilt; swift build
+ iOS/tvOS targets clean with both warnings gone. Runtime confirmation of the
inversion warnings needs a GUI run under Xcode's Thread Performance Checker.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/punktfunk-core/src/client.rs

@@ -153,6 +153,25 @@ pub struct NativeClient {
     pub clock_offset_ns: i64,
 }
 
+/// Pin the calling thread to the user-interactive QoS class on Apple targets.
+///
+/// The Apple client drains every plane on `.userInteractive` Thread s (video pump, audio,
+/// gamepad feedback) and connects on a `.userInitiated` Task. Those consumers block on the
+/// std channels these worker threads feed; if the producers run at the default QoS, the
+/// kernel sees a high-QoS thread parked waiting on a lower-QoS one and the Thread Performance
+/// Checker flags a priority inversion. Matching the producers to the consumers' QoS removes
+/// the inversion without slowing the Swift side. No-op off Apple (the Linux client/host don't
+/// run a QoS scheduler, and `punktfunk-client-rs` doesn't care).
+#[cfg(target_vendor = "apple")]
+fn pin_thread_user_interactive() {
+    // SAFETY: sets only the current thread's QoS class — always valid to call.
+    unsafe {
+        libc::pthread_set_qos_class_self_np(libc::qos_class_t::QOS_CLASS_USER_INTERACTIVE, 0);
+    }
+}
+#[cfg(not(target_vendor = "apple"))]
+fn pin_thread_user_interactive() {}
+
 impl NativeClient {
     /// Connect to a `punktfunk/1` host and start the session at (up to) `mode`. Blocks until the
     /// handshake completes or `timeout` elapses.
@@ -197,8 +216,12 @@ impl NativeClient {
         let worker = std::thread::Builder::new()
             .name("punktfunk-client".into())
             .spawn(move || {
+                pin_thread_user_interactive(); // this thread drives the runtime + handshake
                 let rt = match tokio::runtime::Builder::new_multi_thread()
                     .worker_threads(2)
+                    // Every runtime thread (async workers + the spawn_blocking pool that runs
+                    // the data-plane pump) matches the Apple client's QoS — no priority inversion.
+                    .on_thread_start(pin_thread_user_interactive)
                     .enable_all()
                     .build()
                 {
@@ -839,6 +862,7 @@ async fn worker_main(args: WorkerArgs) {
     let pump_shutdown = shutdown.clone();
     let pump_probe = probe.clone();
     let _ = tokio::task::spawn_blocking(move || {
+        pin_thread_user_interactive(); // feeds frame_tx → the client's user-interactive video pump
         while !pump_shutdown.load(Ordering::SeqCst) {
             match session.poll_frame() {
                 Ok(frame) => {