sound: fix crash on guest connection by raising max queue size

The Linux virtio-sound driver requests a queue size of 256 by default.
The backend was capped at 64, causing set_vring_num to return InvalidParam
which propagated as an unhandled panic.

Also convert the terminal error panic to a logged error + exit(1) so
future unexpected daemon errors produce a meaningful log message.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

vhost-device-sound/src/device.rs

@@ -615,11 +615,7 @@ impl VhostUserBackend for VhostUserSoundBackend {
     }
 
     fn max_queue_size(&self) -> usize {
-        // The linux kernel driver does no checks for queue length and fails silently if
-        // a queue is filled up. In this case, adding an element to the queue
-        // returns ENOSPC and the element is not queued for a later attempt and
-        // is lost. `64` is a "good enough" value from our observations.
-        64
+        256
     }
 
     fn features(&self) -> u64 {

vhost-device-sound/src/lib.rs

@@ -328,13 +328,15 @@ pub fn start_backend_server(listener: &mut Listener, config: SoundConfig) {
 
     backend.send_exit_event();
 
-    if !matches!(
-        result,
+    match result {
+        Ok(()) => {}
         Err(vhost_user_backend::Error::HandleRequest(
-            vhost::vhost_user::Error::Disconnected | vhost::vhost_user::Error::PartialMessage
-        ))
-    ) {
-        result.unwrap();
+            vhost::vhost_user::Error::Disconnected | vhost::vhost_user::Error::PartialMessage,
+        )) => {}
+        Err(e) => {
+            log::error!("Daemon exited with error: {e}");
+            std::process::exit(1);
+        }
     }
 }