Audio device: keep the new choice only once the devices reopen with it

ui.audio_device and Playback Engine › Apply wrote ui.audio before
apply_audio_config could refuse (while recording), so the saved choice no
longer matched the open device. apply_audio_config now takes the new
configuration and stores it only after the refusal check. Adds a test for
ui.audio_device: no-op query, a bad rate, refusal while recording, and an
applied change.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

crates/ui-egui/src/lib.rs

@@ -558,13 +558,15 @@ impl SoundApp {
             || (self.recorder.is_some() && self.engine.session().tracks.iter().any(|t| t.mixer.input_monitor || t.mixer.record_arm))
     }
 
-    /// Reopens the audio devices with `ui.audio` (Setup › Playback Engine › Apply), keeping the
-    /// transport position. Plugin instances and their editors are recreated with the new player.
-    /// Refused while recording, which would lose the take.
-    pub fn apply_audio_config(&mut self) -> Result<(), String> {
+    /// Reopens the audio devices with `cfg` (Setup › Playback Engine › Apply), keeping the
+    /// transport position, and keeps it as `ui.audio`. Plugin instances and their editors are
+    /// recreated with the new player. Refused while recording, which would lose the take; `ui.audio`
+    /// then stays the configuration of the open device.
+    pub fn apply_audio_config(&mut self, cfg: soundcraft_playback::AudioConfig) -> Result<(), String> {
         if self.engine.transport.recording {
             return Err("stop recording before changing the audio device".into());
         }
+        self.ui.audio = cfg;
         let at = self.position();
         if let Some(p) = &self.player {
             p.stop();

crates/ui-egui/src/windows.rs

@@ -547,11 +547,8 @@ pub fn playback_engine(app: &mut SoundApp, ctx: &egui::Context) {
     if refresh {
         audio_systems(ctx, true);
     }
-    if apply {
-        app.ui.audio = draft.clone();
-        if let Err(e) = app.apply_audio_config() {
-            app.ui.status = e;
-        }
+    if apply && let Err(e) = app.apply_audio_config(draft.clone()) {
+        app.ui.status = e;
     }
     if open {
         ctx.data_mut(|d| d.insert_temp(draft_id, draft));
@@ -588,8 +585,7 @@ pub fn audio_device_command(app: &mut SoundApp, p: &serde_json::Value) -> Result
         }
     }
     if changed {
-        app.ui.audio = cfg;
-        app.apply_audio_config()?;
+        app.apply_audio_config(cfg)?;
     }
     let device = app.player.as_ref().map(|pl| {
         json!({"name": pl.device_name, "sample_rate": pl.device_rate, "channels": pl.device_channels, "buffer_size": pl.device_buffer, "silent": pl.silent})

crates/ui-egui/tests/audio_device.rs

@@ -0,0 +1,27 @@
+//! `ui.audio_device`: the audio device choice is kept only once the devices reopen with it.
+use serde_json::json;
+use soundcraft_ui_egui::{Services, SoundApp};
+
+#[test]
+fn the_audio_device_choice_is_kept_only_when_it_is_applied() {
+    let mut app = SoundApp::new(soundcraft_engine::Engine::default(), None, Services::default());
+    let before = app.ui.audio.clone();
+
+    let r = app.run("ui.audio_device", json!({})).unwrap();
+    assert_eq!(r["config"], json!(before), "no change: just the choice and the device");
+
+    assert!(app.run("ui.audio_device", json!({"sample_rate": 12})).is_err());
+    assert_eq!(app.ui.audio, before, "an out-of-range rate changes nothing");
+
+    app.engine.transport.recording = true;
+    let err = app.run("ui.audio_device", json!({"buffer_size": 256, "output": "Elsewhere"})).unwrap_err();
+    assert!(err.contains("stop recording"), "{err}");
+    assert_eq!(app.ui.audio, before, "refused while recording: the saved choice stays the open device's");
+    app.engine.transport.recording = false;
+
+    // Opens the chosen device, or the default, or a silent clock without one.
+    let r = app.run("ui.audio_device", json!({"buffer_size": 256})).unwrap();
+    assert_eq!(app.ui.audio.buffer_size, Some(256));
+    assert_eq!(r["config"]["buffer_size"], 256);
+    assert!(r["device"].is_object(), "{r}");
+}