Test builds open no audio device (#2388)

Every headless test app built `GamePlugins`, whose `SoundPlugin` opened the default output device unless `$WOW_NOSOUND` or `$WOW_CAPTURE` was set, and no test run sets either. Under nextest that is one CoreAudio client and speaker stream per test process. With a few runs going at once, `coreaudiod` sat near 300% CPU, every sound on the machine crackled, and each test blocked on the audio server's connect.

A test build now takes the existing silent path, so its mixer is `None`, as with no device.

Test: `a_test_client_opens_no_audio_device`. With the change undone it fails on a machine with a speaker, taking 96 s; with it, the test passes in 0.06 s.

Fixes #2380

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
(cherry picked from commit fbc90b9bbf272a784f3703eb0c68ea466fe90951)

# Conflicts:
#	crates/benilla-app/src/game_plugins.rs
#	docs/DEVIATIONS.md

Absorbed into the octo fork. The sound/mod.rs fix applies unchanged. Of the tests the conflict hunk carried, only this commit's own a_test_client_opens_no_audio_device is kept, retargeted from upstream's headless_client_unrun to our headless_client (same contract: every plugin's build runs, no schedule does); resource_writers and the_glue_preview_has_one_feeder come from other upstream commits and need glue_scene and GluePreview, which this fork has not got.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SgstFWtn1RxEJ5kVrpgYwn

crates/benilla-app/src/game_plugins.rs

@@ -554,6 +554,15 @@ pub(crate) mod schedule_tests {
         c.systems.values().any(|s| s.name.contains("benilla_app::"))
     }
 
+    /// A test client opens no audio device: one stream per test process, one process per test,
+    /// floods the system audio server and crackles every sound on the machine.
+    #[test]
+    fn a_test_client_opens_no_audio_device() {
+        let app = headless_client();
+        let output = app.world().non_send_resource::<crate::sound::SoundOutput>();
+        assert!(output.mixer.is_none());
+    }
+
     /// One row of the class table: the type's name for the message, and its `TypeId`.
     type ClassRow = (&'static str, fn() -> TypeId);
 

crates/benilla-app/src/sound/mod.rs

@@ -224,8 +224,8 @@ fn feed_music_suppression(
     }
 }
 
-/// The backend output; `mixer` is `None` with no device or under `$WOW_NOSOUND`. Non-Send: the
-/// device stream is not `Send` on every platform, so audio systems run on the main thread.
+/// The backend output; `mixer` is `None` with no device, under `$WOW_NOSOUND` or in a test.
+/// Non-Send: the device stream is not `Send` on every platform, so audio systems run on the main thread.
 pub(crate) struct SoundOutput {
     pub(crate) mixer: Option<Mixer>,
     /// Live kit channels, pumped by [`kit::pump_channels`].
@@ -351,19 +351,21 @@ impl Plugin for SoundPlugin {
     fn build(&self, app: &mut App) {
         net::register(app);
         app.add_observer(on_cvar);
-        // `$WOW_NOSOUND` (a silent unattended run) and `$WOW_CAPTURE` open no device at all, so
-        // they never hold the audio hardware against a session someone is listening to.
+        // `$WOW_NOSOUND` (a silent unattended run), `$WOW_CAPTURE` and a test build open no device
+        // at all, so they never hold the audio hardware against a session someone is listening to.
         let silent = ["WOW_NOSOUND", "WOW_CAPTURE"]
             .into_iter()
-            .find(|v| std::env::var_os(v).is_some());
+            .find(|v| std::env::var_os(v).is_some())
+            .map(|v| format!("${v} set"))
+            .or_else(|| cfg!(test).then(|| "a test build".to_owned()));
         // Before the mixer: the probe's taps are main-track effects, fixed when kira builds it.
         let probe_dir = if silent.is_some() {
             None
         } else {
             probe::output_dir()
         };
-        let mixer = if let Some(var) = silent {
-            info!("${var} set — audio disabled");
+        let mixer = if let Some(why) = silent {
+            info!("{why} — audio disabled");
             None
         } else {
             match Mixer::new(probe_dir.as_deref()) {