fix(bluetooth): wait for SCO link before Oboe restart + detect A2DP devices

Three fixes for Bluetooth audio not working:

1. is_bluetooth_available() now checks for TYPE_BLUETOOTH_A2DP (8) in
   addition to TYPE_BLUETOOTH_SCO (7) — many headsets only register as
   A2DP until SCO is explicitly started.

2. set_bluetooth_sco(on=true) polls isBluetoothScoOn() for up to 3s
   before restarting Oboe. startBluetoothSco() is async — the SCO link
   takes 500ms-2s to establish. Without waiting, Oboe opens against
   earpiece and audio goes nowhere.

3. Frontend skips redundant set_speakerphone(false) when transitioning
   to BT — start_bluetooth_sco() handles speaker-off internally,
   avoiding a double Oboe restart.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

desktop/src-tauri/src/android_audio.rs

@@ -185,10 +185,11 @@ pub fn is_bluetooth_sco_on() -> Result<bool, String> {
         .map_err(|e| format!("isBluetoothScoOn: {e}"))
 }
 
-/// Check whether a Bluetooth SCO-capable device is currently connected.
+/// Check whether a Bluetooth audio device is currently connected.
 ///
 /// Iterates `AudioManager.getDevices(GET_DEVICES_OUTPUTS)` and looks for
-/// `TYPE_BLUETOOTH_SCO` (7).
+/// any Bluetooth device type. Many headsets only register as A2DP until
+/// SCO is explicitly started, so we check for both SCO and A2DP types.
 pub fn is_bluetooth_available() -> Result<bool, String> {
     let (vm, activity) = jvm_and_activity()?;
     let mut env = vm
@@ -220,8 +221,9 @@ pub fn is_bluetooth_available() -> Result<bool, String> {
             .call_method(&device, "getType", "()I", &[])
             .and_then(|v| v.i())
             .unwrap_or(0);
-        // TYPE_BLUETOOTH_SCO = 7
-        if device_type == 7 {
+        // TYPE_BLUETOOTH_SCO = 7, TYPE_BLUETOOTH_A2DP = 8
+        if device_type == 7 || device_type == 8 {
+            tracing::info!(device_type, idx = i, "is_bluetooth_available: found BT device");
             return Ok(true);
         }
     }

desktop/src-tauri/src/lib.rs

@@ -779,6 +779,10 @@ async fn is_speakerphone_on() -> Result<bool, String> {
 
 /// Enable or disable Bluetooth SCO audio routing. Like speakerphone toggling,
 /// this requires an Oboe stream restart so AAudio picks up the new route.
+///
+/// `startBluetoothSco()` is asynchronous — the SCO link takes 500ms-2s to
+/// establish. We poll `isBluetoothScoOn()` up to 3 seconds before restarting
+/// Oboe, so the streams open against the BT device rather than earpiece.
 #[tauri::command]
 #[allow(unused_variables)]
 async fn set_bluetooth_sco(on: bool) -> Result<(), String> {
@@ -786,6 +790,21 @@ async fn set_bluetooth_sco(on: bool) -> Result<(), String> {
     {
         if on {
             android_audio::start_bluetooth_sco()?;
+            // Wait for SCO link to actually connect before restarting Oboe.
+            // startBluetoothSco() is async — jumping straight to Oboe restart
+            // would open streams against earpiece, not the BT device.
+            let mut connected = false;
+            for i in 0..30 {
+                tokio::time::sleep(std::time::Duration::from_millis(100)).await;
+                if android_audio::is_bluetooth_sco_on().unwrap_or(false) {
+                    tracing::info!(polls = i + 1, "set_bluetooth_sco: SCO connected");
+                    connected = true;
+                    break;
+                }
+            }
+            if !connected {
+                tracing::warn!("set_bluetooth_sco: SCO did not connect within 3s, proceeding anyway");
+            }
         } else {
             android_audio::stop_bluetooth_sco()?;
         }

desktop/src/main.ts

@@ -939,15 +939,17 @@ async function cycleAudioRoute() {
     const idx = routes.indexOf(currentAudioRoute);
     const next = routes[(idx + 1) % routes.length];
 
-    // Tear down current route
+    // Tear down current route, then activate next.
+    // start_bluetooth_sco() already calls setSpeakerphoneOn(false)
+    // internally, so we skip the separate speakerphone toggle when
+    // transitioning to BT to avoid a redundant Oboe restart.
     if (currentAudioRoute === "bluetooth") {
       await invoke("set_bluetooth_sco", { on: false });
     }
-    // Activate next route
     if (next === "speaker") {
       await invoke("set_speakerphone", { on: true });
     } else if (next === "bluetooth") {
-      await invoke("set_speakerphone", { on: false });
+      // BT start handles speaker-off internally + waits for SCO link
       await invoke("set_bluetooth_sco", { on: true });
     } else {
       // earpiece — turn everything off