fix(bluetooth): BT SCO mode skips 48kHz + VoiceCommunication on capture

Root cause: Oboe capture at 48kHz with InputPreset::VoiceCommunication
cannot open against a BT SCO device (only supports 8/16kHz). The stream
silently falls back to builtin mic, delivering zeros.

Fix: add bt_active flag to WzpOboeConfig. When set, capture skips
setSampleRate and setInputPreset, letting the system route to BT SCO
at its native rate. Oboe's SampleRateConversionQuality::Best resamples
to 48kHz for our ring buffers. Playout uses Usage::Media in BT mode.

New API: wzp_native_audio_start_bt() for BT mode, called from
set_bluetooth_sco(on=true). Normal audio_start() restores the
standard config when switching back to earpiece/speaker.

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

crates/wzp-native/cpp/oboe_bridge.cpp

@@ -254,18 +254,28 @@ int wzp_oboe_start(const WzpOboeConfig* config, const WzpOboeRings* rings) {
     oboe::AudioStreamBuilder captureBuilder;
     captureBuilder.setDirection(oboe::Direction::Input)
         ->setPerformanceMode(oboe::PerformanceMode::LowLatency)
-        // Shared mode allows Oboe's internal resampler to bridge 48kHz to
-        // the hardware rate (8/16kHz for BT SCO). Exclusive mode bypasses
-        // the resampler and fails with "getInputProfile could not find profile".
         ->setSharingMode(oboe::SharingMode::Shared)
         ->setFormat(oboe::AudioFormat::I16)
         ->setChannelCount(config->channel_count)
-        ->setSampleRate(config->sample_rate)
-        ->setFramesPerDataCallback(config->frames_per_burst)
-        ->setInputPreset(oboe::InputPreset::VoiceCommunication)
         ->setSampleRateConversionQuality(oboe::SampleRateConversionQuality::Best)
         ->setDataCallback(&g_capture_cb);
 
+    if (config->bt_active) {
+        // BT SCO mode: do NOT set sample rate or input preset.
+        // Requesting 48kHz against a BT SCO device fails with
+        // "getInputProfile could not find profile". Letting the system
+        // choose the native rate (8/16kHz) and relying on Oboe's
+        // resampler (SampleRateConversionQuality::Best) to bridge
+        // to our 48kHz ring buffer is the only path that works.
+        // InputPreset::VoiceCommunication can also prevent BT SCO
+        // routing on some devices — skip it for BT.
+        LOGI("capture: BT mode — no sample rate or input preset set");
+    } else {
+        captureBuilder.setSampleRate(config->sample_rate)
+            ->setFramesPerDataCallback(config->frames_per_burst)
+            ->setInputPreset(oboe::InputPreset::VoiceCommunication);
+    }
+
     oboe::Result result = captureBuilder.openStream(g_capture_stream);
     if (result != oboe::Result::OK) {
         LOGE("Failed to open capture stream: %s", oboe::convertToText(result));
@@ -321,12 +331,20 @@ int wzp_oboe_start(const WzpOboeConfig* config, const WzpOboeRings* rings) {
         ->setSharingMode(oboe::SharingMode::Shared)
         ->setFormat(oboe::AudioFormat::I16)
         ->setChannelCount(config->channel_count)
-        ->setSampleRate(config->sample_rate)
-        ->setFramesPerDataCallback(config->frames_per_burst)
-        ->setUsage(oboe::Usage::VoiceCommunication)
         ->setSampleRateConversionQuality(oboe::SampleRateConversionQuality::Best)
         ->setDataCallback(&g_playout_cb);
 
+    if (config->bt_active) {
+        LOGI("playout: BT mode — no sample rate set, using Usage::Media");
+        // Usage::Media instead of VoiceCommunication for BT output
+        // to avoid conflicts with the communication device routing.
+        playoutBuilder.setUsage(oboe::Usage::Media);
+    } else {
+        playoutBuilder.setSampleRate(config->sample_rate)
+            ->setFramesPerDataCallback(config->frames_per_burst)
+            ->setUsage(oboe::Usage::VoiceCommunication);
+    }
+
     result = playoutBuilder.openStream(g_playout_stream);
     if (result != oboe::Result::OK) {
         LOGE("Failed to open playout stream: %s", oboe::convertToText(result));

crates/wzp-native/cpp/oboe_bridge.h

@@ -16,6 +16,7 @@ typedef struct {
     int32_t sample_rate;
     int32_t frames_per_burst;
     int32_t channel_count;
+    int32_t bt_active;  /* nonzero = BT SCO mode: skip sample rate + input preset */
 } WzpOboeConfig;
 
 typedef struct {

crates/wzp-native/src/lib.rs

@@ -47,6 +47,10 @@ struct WzpOboeConfig {
     sample_rate: i32,
     frames_per_burst: i32,
     channel_count: i32,
+    /// When nonzero, capture stream skips setSampleRate and setInputPreset
+    /// so the system can route to BT SCO at its native rate (8/16kHz).
+    /// Oboe's SampleRateConversionQuality::Best resamples to 48kHz.
+    bt_active: i32,
 }
 
 #[repr(C)]
@@ -204,6 +208,17 @@ fn backend() -> &'static AudioBackend {
 /// Idempotent — calling while already running is a no-op that returns 0.
 #[unsafe(no_mangle)]
 pub extern "C" fn wzp_native_audio_start() -> i32 {
+    audio_start_inner(false)
+}
+
+/// Start Oboe in Bluetooth SCO mode — skips sample rate and input preset
+/// on capture so the system can route to the BT SCO device natively.
+#[unsafe(no_mangle)]
+pub extern "C" fn wzp_native_audio_start_bt() -> i32 {
+    audio_start_inner(true)
+}
+
+fn audio_start_inner(bt: bool) -> i32 {
     let b = backend();
     let mut started = match b.started.lock() {
         Ok(g) => g,
@@ -217,6 +232,7 @@ pub extern "C" fn wzp_native_audio_start() -> i32 {
         sample_rate: 48_000,
         frames_per_burst: FRAME_SAMPLES as i32,
         channel_count: 1,
+        bt_active: if bt { 1 } else { 0 },
     };
     let rings = WzpOboeRings {
         capture_buf: b.capture.buf_ptr(),