SFU M1: libwebrtc Janus publish/subscribe behind dev gate.

Add stream-webrtc lab activity with REST join + Janus WS trickle,
WebView issues login for session cookies, and developer settings toggle
without lifting ALPHA_FEATURE_FREEZE.

Co-authored-by: Cursor <cursoragent@cursor.com>

app/build.gradle

@@ -151,6 +151,7 @@ dependencies {
 
     testImplementation 'junit:junit:4.13.2'
     testImplementation 'org.json:json:20240303'
+    testImplementation 'org.robolectric:robolectric:4.11.1'
 
     implementation 'com.github.mwiede:jsch:0.2.21'
 
@@ -159,5 +160,9 @@ dependencies {
     implementation 'org.bouncycastle:bcprov-jdk18on:1.78.1'
     implementation 'org.slf4j:slf4j-android:1.7.36'
 
+    // SFU lab (M1): libwebrtc publish/subscribe to Janus VideoRoom (dev-gated).
+    implementation 'io.getstream:stream-webrtc-android:1.1.3'
+    implementation 'com.squareup.okhttp3:okhttp:4.12.0'
+
     implementation project(':tunnel')
 }

app/src/main/AndroidManifest.xml

@@ -67,6 +67,18 @@
             android:label="@string/developer_settings_title"
             android:parentActivityName=".MainActivity" />
 
+        <activity
+            android:name=".sfu.SfuLabActivity"
+            android:exported="false"
+            android:label="@string/sfu_lab_title"
+            android:parentActivityName=".DeveloperSettingsActivity" />
+
+        <activity
+            android:name=".sfu.SfuLoginActivity"
+            android:exported="false"
+            android:label="@string/sfu_lab_login"
+            android:parentActivityName=".sfu.SfuLabActivity" />
+
         <activity
             android:name=".qr.QrScanActivity"
             android:exported="false"

app/src/main/java/com/foxx/androidcast/AppPreferences.java

@@ -63,6 +63,8 @@ public final class AppPreferences {
 
     private static final String KEY_DEV_WIRED_DISPLAY_HINTS = "dev_wired_display_hints";
     private static final String KEY_DEV_USB_TETHER_TRANSPORT = "dev_usb_tether_transport";
+    private static final String KEY_DEV_SFU_RELAY = "dev_sfu_relay";
+    private static final String KEY_DEV_SFU_SESSION_COOKIE = "dev_sfu_session_cookie";
     private static final String KEY_DEV_SENDER_RESOLUTION_UI_MODE = "dev_sender_resolution_ui_mode";
     private static final String KEY_DEV_EXTERNAL_CAPTURE_POLICY = "dev_external_capture_policy";
     private static final String KEY_DEV_COMMERCIAL_ADS = "dev_commercial_ads";
@@ -386,7 +388,7 @@ public final class AppPreferences {
             s.setNetworkAdoption(CastSettings.NetworkAdoption.ESTIMATED);
         }
         s.setCodecHardening(getSenderCodecHardening(context));
-        clampAlphaTransport(s);
+        clampAlphaTransport(context, s);
         return s;
     }
 
@@ -455,6 +457,24 @@ public final class AppPreferences {
         prefs(context).edit().putBoolean(KEY_DEV_USB_TETHER_TRANSPORT, enabled).apply();
     }
 
+    /** Developer: Janus SFU relay lab (libwebrtc publish/subscribe). */
+    public static boolean isDevSfuRelayEnabled(Context context) {
+        return prefs(context).getBoolean(KEY_DEV_SFU_RELAY, false);
+    }
+
+    public static void setDevSfuRelayEnabled(Context context, boolean enabled) {
+        prefs(context).edit().putBoolean(KEY_DEV_SFU_RELAY, enabled).apply();
+    }
+
+    /** Optional fallback session cookie if WebView jar is empty. */
+    public static String getDevSfuSessionCookie(Context context) {
+        return prefs(context).getString(KEY_DEV_SFU_SESSION_COOKIE, "");
+    }
+
+    public static void setDevSfuSessionCookie(Context context, String cookie) {
+        prefs(context).edit().putString(KEY_DEV_SFU_SESSION_COOKIE, cookie != null ? cookie : "").apply();
+    }
+
     /** Default: {@link SenderResolutionUiMode#SEPARATED}. */
     public static SenderResolutionUiMode getDevSenderResolutionUiMode(Context context) {
         String name = prefs(context).getString(
@@ -759,7 +779,7 @@ public final class AppPreferences {
             s.setNetworkAdoption(CastSettings.NetworkAdoption.ESTIMATED);
         }
         s.setCodecHardening(getReceiverCodecHardening(context));
-        clampAlphaTransport(s);
+        clampAlphaTransport(context, s);
         return s;
     }
 
@@ -835,13 +855,18 @@ public final class AppPreferences {
         return fallback;
     }
 
-    private static void clampAlphaTransport(CastSettings settings) {
+    private static void clampAlphaTransport(Context context, CastSettings settings) {
         if (settings == null || !CastConfig.ALPHA_FEATURE_FREEZE) {
             return;
         }
-        if (!CastConfig.isReleaseTransport(settings.getTransport())) {
+        if (CastConfig.isReleaseTransport(settings.getTransport())) {
-            settings.setTransport(CastConfig.DEFAULT_TRANSPORT);
+            return;
         }
+        if (CastConfig.TRANSPORT_WEBRTC.equals(settings.getTransport())
+                && isDevSfuRelayEnabled(context)) {
+            return;
+        }
+        settings.setTransport(CastConfig.DEFAULT_TRANSPORT);
     }
 
     public static String getEntitlementAccountKey(Context context) {

app/src/main/java/com/foxx/androidcast/CastSettingsBinder.java

@@ -245,6 +245,10 @@ public final class CastSettingsBinder {
             labelList.add(activity.getString(R.string.transport_usb_tether));
             valueList.add(CastConfig.TRANSPORT_USB_TETHER);
         }
+        if (com.foxx.androidcast.sfu.SfuRelayGate.isAvailable(activity)) {
+            labelList.add(activity.getString(R.string.transport_webrtc));
+            valueList.add(CastConfig.TRANSPORT_WEBRTC);
+        }
         String[] labels = labelList.toArray(new String[0]);
         String[] values = valueList.toArray(new String[0]);
         bindStringSpinner(spinner, labels, values, settings.getTransport(), v -> {

app/src/main/java/com/foxx/androidcast/DeveloperSettingsActivity.java

@@ -130,6 +130,7 @@ public class DeveloperSettingsActivity extends AppCompatActivity {
         bindDiagPingSection();
         bindSenderResolutionUiModeSection();
         bindWiredDisplaySection();
+        bindSfuLabSection();
         bindAdbWifiSection();
         bindCommercialSection();
     }
@@ -170,10 +171,24 @@ public class DeveloperSettingsActivity extends AppCompatActivity {
         bindRemoteAccessSection();
         bindSenderResolutionUiModeSection();
         bindWiredDisplaySection();
+        bindSfuLabSection();
         bindAdbWifiSection();
         bindCommercialSection();
     }
 
+    private void bindSfuLabSection() {
+        CheckBox sfu = findViewById(R.id.check_dev_sfu_relay);
+        Button openLab = findViewById(R.id.btn_open_sfu_lab);
+        if (sfu == null) {
+            return;
+        }
+        bindDeveloperCheckbox(sfu, AppPreferences.isDevSfuRelayEnabled(this),
+                AppPreferences::setDevSfuRelayEnabled);
+        if (openLab != null) {
+            openLab.setOnClickListener(v -> com.foxx.androidcast.sfu.SfuLabActivity.openIfAvailable(this));
+        }
+    }
+
     private void bindAdbWifiSection() {
         if (!BuildConfig.DEBUG) {
             android.view.View section = findViewById(R.id.check_dev_adb_wifi_keeper);

app/src/main/java/com/foxx/androidcast/sfu/JanusWebSocketClient.java

@@ -0,0 +1,109 @@
+package com.foxx.androidcast.sfu;
+
+import android.util.Log;
+
+import org.json.JSONObject;
+
+import java.util.concurrent.atomic.AtomicInteger;
+
+import okhttp3.OkHttpClient;
+import okhttp3.Request;
+import okhttp3.Response;
+import okhttp3.WebSocket;
+import okhttp3.WebSocketListener;
+
+/** Janus Gateway WebSocket for trickle ICE + keepalive on an existing REST session. */
+public final class JanusWebSocketClient {
+    private static final String TAG = "JanusWS";
+
+    public interface Listener {
+        void onTrickle(JSONObject candidate);
+
+        void onFailure(String message);
+    }
+
+    private final OkHttpClient http = new OkHttpClient();
+    private final AtomicInteger tx = new AtomicInteger();
+    private WebSocket webSocket;
+    private Listener listener;
+    private long sessionId;
+    private long handleId;
+
+    public void connect(long sessionId, long handleId, Listener listener) {
+        this.sessionId = sessionId;
+        this.handleId = handleId;
+        this.listener = listener;
+        Request req = new Request.Builder().url(SfuEndpoints.webSocketUrl()).build();
+        webSocket = http.newWebSocket(req, new WebSocketListener() {
+            @Override
+            public void onOpen(WebSocket webSocket, Response response) {
+                Log.d(TAG, "open");
+            }
+
+            @Override
+            public void onMessage(WebSocket webSocket, String text) {
+                handleMessage(text);
+            }
+
+            @Override
+            public void onFailure(WebSocket webSocket, Throwable t, Response response) {
+                if (listener != null) {
+                    listener.onFailure(t.getMessage() != null ? t.getMessage() : "websocket failed");
+                }
+            }
+        });
+    }
+
+    public void sendTrickle(JSONObject candidate) {
+        if (webSocket == null) {
+            return;
+        }
+        try {
+            JSONObject msg = new JSONObject();
+            msg.put("janus", "trickle");
+            msg.put("transaction", "tx-" + tx.incrementAndGet());
+            msg.put("session_id", sessionId);
+            msg.put("handle_id", handleId);
+            msg.put("candidate", candidate);
+            webSocket.send(msg.toString());
+        } catch (org.json.JSONException e) {
+            Log.w(TAG, "trickle encode", e);
+        }
+    }
+
+    public void sendKeepalive() {
+        if (webSocket == null) {
+            return;
+        }
+        try {
+            JSONObject msg = new JSONObject();
+            msg.put("janus", "keepalive");
+            msg.put("transaction", "tx-" + tx.incrementAndGet());
+            msg.put("session_id", sessionId);
+            webSocket.send(msg.toString());
+        } catch (org.json.JSONException e) {
+            Log.w(TAG, "keepalive encode", e);
+        }
+    }
+
+    public void close() {
+        if (webSocket != null) {
+            webSocket.close(1000, "done");
+            webSocket = null;
+        }
+    }
+
+    private void handleMessage(String text) {
+        try {
+            JSONObject msg = new JSONObject(text);
+            if ("trickle".equals(msg.optString("janus")) && listener != null) {
+                JSONObject candidate = msg.optJSONObject("candidate");
+                if (candidate != null) {
+                    listener.onTrickle(candidate);
+                }
+            }
+        } catch (org.json.JSONException e) {
+            Log.w(TAG, "parse", e);
+        }
+    }
+}

app/src/main/java/com/foxx/androidcast/sfu/SfuAuthStore.java

@@ -0,0 +1,31 @@
+package com.foxx.androidcast.sfu;
+
+import android.content.Context;
+import android.webkit.CookieManager;
+
+import com.foxx.androidcast.AppPreferences;
+
+/** Session cookies for SFU REST API (shared {@code ac_crash_sess} with issues console). */
+public final class SfuAuthStore {
+    private SfuAuthStore() {}
+
+    public static boolean hasSession(Context context) {
+        String cookie = cookieHeader(context);
+        return cookie != null && !cookie.isEmpty();
+    }
+
+    public static String cookieHeader(Context context) {
+        CookieManager cm = CookieManager.getInstance();
+        String fromWebView = cm.getCookie(SfuEndpoints.origin());
+        if (fromWebView != null && !fromWebView.trim().isEmpty()) {
+            return fromWebView.trim();
+        }
+        return AppPreferences.getDevSfuSessionCookie(context);
+    }
+
+    public static void clear(Context context) {
+        CookieManager cm = CookieManager.getInstance();
+        cm.setCookie(SfuEndpoints.origin(), "");
+        AppPreferences.setDevSfuSessionCookie(context, "");
+    }
+}

app/src/main/java/com/foxx/androidcast/sfu/SfuEndpoints.java

@@ -0,0 +1,34 @@
+package com.foxx.androidcast.sfu;
+
+import com.foxx.androidcast.network.BackendEndpoints;
+
+/** Resolved SFU URLs on the production apps host. */
+public final class SfuEndpoints {
+    private static final String ORIGIN = "https://" + BackendEndpoints.APPS_HOST;
+
+    private SfuEndpoints() {}
+
+    public static String origin() {
+        return ORIGIN;
+    }
+
+    public static String apiBase() {
+        return ORIGIN + SfuRelayGate.API_BASE;
+    }
+
+    public static String joinUrl() {
+        return apiBase() + "/join";
+    }
+
+    public static String roomsUrl() {
+        return apiBase() + "/rooms";
+    }
+
+    public static String healthUrl() {
+        return SfuRelayGate.healthUrl(ORIGIN);
+    }
+
+    public static String webSocketUrl() {
+        return "wss://" + BackendEndpoints.APPS_HOST + SfuRelayGate.WS_PATH;
+    }
+}

app/src/main/java/com/foxx/androidcast/sfu/SfuLabActivity.java

@@ -0,0 +1,204 @@
+package com.foxx.androidcast.sfu;
+
+import android.content.Context;
+import android.content.Intent;
+import android.os.Bundle;
+import android.os.Handler;
+import android.os.Looper;
+import android.text.method.ScrollingMovementMethod;
+import android.widget.Button;
+import android.widget.EditText;
+import android.widget.TextView;
+import android.widget.Toast;
+
+import androidx.activity.result.ActivityResultLauncher;
+import androidx.activity.result.contract.ActivityResultContracts;
+import androidx.appcompat.app.AppCompatActivity;
+
+import com.foxx.androidcast.CastThemeHelper;
+import com.foxx.androidcast.R;
+
+import org.webrtc.SurfaceViewRenderer;
+
+/** Dev-only SFU lab: libwebrtc publish/subscribe to Janus VideoRoom (M1). */
+public class SfuLabActivity extends AppCompatActivity implements SfuRtcSession.Callback {
+    private static final int REQ_LOGIN = 9108;
+
+    private SurfaceViewRenderer localVideo;
+    private SurfaceViewRenderer remoteVideo;
+    private TextView logView;
+    private TextView statusView;
+    private SfuRtcSession session;
+    private final Handler main = new Handler(Looper.getMainLooper());
+    private final StringBuilder logBuf = new StringBuilder();
+
+    private final ActivityResultLauncher<Intent> loginLauncher =
+            registerForActivityResult(new ActivityResultContracts.StartActivityForResult(), result -> {
+                refreshAuthStatus();
+            });
+
+    public static void openIfAvailable(Context context) {
+        if (!SfuRelayGate.isAvailable(context)) {
+            Toast.makeText(context, R.string.sfu_lab_unavailable, Toast.LENGTH_LONG).show();
+            return;
+        }
+        context.startActivity(new Intent(context, SfuLabActivity.class));
+    }
+
+    @Override
+    protected void attachBaseContext(Context newBase) {
+        super.attachBaseContext(com.foxx.androidcast.CastLocaleHelper.attach(newBase));
+    }
+
+    @Override
+    protected void onCreate(Bundle savedInstanceState) {
+        CastThemeHelper.applyTheme(this);
+        super.onCreate(savedInstanceState);
+        if (!SfuRelayGate.isAvailable(this)) {
+            Toast.makeText(this, R.string.sfu_lab_unavailable, Toast.LENGTH_LONG).show();
+            finish();
+            return;
+        }
+        setContentView(R.layout.activity_sfu_lab);
+        setTitle(R.string.sfu_lab_title);
+
+        localVideo = findViewById(R.id.sfu_local_video);
+        remoteVideo = findViewById(R.id.sfu_remote_video);
+        logView = findViewById(R.id.text_sfu_log);
+        statusView = findViewById(R.id.text_sfu_lab_status);
+        logView.setMovementMethod(new ScrollingMovementMethod());
+
+        SfuRtcSession.ensureFactory(this);
+        org.webrtc.EglBase.Context egl = SfuRtcSession.eglContext();
+        localVideo.init(egl, null);
+        remoteVideo.init(egl, null);
+        localVideo.setMirror(true);
+
+        session = new SfuRtcSession(this, this);
+        session.attachLocalRenderer(localVideo);
+        session.attachRemoteRenderer(remoteVideo);
+
+        Button login = findViewById(R.id.btn_sfu_login);
+        login.setOnClickListener(v -> loginLauncher.launch(new Intent(this, SfuLoginActivity.class)));
+
+        findViewById(R.id.btn_sfu_create_room).setOnClickListener(v -> createRoom());
+        findViewById(R.id.btn_sfu_publish).setOnClickListener(v -> publish());
+        findViewById(R.id.btn_sfu_subscribe).setOnClickListener(v -> subscribe());
+        findViewById(R.id.btn_sfu_stop).setOnClickListener(v -> stopSession());
+
+        refreshAuthStatus();
+        probeHealth();
+    }
+
+    @Override
+    protected void onDestroy() {
+        stopSession();
+        localVideo.release();
+        remoteVideo.release();
+        super.onDestroy();
+    }
+
+    private void refreshAuthStatus() {
+        boolean authed = SfuAuthStore.hasSession(this);
+        statusView.setText(getString(authed ? R.string.sfu_lab_authed : R.string.sfu_lab_need_login));
+    }
+
+    private void probeHealth() {
+        new Thread(() -> {
+            try {
+                SfuSignalingClient client = new SfuSignalingClient(this);
+                org.json.JSONObject health = client.health();
+                String status = health.optJSONObject("sfu").optString("status", "?");
+                runOnUiThread(() -> onLog("SFU health: " + status));
+            } catch (Exception e) {
+                runOnUiThread(() -> onLog("Health check failed: " + e.getMessage()));
+            }
+        }).start();
+    }
+
+    private void createRoom() {
+        new Thread(() -> {
+            try {
+                SfuSignalingClient client = new SfuSignalingClient(this);
+                org.json.JSONObject resp = client.createRoom("Android lab", "screen_cast");
+                int janusId = resp.getJSONObject("room").getInt("janus_room_id");
+                runOnUiThread(() -> {
+                    EditText room = findViewById(R.id.edit_sfu_room_id);
+                    room.setText(String.valueOf(janusId));
+                    onLog("Created room " + janusId);
+                });
+            } catch (Exception e) {
+                runOnUiThread(() -> onError(e.getMessage()));
+            }
+        }).start();
+    }
+
+    private void publish() {
+        int roomId = parseInt(((EditText) findViewById(R.id.edit_sfu_room_id)).getText().toString(), 0);
+        if (roomId <= 0) {
+            Toast.makeText(this, R.string.sfu_lab_room_required, Toast.LENGTH_SHORT).show();
+            return;
+        }
+        if (!SfuAuthStore.hasSession(this)) {
+            Toast.makeText(this, R.string.sfu_lab_need_login, Toast.LENGTH_SHORT).show();
+            return;
+        }
+        session.publishCamera(roomId);
+    }
+
+    private void subscribe() {
+        int roomId = parseInt(((EditText) findViewById(R.id.edit_sfu_room_id)).getText().toString(), 0);
+        int feedId = parseInt(((EditText) findViewById(R.id.edit_sfu_feed_id)).getText().toString(), 0);
+        if (roomId <= 0 || feedId <= 0) {
+            Toast.makeText(this, R.string.sfu_lab_feed_required, Toast.LENGTH_SHORT).show();
+            return;
+        }
+        if (!SfuAuthStore.hasSession(this)) {
+            Toast.makeText(this, R.string.sfu_lab_need_login, Toast.LENGTH_SHORT).show();
+            return;
+        }
+        session.subscribe(roomId, feedId);
+    }
+
+    private void stopSession() {
+        if (session != null) {
+            session.stop();
+        }
+    }
+
+    private static int parseInt(String raw, int fallback) {
+        try {
+            return Integer.parseInt(raw.trim());
+        } catch (NumberFormatException e) {
+            return fallback;
+        }
+    }
+
+    @Override
+    public void onLog(String line) {
+        main.post(() -> {
+            logBuf.insert(0, line + '\n');
+            if (logBuf.length() > 4000) {
+                logBuf.setLength(4000);
+            }
+            logView.setText(logBuf.toString());
+        });
+    }
+
+    @Override
+    public void onPublisherId(int publisherId) {
+        main.post(() -> {
+            EditText feed = findViewById(R.id.edit_sfu_feed_id);
+            feed.setText(String.valueOf(publisherId));
+            onLog("Publisher feed id " + publisherId);
+        });
+    }
+
+    @Override
+    public void onError(String message) {
+        main.post(() -> {
+            Toast.makeText(this, message, Toast.LENGTH_LONG).show();
+            onLog("ERROR: " + message);
+        });
+    }
+}

app/src/main/java/com/foxx/androidcast/sfu/SfuLoginActivity.java

@@ -0,0 +1,46 @@
+package com.foxx.androidcast.sfu;
+
+import android.annotation.SuppressLint;
+import android.os.Bundle;
+import android.webkit.CookieManager;
+import android.webkit.WebResourceRequest;
+import android.webkit.WebView;
+import android.webkit.WebViewClient;
+
+import androidx.appcompat.app.AppCompatActivity;
+
+import com.foxx.androidcast.CastThemeHelper;
+import com.foxx.androidcast.R;
+import com.foxx.androidcast.network.BackendEndpoints;
+
+/** WebView login to issues console; cookies shared with SFU REST API. */
+public class SfuLoginActivity extends AppCompatActivity {
+    @SuppressLint("SetJavaScriptEnabled")
+    @Override
+    protected void onCreate(Bundle savedInstanceState) {
+        CastThemeHelper.applyTheme(this);
+        super.onCreate(savedInstanceState);
+        setContentView(R.layout.activity_sfu_login);
+        setTitle(R.string.sfu_lab_login);
+
+        WebView web = findViewById(R.id.sfu_login_webview);
+        CookieManager cm = CookieManager.getInstance();
+        cm.setAcceptCookie(true);
+        cm.setAcceptThirdPartyCookies(web, true);
+
+        web.getSettings().setJavaScriptEnabled(true);
+        web.setWebViewClient(new WebViewClient() {
+            @Override
+            public boolean shouldOverrideUrlLoading(WebView view, WebResourceRequest request) {
+                String url = request.getUrl().toString();
+                if (url.contains("/issues/") && !url.contains("login")) {
+                    setResult(RESULT_OK);
+                    finish();
+                    return true;
+                }
+                return false;
+            }
+        });
+        web.loadUrl(BackendEndpoints.ISSUES_BASE + "/");
+    }
+}

app/src/main/java/com/foxx/androidcast/sfu/SfuRelayGate.java

@@ -1,13 +1,16 @@
 package com.foxx.androidcast.sfu;
 
+import android.content.Context;
+
+import com.foxx.androidcast.AppPreferences;
 import com.foxx.androidcast.CastConfig;
 
 /**
- * Hidden gate for SFU / WebRTC relay experiments (post-alpha).
+ * Gate for SFU / WebRTC relay experiments (post-alpha).
- * Not exposed in release settings while {@link CastConfig#ALPHA_FEATURE_FREEZE} is on.
+ * Available when dev SFU relay is enabled, even under {@link CastConfig#ALPHA_FEATURE_FREEZE}.
  */
 public final class SfuRelayGate {
-    /** SFU preview enabled — Janus 1.4.1 deployed on cast02, signaling on cast01. */
+    /** SFU preview enabled — Janus deployed on cast02, signaling on cast01. */
     public static final boolean PREVIEW_ENABLED = true;
 
     /** REST base path for SFU rooms/join API (relative to app root). */
@@ -24,8 +27,15 @@ public final class SfuRelayGate {
 
     private SfuRelayGate() {}
 
-    public static boolean isAvailable() {
+    /** Dev/lab gate — does not require lifting global alpha freeze. */
-        return PREVIEW_ENABLED && !CastConfig.ALPHA_FEATURE_FREEZE;
+    public static boolean isAvailable(Context context) {
+        if (!PREVIEW_ENABLED) {
+            return false;
+        }
+        if (context != null && AppPreferences.isDevSfuRelayEnabled(context)) {
+            return true;
+        }
+        return !CastConfig.ALPHA_FEATURE_FREEZE;
     }
 
     /** Returns the full HTTP URL for the SFU health endpoint. */

app/src/main/java/com/foxx/androidcast/sfu/SfuRtcSession.java

@@ -0,0 +1,379 @@
+package com.foxx.androidcast.sfu;
+
+import android.content.Context;
+import android.util.Log;
+
+import org.json.JSONObject;
+import org.webrtc.AudioSource;
+import org.webrtc.AudioTrack;
+import org.webrtc.Camera2Enumerator;
+import org.webrtc.CameraEnumerator;
+import org.webrtc.CameraVideoCapturer;
+import org.webrtc.DefaultVideoDecoderFactory;
+import org.webrtc.DefaultVideoEncoderFactory;
+import org.webrtc.EglBase;
+import org.webrtc.IceCandidate;
+import org.webrtc.MediaConstraints;
+import org.webrtc.PeerConnection;
+import org.webrtc.PeerConnectionFactory;
+import org.webrtc.RtpReceiver;
+import org.webrtc.SdpObserver;
+import org.webrtc.SessionDescription;
+import org.webrtc.SurfaceTextureHelper;
+import org.webrtc.SurfaceViewRenderer;
+import org.webrtc.VideoSource;
+import org.webrtc.VideoTrack;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+
+/** libwebrtc publish/subscribe sessions against Janus VideoRoom via REST + WS trickle. */
+public final class SfuRtcSession implements PeerConnection.Observer {
+    public interface Callback {
+        void onLog(String line);
+
+        void onPublisherId(int publisherId);
+
+        void onError(String message);
+    }
+
+    private static final String TAG = "SfuRtcSession";
+    private static PeerConnectionFactory factory;
+    private static EglBase eglBase;
+
+    private final Context appContext;
+    private final ExecutorService executor = Executors.newSingleThreadExecutor();
+    private final Callback callback;
+    private PeerConnection peerConnection;
+    private JanusWebSocketClient janusWs;
+    private VideoSource videoSource;
+    private VideoTrack localVideo;
+    private CameraVideoCapturer capturer;
+    private SurfaceTextureHelper textureHelper;
+    private SurfaceViewRenderer localRenderer;
+    private SurfaceViewRenderer remoteRenderer;
+
+    public SfuRtcSession(Context context, Callback callback) {
+        this.appContext = context.getApplicationContext();
+        this.callback = callback;
+    }
+
+    public static synchronized void ensureFactory(Context context) {
+        if (factory != null) {
+            return;
+        }
+        PeerConnectionFactory.InitializationOptions init =
+                PeerConnectionFactory.InitializationOptions.builder(context)
+                        .setEnableInternalTracer(false)
+                        .createInitializationOptions();
+        PeerConnectionFactory.initialize(init);
+        eglBase = EglBase.create();
+        factory = PeerConnectionFactory.builder()
+                .setVideoEncoderFactory(new DefaultVideoEncoderFactory(
+                        eglBase.getEglBaseContext(), true, true))
+                .setVideoDecoderFactory(new DefaultVideoDecoderFactory(eglBase.getEglBaseContext()))
+                .createPeerConnectionFactory();
+    }
+
+    public static EglBase.Context eglContext() {
+        return eglBase != null ? eglBase.getEglBaseContext() : null;
+    }
+
+    public void attachLocalRenderer(SurfaceViewRenderer renderer) {
+        localRenderer = renderer;
+        if (localVideo != null) {
+            localVideo.addSink(renderer);
+        }
+    }
+
+    public void attachRemoteRenderer(SurfaceViewRenderer renderer) {
+        remoteRenderer = renderer;
+    }
+
+    public void publishCamera(int roomId) {
+        executor.execute(() -> {
+            try {
+                ensureFactory(appContext);
+                SfuSignalingClient api = new SfuSignalingClient(appContext);
+                startCameraCapture();
+                peerConnection = createPeerConnection();
+                if (localVideo != null) {
+                    peerConnection.addTrack(localVideo, List.of("stream"));
+                }
+                AudioSource audioSource = factory.createAudioSource(new MediaConstraints());
+                AudioTrack audioTrack = factory.createAudioTrack("audio0", audioSource);
+                peerConnection.addTrack(audioTrack, List.of("stream"));
+                SessionDescription offer = createOffer(peerConnection);
+                peerConnection.setLocalDescription(simpleSdpObserver("local"), offer);
+                JSONObject join = api.joinPublisher(roomId, offer.type.canonicalForm(), offer.description);
+                applyJoinResponse(join);
+                log("Publisher joined room " + roomId);
+            } catch (Exception e) {
+                Log.e(TAG, "publish", e);
+                callback.onError(e.getMessage() != null ? e.getMessage() : "publish failed");
+            }
+        });
+    }
+
+    public void subscribe(int roomId, int feedId) {
+        executor.execute(() -> {
+            try {
+                ensureFactory(appContext);
+                SfuSignalingClient api = new SfuSignalingClient(appContext);
+                peerConnection = createPeerConnection();
+                peerConnection.addTransceiver(org.webrtc.MediaStreamTrack.MediaType.MEDIA_TYPE_VIDEO,
+                        new org.webrtc.RtpTransceiver.RtpTransceiverInit(
+                                org.webrtc.RtpTransceiver.RtpTransceiverDirection.RECV_ONLY));
+                peerConnection.addTransceiver(org.webrtc.MediaStreamTrack.MediaType.MEDIA_TYPE_AUDIO,
+                        new org.webrtc.RtpTransceiver.RtpTransceiverInit(
+                                org.webrtc.RtpTransceiver.RtpTransceiverDirection.RECV_ONLY));
+                SessionDescription offer = createOffer(peerConnection);
+                peerConnection.setLocalDescription(simpleSdpObserver("local"), offer);
+                JSONObject join = api.joinSubscriber(roomId, feedId, offer.type.canonicalForm(), offer.description);
+                applyJoinResponse(join);
+                log("Subscriber watching feed " + feedId);
+            } catch (Exception e) {
+                Log.e(TAG, "subscribe", e);
+                callback.onError(e.getMessage() != null ? e.getMessage() : "subscribe failed");
+            }
+        });
+    }
+
+    public void stop() {
+        executor.execute(() -> {
+            if (janusWs != null) {
+                janusWs.close();
+                janusWs = null;
+            }
+            if (capturer != null) {
+                try {
+                    capturer.stopCapture();
+                } catch (InterruptedException ignored) {
+                    Thread.currentThread().interrupt();
+                }
+                capturer.dispose();
+                capturer = null;
+            }
+            if (textureHelper != null) {
+                textureHelper.dispose();
+                textureHelper = null;
+            }
+            if (videoSource != null) {
+                videoSource.dispose();
+                videoSource = null;
+            }
+            if (localVideo != null) {
+                localVideo.dispose();
+                localVideo = null;
+            }
+            if (peerConnection != null) {
+                peerConnection.close();
+                peerConnection = null;
+            }
+        });
+    }
+
+    private void applyJoinResponse(JSONObject join) throws org.json.JSONException {
+        long sessionId = join.getLong("session_id");
+        long handleId = join.getLong("handle_id");
+        if (join.has("publisher_id") && !join.isNull("publisher_id")) {
+            callback.onPublisherId(join.getInt("publisher_id"));
+        }
+        JSONObject jsep = join.getJSONObject("jsep");
+        SessionDescription answer = new SessionDescription(
+                SessionDescription.Type.fromCanonicalForm(jsep.getString("type")),
+                jsep.getString("sdp"));
+        peerConnection.setRemoteDescription(simpleSdpObserver("remote"), answer);
+        janusWs = new JanusWebSocketClient();
+        janusWs.connect(sessionId, handleId, new JanusWebSocketClient.Listener() {
+            @Override
+            public void onTrickle(JSONObject candidate) {
+                if (candidate.optBoolean("completed")) {
+                    return;
+                }
+                IceCandidate ice = new IceCandidate(
+                        candidate.optString("sdpMid"),
+                        candidate.optInt("sdpMLineIndex"),
+                        candidate.optString("candidate"));
+                peerConnection.addIceCandidate(ice);
+            }
+
+            @Override
+            public void onFailure(String message) {
+                callback.onError(message);
+            }
+        });
+    }
+
+    private PeerConnection createPeerConnection() {
+        List<PeerConnection.IceServer> ice = new ArrayList<>();
+        ice.add(PeerConnection.IceServer.builder("stun:stun.l.google.com:19302").createIceServer());
+        ice.add(PeerConnection.IceServer.builder("stun:stun1.l.google.com:19302").createIceServer());
+        PeerConnection.RTCConfiguration config = new PeerConnection.RTCConfiguration(ice);
+        config.sdpSemantics = PeerConnection.SdpSemantics.UNIFIED_PLAN;
+        PeerConnection pc = factory.createPeerConnection(config, this);
+        if (pc == null) {
+            throw new IllegalStateException("PeerConnection unavailable");
+        }
+        return pc;
+    }
+
+    private void startCameraCapture() {
+        CameraEnumerator enumerator = new Camera2Enumerator(appContext);
+        String device = null;
+        for (String name : enumerator.getDeviceNames()) {
+            if (enumerator.isFrontFacing(name)) {
+                device = name;
+                break;
+            }
+        }
+        if (device == null && enumerator.getDeviceNames().length > 0) {
+            device = enumerator.getDeviceNames()[0];
+        }
+        if (device == null) {
+            throw new IllegalStateException("No camera");
+        }
+        capturer = enumerator.createCapturer(device, null);
+        textureHelper = SurfaceTextureHelper.create("SfuCap", eglBase.getEglBaseContext());
+        videoSource = factory.createVideoSource(capturer.isScreencast());
+        capturer.initialize(textureHelper, appContext, videoSource.getCapturerObserver());
+        capturer.startCapture(1280, 720, 30);
+        localVideo = factory.createVideoTrack("video0", videoSource);
+        if (localRenderer != null) {
+            localVideo.addSink(localRenderer);
+        }
+    }
+
+    private SessionDescription createOffer(PeerConnection pc) {
+        final SessionDescription[] holder = new SessionDescription[1];
+        final Exception[] error = new Exception[1];
+        MediaConstraints mc = new MediaConstraints();
+        pc.createOffer(new SdpObserver() {
+            @Override
+            public void onCreateSuccess(SessionDescription sessionDescription) {
+                holder[0] = sessionDescription;
+                synchronized (holder) {
+                    holder.notifyAll();
+                }
+            }
+
+            @Override
+            public void onCreateFailure(String s) {
+                error[0] = new IllegalStateException(s);
+                synchronized (holder) {
+                    holder.notifyAll();
+                }
+            }
+
+            @Override
+            public void onSetSuccess() {}
+
+            @Override
+            public void onSetFailure(String s) {}
+        }, mc);
+        synchronized (holder) {
+            while (holder[0] == null && error[0] == null) {
+                try {
+                    holder.wait(15_000);
+                } catch (InterruptedException e) {
+                    Thread.currentThread().interrupt();
+                    throw new IllegalStateException("offer interrupted");
+                }
+            }
+        }
+        if (error[0] != null) {
+            throw new IllegalStateException(error[0].getMessage());
+        }
+        if (holder[0] == null) {
+            throw new IllegalStateException("offer timeout");
+        }
+        return holder[0];
+    }
+
+    private SdpObserver simpleSdpObserver(String label) {
+        return new SdpObserver() {
+            @Override
+            public void onCreateSuccess(SessionDescription sessionDescription) {}
+
+            @Override
+            public void onSetSuccess() {
+                log(label + " SDP set");
+            }
+
+            @Override
+            public void onCreateFailure(String s) {
+                callback.onError(label + " create: " + s);
+            }
+
+            @Override
+            public void onSetFailure(String s) {
+                callback.onError(label + " set: " + s);
+            }
+        };
+    }
+
+    private void log(String msg) {
+        callback.onLog(msg);
+    }
+
+    @Override
+    public void onIceCandidate(IceCandidate iceCandidate) {
+        if (janusWs == null) {
+            return;
+        }
+        try {
+            JSONObject c = new JSONObject();
+            c.put("candidate", iceCandidate.sdp);
+            c.put("sdpMid", iceCandidate.sdpMid);
+            c.put("sdpMLineIndex", iceCandidate.sdpMLineIndex);
+            janusWs.sendTrickle(c);
+        } catch (org.json.JSONException e) {
+            Log.w(TAG, "local trickle", e);
+        }
+    }
+
+    @Override
+    public void onIceCandidatesRemoved(IceCandidate[] iceCandidates) {}
+
+    @Override
+    public void onAddStream(org.webrtc.MediaStream mediaStream) {}
+
+    @Override
+    public void onSignalingChange(PeerConnection.SignalingState signalingState) {}
+
+    @Override
+    public void onIceConnectionChange(PeerConnection.IceConnectionState iceConnectionState) {
+        log("ICE " + iceConnectionState);
+    }
+
+    @Override
+    public void onIceConnectionReceivingChange(boolean b) {}
+
+    @Override
+    public void onIceGatheringChange(PeerConnection.IceGatheringState iceGatheringState) {
+        if (iceGatheringState == PeerConnection.IceGatheringState.COMPLETE && janusWs != null) {
+            try {
+                janusWs.sendTrickle(new JSONObject().put("completed", true));
+            } catch (org.json.JSONException ignored) {}
+        }
+    }
+
+    @Override
+    public void onRemoveStream(org.webrtc.MediaStream mediaStream) {}
+
+    @Override
+    public void onDataChannel(org.webrtc.DataChannel dataChannel) {}
+
+    @Override
+    public void onRenegotiationNeeded() {}
+
+    @Override
+    public void onAddTrack(RtpReceiver rtpReceiver, org.webrtc.MediaStream[] mediaStreams) {
+        org.webrtc.MediaStreamTrack track = rtpReceiver.track();
+        if (track instanceof VideoTrack && remoteRenderer != null) {
+            ((VideoTrack) track).addSink(remoteRenderer);
+        }
+    }
+}

app/src/main/java/com/foxx/androidcast/sfu/SfuSignalingClient.java

@@ -0,0 +1,128 @@
+package com.foxx.androidcast.sfu;
+
+import android.content.Context;
+
+import org.json.JSONObject;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.net.HttpURLConnection;
+import java.net.URL;
+import java.nio.charset.StandardCharsets;
+
+import okhttp3.MediaType;
+import okhttp3.OkHttpClient;
+import okhttp3.Request;
+import okhttp3.RequestBody;
+import okhttp3.Response;
+
+/** REST client for ac-ms-sfu-signaling join/rooms API. */
+public final class SfuSignalingClient {
+    private static final MediaType JSON = MediaType.get("application/json; charset=utf-8");
+    private static final int TIMEOUT_MS = 30_000;
+
+    private final OkHttpClient http;
+    private final String cookieHeader;
+
+    public SfuSignalingClient(Context context) {
+        this.http = new OkHttpClient.Builder()
+                .connectTimeout(TIMEOUT_MS, java.util.concurrent.TimeUnit.MILLISECONDS)
+                .readTimeout(TIMEOUT_MS, java.util.concurrent.TimeUnit.MILLISECONDS)
+                .build();
+        this.cookieHeader = SfuAuthStore.cookieHeader(context);
+    }
+
+    public JSONObject health() throws IOException {
+        HttpURLConnection conn = (HttpURLConnection) new URL(SfuEndpoints.healthUrl()).openConnection();
+        conn.setConnectTimeout(TIMEOUT_MS);
+        conn.setReadTimeout(TIMEOUT_MS);
+        conn.setRequestMethod("GET");
+        int code = conn.getResponseCode();
+        InputStream in = code >= 400 ? conn.getErrorStream() : conn.getInputStream();
+        String body = readStream(in);
+        conn.disconnect();
+        try {
+            JSONObject json = new JSONObject(body);
+            if (code >= 400) {
+                throw new IOException(json.optString("error", "HTTP " + code));
+            }
+            return json;
+        } catch (org.json.JSONException e) {
+            throw new IOException(e);
+        }
+    }
+
+    public JSONObject createRoom(String name, String purpose) throws IOException {
+        JSONObject body = new JSONObject();
+        try {
+            body.put("name", name);
+            body.put("purpose", purpose != null ? purpose : "screen_cast");
+        } catch (org.json.JSONException e) {
+            throw new IOException(e);
+        }
+        return postJson(SfuEndpoints.roomsUrl(), body);
+    }
+
+    public JSONObject joinPublisher(int roomId, String offerType, String offerSdp) throws IOException {
+        return join(roomId, "publisher", 0, offerType, offerSdp);
+    }
+
+    public JSONObject joinSubscriber(int roomId, int feedId, String offerType, String offerSdp) throws IOException {
+        return join(roomId, "subscriber", feedId, offerType, offerSdp);
+    }
+
+    private JSONObject join(int roomId, String role, int feedId, String offerType, String offerSdp)
+            throws IOException {
+        JSONObject body = new JSONObject();
+        JSONObject jsep = new JSONObject();
+        try {
+            jsep.put("type", offerType);
+            jsep.put("sdp", offerSdp);
+            body.put("room_id", roomId);
+            body.put("role", role);
+            if (feedId > 0) {
+                body.put("feed_id", feedId);
+            }
+            body.put("jsep", jsep);
+        } catch (org.json.JSONException e) {
+            throw new IOException(e);
+        }
+        return postJson(SfuEndpoints.joinUrl(), body);
+    }
+
+    private JSONObject postJson(String url, JSONObject body) throws IOException {
+        Request.Builder req = new Request.Builder()
+                .url(url)
+                .post(RequestBody.create(body.toString(), JSON));
+        if (cookieHeader != null && !cookieHeader.isEmpty()) {
+            req.header("Cookie", cookieHeader);
+        }
+        try (Response resp = http.newCall(req.build()).execute()) {
+            String text = resp.body() != null ? resp.body().string() : "";
+            JSONObject json = text.isEmpty() ? new JSONObject() : new JSONObject(text);
+            if (!resp.isSuccessful()) {
+                throw new IOException(json.optString("error", "HTTP " + resp.code()));
+            }
+            if (!json.optBoolean("ok", false)) {
+                throw new IOException(json.optString("error", "request failed"));
+            }
+            return json;
+        } catch (org.json.JSONException e) {
+            throw new IOException(e);
+        }
+    }
+
+    private static String readStream(InputStream in) throws IOException {
+        if (in == null) {
+            return "";
+        }
+        byte[] buf = new byte[4096];
+        StringBuilder sb = new StringBuilder();
+        int n;
+        while ((n = in.read(buf)) >= 0) {
+            sb.append(new String(buf, 0, n, StandardCharsets.UTF_8));
+        }
+        in.close();
+        return sb.toString();
+    }
+}

app/src/main/res/layout/activity_dev_settings_panel.xml

@@ -417,6 +417,20 @@
             android:layout_marginTop="12dp"
             android:text="@string/dev_usb_tether_transport" />
 
+        <CheckBox
+            android:id="@+id/check_dev_sfu_relay"
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:layout_marginTop="8dp"
+            android:text="@string/dev_sfu_relay" />
+
+        <Button
+            android:id="@+id/btn_open_sfu_lab"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:layout_marginTop="4dp"
+            android:text="@string/dev_open_sfu_lab" />
+
         <TextView
             android:layout_width="match_parent"
             android:layout_height="wrap_content"

app/src/main/res/layout/activity_sfu_lab.xml

@@ -0,0 +1,114 @@
+<?xml version="1.0" encoding="utf-8"?>
+<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    android:padding="16dp">
+
+    <LinearLayout
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:orientation="vertical">
+
+        <TextView
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:text="@string/sfu_lab_title"
+            android:textAppearance="?attr/textAppearanceHeadline6" />
+
+        <TextView
+            android:id="@+id/text_sfu_lab_status"
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:layout_marginTop="8dp"
+            android:textAppearance="?attr/textAppearanceBody2" />
+
+        <Button
+            android:id="@+id/btn_sfu_login"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:layout_marginTop="8dp"
+            android:text="@string/sfu_lab_login" />
+
+        <EditText
+            android:id="@+id/edit_sfu_room_id"
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:layout_marginTop="12dp"
+            android:hint="@string/sfu_lab_room_id"
+            android:inputType="number" />
+
+        <EditText
+            android:id="@+id/edit_sfu_feed_id"
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:hint="@string/sfu_lab_feed_id"
+            android:inputType="number" />
+
+        <LinearLayout
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:layout_marginTop="8dp"
+            android:orientation="horizontal">
+
+            <Button
+                android:id="@+id/btn_sfu_create_room"
+                android:layout_width="0dp"
+                android:layout_height="wrap_content"
+                android:layout_weight="1"
+                android:text="@string/sfu_lab_create_room" />
+
+            <Button
+                android:id="@+id/btn_sfu_publish"
+                android:layout_width="0dp"
+                android:layout_height="wrap_content"
+                android:layout_marginStart="8dp"
+                android:layout_weight="1"
+                android:text="@string/sfu_lab_publish" />
+        </LinearLayout>
+
+        <Button
+            android:id="@+id/btn_sfu_subscribe"
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:layout_marginTop="8dp"
+            android:text="@string/sfu_lab_subscribe" />
+
+        <Button
+            android:id="@+id/btn_sfu_stop"
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:text="@string/sfu_lab_stop" />
+
+        <TextView
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:layout_marginTop="16dp"
+            android:text="@string/sfu_lab_local" />
+
+        <org.webrtc.SurfaceViewRenderer
+            android:id="@+id/sfu_local_video"
+            android:layout_width="match_parent"
+            android:layout_height="180dp"
+            android:layout_marginTop="4dp" />
+
+        <TextView
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:layout_marginTop="12dp"
+            android:text="@string/sfu_lab_remote" />
+
+        <org.webrtc.SurfaceViewRenderer
+            android:id="@+id/sfu_remote_video"
+            android:layout_width="match_parent"
+            android:layout_height="180dp"
+            android:layout_marginTop="4dp" />
+
+        <TextView
+            android:id="@+id/text_sfu_log"
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:layout_marginTop="12dp"
+            android:fontFamily="monospace"
+            android:textAppearance="?attr/textAppearanceCaption" />
+    </LinearLayout>
+</ScrollView>

app/src/main/res/layout/activity_sfu_login.xml

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="utf-8"?>
+<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent">
+
+    <WebView
+        android:id="@+id/sfu_login_webview"
+        android:layout_width="match_parent"
+        android:layout_height="match_parent" />
+</FrameLayout>

app/src/main/res/values/strings.xml

@@ -29,7 +29,7 @@
     <string name="transport_udp">UDP (default, best effort)</string>
     <string name="transport_tcp">TCP (reliable fallback)</string>
     <string name="transport_quic">QUIC experimental (Cronet)</string>
-    <string name="transport_webrtc">WebRTC (stub, future)</string>
+    <string name="transport_webrtc">WebRTC / SFU (dev lab)</string>
     <string name="capture_calibration_test">Calibration test pattern</string>
     <string name="capture_camera">Camera (rear Camera2)</string>
     <string name="capture_camera_unavailable">Camera source (requires Android 10+)</string>
@@ -265,6 +265,23 @@
     <string name="dev_wired_display_hint">Wired HDMI uses the OS display stack, not the cast protocol. If no second screen appears in system Display settings, adapters cannot be fixed in-app. See docs/USB_HDMI_CAST.md.</string>
     <string name="dev_external_capture_policy">External display capture policy (future)</string>
     <string name="dev_usb_tether_transport">Show USB-tether transport in cast settings (stub, roadmap E)</string>
+    <string name="dev_sfu_relay">Enable Janus SFU relay lab (libwebrtc M1)</string>
+    <string name="dev_open_sfu_lab">Open SFU lab</string>
+    <string name="sfu_lab_title">SFU lab</string>
+    <string name="sfu_lab_unavailable">SFU lab disabled — enable in developer settings</string>
+    <string name="sfu_lab_login">Sign in (issues console)</string>
+    <string name="sfu_lab_authed">Signed in — SFU API ready</string>
+    <string name="sfu_lab_need_login">Sign in required for room create/join</string>
+    <string name="sfu_lab_room_id">Janus room id</string>
+    <string name="sfu_lab_feed_id">Publisher feed id</string>
+    <string name="sfu_lab_create_room">Create room</string>
+    <string name="sfu_lab_publish">Publish camera</string>
+    <string name="sfu_lab_subscribe">Subscribe</string>
+    <string name="sfu_lab_stop">Stop</string>
+    <string name="sfu_lab_local">Local preview</string>
+    <string name="sfu_lab_remote">Remote viewer</string>
+    <string name="sfu_lab_room_required">Enter Janus room id</string>
+    <string name="sfu_lab_feed_required">Enter room id and publisher feed id</string>
     <string name="wired_display_detected_hint">External display detected — use system mirror or Wi‑Fi cast to receiver</string>
     <string name="transport_usb_tether">USB tether (experimental)</string>
     <string name="dev_adb_wifi_section">ADB over Wi‑Fi (debug)</string>

app/src/test/java/com/foxx/androidcast/sfu/SfuEndpointsTest.java

@@ -0,0 +1,28 @@
+package com.foxx.androidcast.sfu;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+public class SfuEndpointsTest {
+
+    @Test
+    public void apiBase_usesAppsHost() {
+        assertTrue(SfuEndpoints.apiBase().startsWith("https://"));
+        assertTrue(SfuEndpoints.apiBase().contains("apps.f0xx.org"));
+        assertTrue(SfuEndpoints.apiBase().endsWith("/app/androidcast_project/sfu/api"));
+    }
+
+    @Test
+    public void webSocket_isSecure() {
+        assertTrue(SfuEndpoints.webSocketUrl().startsWith("wss://"));
+        assertTrue(SfuEndpoints.webSocketUrl().contains("/sfu/ws"));
+    }
+
+    @Test
+    public void joinUrl_underApiBase() {
+        assertEquals(SfuEndpoints.apiBase() + "/join", SfuEndpoints.joinUrl());
+    }
+}

app/src/test/java/com/foxx/androidcast/sfu/SfuRelayGateTest.java

@@ -1,14 +1,52 @@
 package com.foxx.androidcast.sfu;
 
-import static org.junit.Assert.*;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
 
+import android.content.Context;
+
+import com.foxx.androidcast.AppPreferences;
+import com.foxx.androidcast.CastConfig;
+
+import org.junit.After;
+import org.junit.Before;
 import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.robolectric.RobolectricTestRunner;
+import org.robolectric.RuntimeEnvironment;
 
+@RunWith(RobolectricTestRunner.class)
 public class SfuRelayGateTest {
+    private Context context;
+
+    @Before
+    public void setUp() {
+        context = RuntimeEnvironment.getApplication();
+        AppPreferences.setDevSfuRelayEnabled(context, false);
+    }
+
+    @After
+    public void tearDown() {
+        AppPreferences.setDevSfuRelayEnabled(context, false);
+    }
 
     @Test
     public void previewEnabled_isTrue() {
-        assertTrue("SfuRelayGate.PREVIEW_ENABLED should be true", SfuRelayGate.PREVIEW_ENABLED);
+        assertTrue(SfuRelayGate.PREVIEW_ENABLED);
+    }
+
+    @Test
+    public void isAvailable_falseWhenDevOffAndAlphaFreeze() {
+        AppPreferences.setDevSfuRelayEnabled(context, false);
+        assertTrue(CastConfig.ALPHA_FEATURE_FREEZE);
+        assertFalse(SfuRelayGate.isAvailable(context));
+    }
+
+    @Test
+    public void isAvailable_trueWhenDevSfuOn() {
+        AppPreferences.setDevSfuRelayEnabled(context, true);
+        assertTrue(SfuRelayGate.isAvailable(context));
     }
 
     @Test
@@ -41,7 +79,7 @@ public class SfuRelayGateTest {
     @Test
     public void healthUrl_trailingSlash() {
         String url = SfuRelayGate.healthUrl("https://apps.f0xx.org/");
-        /* Path should not have a double-slash before /app/androidcast_project */
+        assertFalse(url.contains("org//app"));
-        assertFalse("Double-slash found in path", url.contains("org//app"));
     }
 }
+