Reduce Linux setup ambiguity and surface desktop input/message failures honestly

Clarify ONNX Runtime guidance with direct-open install hints, restore desktop WebRTC VAD visibility, map mouse side buttons through focused PTT capture/runtime paths, and wait for server acks before showing chat sends as successful.

Constraint: Linux release UX must stay functional when ONNX Runtime is optional and GNOME portal availability varies
Rejected: Keep desktop VAD locked to Silero only | misleads users when ONNX Runtime is skipped
Confidence: medium
Scope-risk: moderate
Directive: Preserve the protocol send-ack wait path for chat so UI success always tracks real server acceptance
Tested: flutter analyze lib/main.dart lib/widgets/chat_views.dart lib/widgets/input_dialogs.dart lib/widgets/startup_dependency_screen.dart; flutter test test/widgets/input_dialogs_test.dart test/widgets/chat_views_test.dart test/services/startup_dependency_check_test.dart test/widgets/startup_dependency_screen_test.dart test/widgets/voice_settings_controls_test.dart test/widgets/audio_processing_config_state_test.dart; cargo test -p chanora_protocol --lib; cargo test -p chanora_audio ptt_backends --lib
Not-tested: Live manual GNOME portal rebind/global PTT on a real desktop session; observer-bot chat against a live server after the sender-name fallback change

apps/chanora_flutter/test/widgets/audio_processing_config_state_test.dart

@@ -31,14 +31,14 @@ void main() {
     expect(state.agcEnabled, isTrue);
   });
 
-  test('normalizes desktop VAD backend to Silero', () {
+  test('desktop VAD normalization keeps explicit WebRTC selections', () {
     expect(
       normalizedVadBackend(
         rust.BridgeVadBackend.webrtcVad,
         isWindows: true,
         isLinux: false,
       ),
-      rust.BridgeVadBackend.sileroOnnx,
+      rust.BridgeVadBackend.webrtcVad,
     );
     expect(
       normalizedVadBackend(
@@ -46,6 +46,14 @@ void main() {
         isWindows: false,
         isLinux: true,
       ),
+      rust.BridgeVadBackend.webrtcVad,
+    );
+    expect(
+      normalizedVadBackend(
+        rust.BridgeVadBackend.energyDebug,
+        isWindows: true,
+        isLinux: false,
+      ),
       rust.BridgeVadBackend.sileroOnnx,
     );
   });
@@ -103,6 +111,7 @@ void main() {
 
   test('builds Windows/Linux software WebRTC APM config consistently', () {
     final state = AudioProcessingConfigState.fromConfig(baseConfig)
+      ..vadBackend = rust.BridgeVadBackend.webrtcVad
       ..nsEnabled = true
       ..aecEnabled = false
       ..agcEnabled = true;
@@ -127,7 +136,7 @@ void main() {
 
     for (final config in [windowsConfig, linuxConfig]) {
       expect(config.processingBackend, rust.BridgeAudioBackend.webrtcApm);
-      expect(config.vadBackend, rust.BridgeVadBackend.sileroOnnx);
+      expect(config.vadBackend, rust.BridgeVadBackend.webrtcVad);
       expect(config.aec, rust.BridgeEffectOwner.off);
       expect(config.ns, rust.BridgeEffectOwner.webrtcApm);
       expect(config.agc, rust.BridgeEffectOwner.webrtcApm);

apps/chanora_flutter/test/widgets/input_dialogs_test.dart

@@ -0,0 +1,41 @@
+import 'package:flutter/services.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import 'package:chanora_flutter/widgets/input_dialogs.dart';
+
+void main() {
+  test('browser back and forward logical keys map to mouse side bindings', () {
+    expect(
+      pttMouseSideButtonPlatformKeyForLogicalKey(
+        LogicalKeyboardKey.browserBack,
+      ),
+      'mouse-side-button:8',
+    );
+    expect(
+      pttMouseSideButtonPlatformKeyForLogicalKey(LogicalKeyboardKey.goBack),
+      'mouse-side-button:8',
+    );
+    expect(
+      pttMouseSideButtonPlatformKeyForLogicalKey(
+        LogicalKeyboardKey.browserForward,
+      ),
+      'mouse-side-button:16',
+    );
+  });
+
+  test('pointer button bitmasks map to mouse side bindings', () {
+    expect(
+      pttMouseSideButtonPlatformKeyForButtons(0x08),
+      'mouse-side-button:8',
+    );
+    expect(
+      pttMouseSideButtonPlatformKeyForButtons(0x10),
+      'mouse-side-button:16',
+    );
+    expect(
+      pttMouseSideButtonPlatformKeyForButtons(0x18),
+      'mouse-side-button:8',
+    );
+    expect(pttMouseSideButtonPlatformKeyForButtons(0x00), isNull);
+  });
+}

apps/chanora_flutter/test/widgets/startup_dependency_screen_test.dart

@@ -0,0 +1,67 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import 'package:chanora_flutter/services/startup_dependency_check.dart';
+import 'package:chanora_flutter/widgets/startup_dependency_screen.dart';
+
+void main() {
+  testWidgets('startup gate shows install-help screen and can continue', (
+    tester,
+  ) async {
+    tester.view.physicalSize = const Size(1200, 1800);
+    tester.view.devicePixelRatio = 1.0;
+    addTearDown(tester.view.resetPhysicalSize);
+    addTearDown(tester.view.resetDevicePixelRatio);
+
+    final result = StartupDependencyCheckResult(
+      platformLabel: 'Fedora',
+      issues: const [
+        StartupDependencyIssue(
+          id: 'linux-sdl2-runtime',
+          title: 'SDL2 runtime is missing',
+          summary: 'Audio playback needs SDL2.',
+          details: ['Install SDL2 and recheck.'],
+          severity: StartupDependencySeverity.required,
+          installHints: [
+            StartupInstallHint(
+              label: 'Release downloads',
+              command: 'https://github.com/microsoft/onnxruntime/releases',
+            ),
+            StartupInstallHint(
+              label: 'Fedora',
+              command: 'sudo dnf install SDL2',
+            ),
+          ],
+        ),
+      ],
+    );
+    final loggedResults = <StartupDependencyCheckResult>[];
+
+    await tester.pumpWidget(
+      MaterialApp(
+        home: StartupDependencyGate(
+          checker: () async => result,
+          logger: (value) async {
+            loggedResults.add(value);
+          },
+          child: const Scaffold(body: Text('ready')),
+        ),
+      ),
+    );
+
+    await tester.pumpAndSettle();
+
+    expect(find.text('Finish Linux setup'), findsOneWidget);
+    expect(find.text('SDL2 runtime is missing'), findsOneWidget);
+    expect(find.text('Continue with limited mode'), findsOneWidget);
+    expect(find.text('Open'), findsOneWidget);
+    expect(find.text('Copy'), findsOneWidget);
+    expect(loggedResults, [result]);
+
+    await tester.ensureVisible(find.text('Continue with limited mode'));
+    await tester.tap(find.text('Continue with limited mode'));
+    await tester.pumpAndSettle();
+
+    expect(find.text('ready'), findsOneWidget);
+  });
+}

apps/chanora_flutter/test/widgets/voice_settings_controls_test.dart

@@ -24,8 +24,9 @@ void main() {
     ]);
   });
 
-  test('desktop VAD segments expose Silero as the primary backend', () {
+  test('desktop VAD segments expose both Silero and WebRTC', () {
     expect(desktopVadBackendSegments.map((s) => s.value), [
+      rust.BridgeVadBackend.webrtcVad,
       rust.BridgeVadBackend.sileroOnnx,
     ]);
   });