Activate iOS audio session before stereo input selection

clients/apple/VoiceCat.iOS/IosAudioRouter.cs

@@ -147,8 +147,9 @@ internal sealed class IosAudioRouter
                 : BluetoothMode == IosBluetoothMode.BuiltInMicA2dp ? AVAudioSessionMode.VideoRecording : AVAudioSessionMode.VoiceChat;
             if (!session.SetCategory(AVAudioSessionCategory.PlayAndRecord, mode, options, out NSError? categoryError)) throw new InvalidOperationException(categoryError?.LocalizedDescription ?? "Could not configure the iOS audio session.");
             session.SetPreferredSampleRate(48_000, out _); session.SetPreferredIOBufferDuration(0.02, out _);
-            if (configureInput) ApplyInputSelection(session);
             if (!session.SetActive(true, AVAudioSessionSetActiveOptions.NotifyOthersOnDeactivation, out NSError? activeError)) throw new InvalidOperationException(activeError?.LocalizedDescription ?? "Could not activate the iOS audio session.");
+            // Apple requires an active session before selecting a preferred input or data source.
+            if (configureInput) ApplyInputSelection(session);
             Console.Error.WriteLine($"VC_ROUTE preset={Preset} requestedCh={CaptureChannels} sessionCh={session.InputNumberOfChannels} " +
                 $"preferred={session.PreferredInput?.PortName ?? "default"} dataSource={session.InputDataSource?.DataSourceName ?? "default"} " +
                 $"pattern={session.InputDataSource?.SelectedPolarPattern.ToString() ?? "default"}");
@@ -172,6 +173,7 @@ internal sealed class IosAudioRouter
         AVAudioSessionPortDescription? port = session.AvailableInputs?.FirstOrDefault(value => value.UID == SelectedInputId);
         if (CaptureChannels == 2) port ??= session.AvailableInputs?.FirstOrDefault(value => value.PortType == AVAudioSession.PortBuiltInMic);
         if (port is null) { if (CaptureChannels == 1 && stereoApplied) ClearStereo(session); return; }
+        if (!session.SetPreferredInput(port, out NSError? inputError)) throw new InvalidOperationException(inputError?.LocalizedDescription ?? "Could not select the microphone input.");
         if (CaptureChannels == 2)
         {
             // Polar-pattern discovery alone is insufficient on current iPhones: until a stereo
@@ -195,13 +197,11 @@ internal sealed class IosAudioRouter
                 !source.SetPreferredPolarPattern(SelectedPolarPattern, out NSError? patternError))
                 throw new InvalidOperationException(patternError?.LocalizedDescription ?? "Could not select the microphone polar pattern.");
         }
-        if (!session.SetPreferredInput(port, out NSError? inputError)) throw new InvalidOperationException(inputError?.LocalizedDescription ?? "Could not select the microphone input.");
         // The working Swift client deliberately does not call
         // SetPreferredInputNumberOfChannels: doing so disrupts stereo + A2DP routing. The stereo
         // capsule and polar pattern above cause the input node to expose its two-channel format.
-        if (CaptureChannels == 2 && source is not null &&
-            !session.SetInputDataSource(source, out NSError? sourceError))
-            throw new InvalidOperationException(sourceError?.LocalizedDescription ?? "Could not activate the stereo microphone source.");
+        // A port preference is enough. SetInputDataSource only accepts a member of the *current*
+        // port's InputDataSources, which can still be a different route after SetPreferredInput.
         Console.Error.WriteLine($"VC_ROUTE_SELECT port={port.PortName} source={source?.DataSourceName ?? "none"} " +
             $"stereoPattern={source is not null && SupportsStereoPolarPattern(source)} " +
             $"patterns={string.Join(',', source?.SupportedPolarPatterns?.Select(value => value.ToString()) ?? [])}");

clients/apple/VoiceCat.iOS/SimulatorSmoke.cs

@@ -32,6 +32,8 @@ internal static class SimulatorSmoke
                     model.UpsertProfile(profile, parts[2]);
                 }
                 model.Load();
+                if (Environment.GetEnvironmentVariable("VOICECAT_SIM_SMOKE_MODE") == "stereo")
+                    IosAudioRouter.Shared.SelectPreset(IosAudioPreset.StereoMicrophone);
                 profile = model.Profiles.Single(value => value.Id == id);
                 Console.Error.WriteLine("VC_SIM phase=connect");
                 await model.ConnectAsync(profile);