Address PR #282 review feedback: exit codes, type splitting, structured args

- AdbRunner: check exit codes consistently in ListDevicesAsync, WaitForDeviceAsync, StopEmulatorAsync
- AdbRunner: bare catch {} → catch (Exception) in GetEmulatorAvdNameAsync
- AdbDeviceInfo.cs: split 3 public types into separate files (AdbDeviceType.cs, AdbDeviceStatus.cs)
- EnvironmentVariableNames: add AndroidAvdHome constant, use in AvdManagerRunner
- EmulatorRunner.StartAvd: additionalArgs string? → IEnumerable<string>? for proper arg separation
- EmulatorRunner.StartAvd: set RedirectStandardOutput/Error=false to prevent pipe deadlock

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: rmarinho

src/Xamarin.Android.Tools.AndroidSdk/EnvironmentVariableNames.cs

@@ -46,5 +46,11 @@ internal static class EnvironmentVariableNames
 		/// (AVDs, preferences, etc.). Defaults to $HOME/.android.
 		/// </summary>
 		public const string AndroidUserHome = "ANDROID_USER_HOME";
+
+		/// <summary>
+		/// Overrides the AVD storage directory.
+		/// Defaults to $ANDROID_USER_HOME/avd or $HOME/.android/avd.
+		/// </summary>
+		public const string AndroidAvdHome = "ANDROID_AVD_HOME";
 	}
 }

src/Xamarin.Android.Tools.AndroidSdk/Models/AdbDeviceInfo.cs

@@ -3,28 +3,6 @@
 
 namespace Xamarin.Android.Tools;
 
-/// <summary>
-/// Represents the type of an Android device.
-/// </summary>
-public enum AdbDeviceType
-{
-	Device,
-	Emulator
-}
-
-/// <summary>
-/// Represents the status of an Android device.
-/// </summary>
-public enum AdbDeviceStatus
-{
-	Online,
-	Offline,
-	Unauthorized,
-	NoPermissions,
-	NotRunning,
-	Unknown
-}
-
 /// <summary>
 /// Represents an Android device or emulator from 'adb devices -l' output.
 /// Mirrors the metadata produced by dotnet/android's GetAvailableAndroidDevices task.

src/Xamarin.Android.Tools.AndroidSdk/Models/AdbDeviceStatus.cs

@@ -0,0 +1,17 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace Xamarin.Android.Tools;
+
+/// <summary>
+/// Represents the status of an Android device.
+/// </summary>
+public enum AdbDeviceStatus
+{
+	Online,
+	Offline,
+	Unauthorized,
+	NoPermissions,
+	NotRunning,
+	Unknown
+}

src/Xamarin.Android.Tools.AndroidSdk/Models/AdbDeviceType.cs

@@ -0,0 +1,13 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace Xamarin.Android.Tools;
+
+/// <summary>
+/// Represents the type of an Android device.
+/// </summary>
+public enum AdbDeviceType
+{
+	Device,
+	Emulator
+}

src/Xamarin.Android.Tools.AndroidSdk/Runners/AdbRunner.cs

@@ -67,8 +67,11 @@ public async Task<IReadOnlyList<AdbDeviceInfo>> ListDevicesAsync (CancellationTo
 	{
 		var adb = RequireAdb ();
 		using var stdout = new StringWriter ();
+		using var stderr = new StringWriter ();
 		var psi = CreateAdbProcess (adb, "devices", "-l");
-		await ProcessUtils.StartProcess (psi, stdout, null, cancellationToken).ConfigureAwait (false);
+		var exitCode = await ProcessUtils.StartProcess (psi, stdout, stderr, cancellationToken).ConfigureAwait (false);
+
+		ProcessUtils.ThrowIfFailed (exitCode, "adb devices -l", stderr.ToString ());
 
 		var devices = ParseAdbDevicesOutput (stdout.ToString ());
 
@@ -103,8 +106,8 @@ public async Task<IReadOnlyList<AdbDeviceInfo>> ListDevicesAsync (CancellationTo
 			}
 		} catch (OperationCanceledException) {
 			throw;
-		} catch {
-			// Silently ignore failures (emulator may not support this command)
+		} catch (Exception) {
+			// Expected: emulator may not support 'emu avd name' command
 		}
 
 		return null;
@@ -125,7 +128,9 @@ public async Task WaitForDeviceAsync (string? serial = null, TimeSpan? timeout =
 		cts.CancelAfter (effectiveTimeout);
 
 		try {
-			await ProcessUtils.StartProcess (psi, null, null, cts.Token).ConfigureAwait (false);
+			using var stderr = new StringWriter ();
+			var exitCode = await ProcessUtils.StartProcess (psi, null, stderr, cts.Token).ConfigureAwait (false);
+			ProcessUtils.ThrowIfFailed (exitCode, "adb wait-for-device", stderr.ToString ());
 		} catch (OperationCanceledException) when (!cancellationToken.IsCancellationRequested) {
 			throw new TimeoutException ($"Timed out waiting for device after {effectiveTimeout.TotalSeconds}s.");
 		}
@@ -137,8 +142,11 @@ public async Task StopEmulatorAsync (string serial, CancellationToken cancellati
 			throw new ArgumentException ("Serial must not be empty.", nameof (serial));
 
 		var adb = RequireAdb ();
+		using var stderr = new StringWriter ();
 		var psi = CreateAdbProcess (adb, "-s", serial, "emu", "kill");
-		await ProcessUtils.StartProcess (psi, null, null, cancellationToken).ConfigureAwait (false);
+		var exitCode = await ProcessUtils.StartProcess (psi, null, stderr, cancellationToken).ConfigureAwait (false);
+
+		ProcessUtils.ThrowIfFailed (exitCode, $"adb -s {serial} emu kill", stderr.ToString ());
 	}
 
 	/// <summary>

src/Xamarin.Android.Tools.AndroidSdk/Runners/AvdManagerRunner.cs

@@ -172,7 +172,7 @@ internal static List<AvdInfo> ParseAvdListOutput (string output)
 	static string GetAvdRootDirectory ()
 	{
 		// ANDROID_AVD_HOME takes highest priority
-		var avdHome = Environment.GetEnvironmentVariable ("ANDROID_AVD_HOME");
+		var avdHome = Environment.GetEnvironmentVariable (EnvironmentVariableNames.AndroidAvdHome);
 		if (!string.IsNullOrEmpty (avdHome))
 			return avdHome;
 

src/Xamarin.Android.Tools.AndroidSdk/Runners/EmulatorRunner.cs

@@ -54,20 +54,24 @@ void ConfigureEnvironment (ProcessStartInfo psi)
 		AndroidEnvironmentHelper.ConfigureEnvironment (psi, getSdkPath (), getJdkPath?.Invoke ());
 	}
 
-	public Process StartAvd (string avdName, bool coldBoot = false, string? additionalArgs = null)
+	public Process StartAvd (string avdName, bool coldBoot = false, IEnumerable<string>? additionalArgs = null)
 	{
 		var emulatorPath = RequireEmulatorPath ();
 
 		var args = new List<string> { "-avd", avdName };
 		if (coldBoot)
 			args.Add ("-no-snapshot-load");
-		if (!string.IsNullOrEmpty (additionalArgs))
-			args.Add (additionalArgs);
+		if (additionalArgs != null)
+			args.AddRange (additionalArgs);
 
 		var psi = ProcessUtils.CreateProcessStartInfo (emulatorPath, args.ToArray ());
 		ConfigureEnvironment (psi);
 
 		var process = new Process { StartInfo = psi };
+		// Start directly instead of ProcessUtils.StartProcess because this is a
+		// long-running background process — we don't want to await its completion.
+		psi.RedirectStandardOutput = false;
+		psi.RedirectStandardError = false;
 		process.Start ();
 
 		return process;