[xabt] Fix dotnet run failing with multiple AVDs present (#11001)

Fixes: #10998

When multiple AVD emulator images are defined but only one device is
running, 'dotnet run' incorrectly considers all AVDs (including
non-running ones) as available targets, causing a device selection
prompt or error in non-interactive mode.

Add FilterDevicesForSelection() to GetAvailableAndroidDevices that
filters the merged device list: when any online devices exist, only
online devices are returned (enabling auto-selection when a single
device is running). When no online devices exist, all devices are
returned including non-running emulators so the user can pick one
to boot.

## Address review: avoid allocation when no filtering needed

Two-pass approach in FilterDevicesForSelection: first determine if
filtering is needed, then allocate only when mixed online/offline
states exist. Returns the original list when all devices share the
same status.

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

Author: rmarinho

src/Xamarin.Android.Build.Tasks/Tasks/GetAvailableAndroidDevices.cs

@@ -12,8 +12,10 @@ namespace Xamarin.Android.Tasks;
 
 /// <summary>
 /// MSBuild task that queries available Android devices and emulators using 'adb devices -l'
-/// and 'emulator -list-avds'. Merges the results to provide a complete list of available
-/// devices including emulators that are not currently running.
+/// and 'emulator -list-avds'. Merges the results and filters them for device selection:
+/// when any online devices exist, only online devices are returned (enabling auto-selection
+/// when a single device is running). When no online devices exist, all devices are returned
+/// including non-running emulators (allowing the user to pick one to boot).
 /// Returns a list of devices with metadata for device selection in dotnet run.
 ///
 /// Parsing and merging logic is delegated to <see cref="AdbRunner"/> in Xamarin.Android.Tools.AndroidSdk.
@@ -74,14 +76,40 @@ public override bool RunTask ()
         // Merge using shared logic
         var mergedDevices = AdbRunner.MergeDevicesAndEmulators (adbDevices, availableEmulators, logger);
 
+        // Filter: if any online devices exist, return only those so auto-selection works
+        // when a single device is running. If none are online, return all (including
+        // non-running emulators) so the user can pick one to boot.
+        var filteredDevices = FilterDevicesForSelection (mergedDevices);
+        Log.LogDebugMessage ($"Filtered from {mergedDevices.Count} to {filteredDevices.Count} device(s) (online devices take priority)");
+
         // Convert to ITaskItem array
-        Devices = ConvertToTaskItems (mergedDevices);
+        Devices = ConvertToTaskItems (filteredDevices);
 
-        Log.LogDebugMessage ($"Total {Devices.Length} Android device(s)/emulator(s) after merging");
+        Log.LogDebugMessage ($"Total {Devices.Length} Android device(s)/emulator(s) after filtering");
 
         return !Log.HasLoggedErrors;
     }
 
+    /// <summary>
+    /// Filters the merged device list for device selection:
+    /// - If any online devices exist, returns only those (so auto-selection works with a single running device)
+    /// - If no online devices exist, returns all (including non-running emulators for user selection)
+    /// </summary>
+    internal static IReadOnlyList<AdbDeviceInfo> FilterDevicesForSelection (IReadOnlyList<AdbDeviceInfo> devices)
+    {
+        var onlineDevices = new List<AdbDeviceInfo> (devices.Count);
+        foreach (var device in devices) {
+            if (device.Status == AdbDeviceStatus.Online) {
+                onlineDevices.Add (device);
+            }
+        }
+
+        if (onlineDevices.Count == 0)
+            return devices;
+
+        return onlineDevices;
+    }
+
     /// <summary>
     /// Converts AdbDeviceInfo list to ITaskItem array for MSBuild output.
     /// </summary>

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Tasks/GetAvailableAndroidDevicesTests.cs

@@ -706,6 +706,106 @@ public void MergeDevicesAndEmulators_NonRunningEmulatorHasFormattedDescription (
 			Assert.AreEqual ("Pixel 7 Pro API 35 (Not Running)", result [0].GetMetadata ("Description"), "Description should be formatted with (Not Running) suffix");
 		}
 
+		[Test]
+		public void FilterDevicesForSelection_SingleOnlineDevice_WithNonRunningEmulators_ReturnsOnlyOnline ()
+		{
+			var devices = new List<AdbDeviceInfo> {
+				CreateDeviceInfo ("emulator-5554", "Pixel 8 API 36 X64", AdbDeviceType.Emulator, AdbDeviceStatus.Online),
+				CreateDeviceInfo ("pixel_3_xl_api_22_arm", "Pixel 3 XL API 22 Arm (Not Running)", AdbDeviceType.Emulator, AdbDeviceStatus.NotRunning),
+				CreateDeviceInfo ("pixel_3_xl_api_22_x86", "Pixel 3 XL API 22 X86 (Not Running)", AdbDeviceType.Emulator, AdbDeviceStatus.NotRunning),
+				CreateDeviceInfo ("pixel_4_api_30_amd64", "Pixel 4 API 30 Amd64 (Not Running)", AdbDeviceType.Emulator, AdbDeviceStatus.NotRunning),
+			};
+
+			var filtered = GetAvailableAndroidDevices.FilterDevicesForSelection (devices);
+
+			Assert.AreEqual (1, filtered.Count, "Should return only the single running device");
+			Assert.AreEqual ("emulator-5554", filtered [0].Serial);
+			Assert.AreEqual (AdbDeviceStatus.Online, filtered [0].Status);
+		}
+
+		[Test]
+		public void FilterDevicesForSelection_SinglePhysicalDevice_WithNonRunningEmulators_ReturnsOnlyOnline ()
+		{
+			var devices = new List<AdbDeviceInfo> {
+				CreateDeviceInfo ("0A041FDD400327", "Pixel 5", AdbDeviceType.Device, AdbDeviceStatus.Online),
+				CreateDeviceInfo ("pixel_7_api_35", "Pixel 7 API 35 (Not Running)", AdbDeviceType.Emulator, AdbDeviceStatus.NotRunning),
+				CreateDeviceInfo ("pixel_9_api_36", "Pixel 9 API 36 (Not Running)", AdbDeviceType.Emulator, AdbDeviceStatus.NotRunning),
+			};
+
+			var filtered = GetAvailableAndroidDevices.FilterDevicesForSelection (devices);
+
+			Assert.AreEqual (1, filtered.Count, "Should return only the single running physical device");
+			Assert.AreEqual ("0A041FDD400327", filtered [0].Serial);
+		}
+
+		[Test]
+		public void FilterDevicesForSelection_MultipleOnlineDevices_ReturnsOnlyOnline ()
+		{
+			var devices = new List<AdbDeviceInfo> {
+				CreateDeviceInfo ("0A041FDD400327", "Pixel 5", AdbDeviceType.Device, AdbDeviceStatus.Online),
+				CreateDeviceInfo ("emulator-5554", "Pixel 8 API 36", AdbDeviceType.Emulator, AdbDeviceStatus.Online),
+				CreateDeviceInfo ("pixel_7_api_35", "Pixel 7 API 35 (Not Running)", AdbDeviceType.Emulator, AdbDeviceStatus.NotRunning),
+			};
+
+			var filtered = GetAvailableAndroidDevices.FilterDevicesForSelection (devices);
+
+			Assert.AreEqual (2, filtered.Count, "Should return only the 2 online devices");
+			Assert.IsTrue (filtered.All (d => d.Status == AdbDeviceStatus.Online), "All returned devices should be online");
+		}
+
+		[Test]
+		public void FilterDevicesForSelection_NoOnlineDevices_ReturnsAll ()
+		{
+			var devices = new List<AdbDeviceInfo> {
+				CreateDeviceInfo ("pixel_7_api_35", "Pixel 7 API 35 (Not Running)", AdbDeviceType.Emulator, AdbDeviceStatus.NotRunning),
+				CreateDeviceInfo ("pixel_9_api_36", "Pixel 9 API 36 (Not Running)", AdbDeviceType.Emulator, AdbDeviceStatus.NotRunning),
+			};
+
+			var filtered = GetAvailableAndroidDevices.FilterDevicesForSelection (devices);
+
+			Assert.AreEqual (2, filtered.Count, "Should return all devices when none are online");
+		}
+
+		[Test]
+		public void FilterDevicesForSelection_EmptyList_ReturnsEmpty ()
+		{
+			var devices = new List<AdbDeviceInfo> ();
+
+			var filtered = GetAvailableAndroidDevices.FilterDevicesForSelection (devices);
+
+			Assert.AreEqual (0, filtered.Count, "Should return empty list");
+		}
+
+		[Test]
+		public void FilterDevicesForSelection_OnlineDeviceWithOfflineDevice_ReturnsOnlyOnline ()
+		{
+			var devices = new List<AdbDeviceInfo> {
+				CreateDeviceInfo ("0A041FDD400327", "Pixel 5", AdbDeviceType.Device, AdbDeviceStatus.Online),
+				CreateDeviceInfo ("DEADBEEF123456", "Pixel 3", AdbDeviceType.Device, AdbDeviceStatus.Offline),
+				CreateDeviceInfo ("pixel_7_api_35", "Pixel 7 API 35 (Not Running)", AdbDeviceType.Emulator, AdbDeviceStatus.NotRunning),
+			};
+
+			var filtered = GetAvailableAndroidDevices.FilterDevicesForSelection (devices);
+
+			Assert.AreEqual (1, filtered.Count, "Should return only the online device, filtering offline and non-running");
+			Assert.AreEqual ("0A041FDD400327", filtered [0].Serial);
+		}
+
+		[Test]
+		public void FilterDevicesForSelection_OnlineDeviceWithUnauthorizedDevice_ReturnsOnlyOnline ()
+		{
+			var devices = new List<AdbDeviceInfo> {
+				CreateDeviceInfo ("0A041FDD400327", "Pixel 5", AdbDeviceType.Device, AdbDeviceStatus.Online),
+				CreateDeviceInfo ("UNAUTHORIZED001", "Unknown", AdbDeviceType.Device, AdbDeviceStatus.Unauthorized),
+				CreateDeviceInfo ("pixel_7_api_35", "Pixel 7 API 35 (Not Running)", AdbDeviceType.Emulator, AdbDeviceStatus.NotRunning),
+			};
+
+			var filtered = GetAvailableAndroidDevices.FilterDevicesForSelection (devices);
+
+			Assert.AreEqual (1, filtered.Count, "Should return only the online device, filtering unauthorized and non-running");
+			Assert.AreEqual ("0A041FDD400327", filtered [0].Serial);
+		}
+
 		/// <summary>
 		/// Helper method to create an AdbDeviceInfo for testing
 		/// </summary>