[dotnet run] ComputeAvailableDevices lists available emulators and auto-boot on deploy

.github/copilot-instructions.md

@@ -129,10 +129,12 @@ if (!UncompressedFileExtensions.IsNullOrWhiteSpace ()) {
 ## Formatting
 
 C# code uses tabs (not spaces) and Mono style (`.editorconfig`):
+- **NEVER** use `!` (null-forgiving operator) in C# code. Always refactor to avoid it, e.g. by having helper methods return non-null types or by checking for null explicitly.
 - Preserve existing formatting and comments
 - Space before `(` and `[`: `Foo ()`, `array [0]`
 - Use `""` not `string.Empty`, `[]` not `Array.Empty<T>()`
 - Minimal diffs - don't leave random empty lines
+- Do NOT use `#region` or `#endregion`
 
 ```csharp
 Foo ();

src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.Application.targets

@@ -10,6 +10,7 @@ This file contains targets specific for Android application projects.
   <UsingTask TaskName="Xamarin.Android.Tasks.AndroidAdb" AssemblyFile="$(_XamarinAndroidBuildTasksAssembly)" />
   <UsingTask TaskName="Xamarin.Android.Tasks.GetAndroidActivityName" AssemblyFile="$(_XamarinAndroidBuildTasksAssembly)" />
   <UsingTask TaskName="Xamarin.Android.Tasks.GetAvailableAndroidDevices" AssemblyFile="$(_XamarinAndroidBuildTasksAssembly)" />
+  <UsingTask TaskName="Xamarin.Android.Tasks.BootAndroidEmulator" AssemblyFile="$(_XamarinAndroidBuildTasksAssembly)" />
   <UsingTask TaskName="Xamarin.Android.BuildTools.PrepTasks.XASleepInternal" AssemblyFile="$(_XamarinAndroidBuildTasksAssembly)" />
 
   <PropertyGroup>
@@ -44,11 +45,47 @@ This file contains targets specific for Android application projects.
       Returns="@(Devices)">
     <GetAvailableAndroidDevices
         ToolExe="$(AdbToolExe)"
-        ToolPath="$(AdbToolPath)">
+        ToolPath="$(AdbToolPath)"
+        EmulatorToolExe="$(EmulatorToolExe)"
+        EmulatorToolPath="$(EmulatorToolPath)">
       <Output TaskParameter="Devices" ItemName="Devices" />
     </GetAvailableAndroidDevices>
   </Target>
 
+  <!--
+  ***********************************************************************************************
+  _EnsureDeviceBooted
+
+  Target that ensures the selected device is online and ready. If $(Device) refers to an
+  unbooted AVD, this target boots the emulator and updates $(AdbTarget) to the resolved
+  ADB serial (e.g. "-s emulator-5554").
+  Runs before _GetPrimaryCpuAbi (in commercial builds) so $(AdbTarget) is correct,
+  and before _DeployApk/_DeployAppBundle (which use AdbTarget for adb commands)
+  when $(Device) is set.
+
+  Note: this target CANNOT use DependsOnTargets="_ResolveMonoAndroidSdks" because in commercial
+  builds _GetPrimaryCpuAbi is in $(_ResolveMonoAndroidSdksDependsOn), which would create a cycle:
+    _ResolveMonoAndroidSdks -> _GetPrimaryCpuAbi -> _EnsureDeviceBooted -> _ResolveMonoAndroidSdks
+  Instead, the task computes tool paths from $(AndroidSdkDirectory), which is available because
+  _ResolveSdks runs earlier in the dependency chain.
+  ***********************************************************************************************
+  -->
+  <Target Name="_EnsureDeviceBooted"
+      BeforeTargets="_GetPrimaryCpuAbi;_DeployApk;_DeployAppBundle"
+      Condition=" '$(Device)' != '' ">
+    <BootAndroidEmulator
+        Device="$(Device)"
+        AndroidSdkDirectory="$(AndroidSdkDirectory)"
+        EmulatorToolExe="$(EmulatorToolExe)"
+        EmulatorToolPath="$(EmulatorToolPath)"
+        AdbToolExe="$(AdbToolExe)"
+        AdbToolPath="$(AdbToolPath)"
+        BootTimeoutSeconds="$(BootTimeoutSeconds)"
+        EmulatorExtraArguments="$(EmulatorExtraArguments)">
+      <Output TaskParameter="AdbTarget" PropertyName="AdbTarget" />
+    </BootAndroidEmulator>
+  </Target>
+
   <Target Name="_AndroidComputeRunArguments"
       BeforeTargets="ComputeRunArguments"
       DependsOnTargets="$(_AndroidComputeRunArgumentsDependsOn)">

src/Xamarin.Android.Build.Tasks/Properties/Resources.resx

@@ -1073,6 +1073,22 @@ To use a custom JDK path for a command line build, set the 'JavaSdkDirectory' MS
     <value>Command '{0}' failed.\n{1}</value>
     <comment>'{0}' is a failed command name (potentially with path) followed by all the arguments passed to it. {1} is the combined output on the standard error and standard output streams.</comment>
   </data>
+  <data name="XA0143" xml:space="preserve">
+    <value>Failed to launch the Android emulator for AVD '{0}': {1}</value>
+    <comment>{0} - The AVD name.
+{1} - The exception message.</comment>
+  </data>
+  <data name="XA0144" xml:space="preserve">
+    <value>The Android emulator for AVD '{0}' exited unexpectedly with exit code {1} before becoming available.</value>
+    <comment>{0} - The AVD name.
+{1} - The process exit code.</comment>
+  </data>
+  <data name="XA0145" xml:space="preserve">
+    <value>The Android emulator for AVD '{0}' did not finish booting within {1} seconds. Increase 'BootTimeoutSeconds' or check the emulator configuration.</value>
+    <comment>The following is a literal name and should not be translated: BootTimeoutSeconds
+{0} - The AVD name.
+{1} - The timeout in seconds.</comment>
+  </data>
   <data name="XAGRDL1000" xml:space="preserve">
     <value>Executable 'gradlew' not found in project directory '{0}'. Please ensure the path to your Gradle project folder is correct, and that it contains Gradle Wrapper scripts.</value>
     <comment>The following are literal names and should not be translated: gradlew, Gradle, Gradle Wrapper