[xabt] fix incremental builds when @(AndroidManifestOverlay) changes (#11007)

Fixes: #11006

* Track AndroidManifestOverlay changes in _ManifestMerger

Ensure AndroidManifestOverlay items participate in _ManifestMerger incremental checks and add regression coverage for overlay-only manifest updates.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Jonathan Peppers <jonathan.peppers@microsoft.com>

Author: 3 people

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

@@ -213,6 +213,56 @@ public void OverlayManifestTest ([Values] AndroidRuntime runtime)
 			}
 		}
 
+		[Test]
+		public void OverlayManifestIncrementalBuildTest ([Values] AndroidRuntime runtime)
+		{
+			const bool isRelease = true;
+			if (IgnoreUnsupportedConfiguration (runtime, release: isRelease)) {
+				return;
+			}
+			var proj = new XamarinAndroidApplicationProject () {
+				IsRelease = isRelease,
+				ManifestMerger = "manifestmerger.jar",
+			};
+			proj.SetRuntime (runtime);
+			proj.AndroidManifest = @"<?xml version=""1.0"" encoding=""utf-8""?>
+<manifest xmlns:android=""http://schemas.android.com/apk/res/android"" android:versionCode=""1"" android:versionName=""1.0"" package=""foo.foo"">
+	<application android:label=""foo"">
+	</application>
+</manifest>";
+			var overlay = new BuildItem ("AndroidManifestOverlay", "ManifestOverlay.xml") {
+				TextContent = () => @"<?xml version=""1.0"" encoding=""utf-8""?>
+<manifest xmlns:android=""http://schemas.android.com/apk/res/android"">
+	<uses-permission android:name=""android.permission.CAMERA"" />
+</manifest>
+"
+			};
+			proj.OtherBuildItems.Add (overlay);
+			using (var b = CreateApkBuilder (cleanupAfterSuccessfulBuild: false, cleanupOnDispose: false)) {
+				Assert.IsTrue (b.Build (proj), "First build should have succeeded.");
+				var text = b.Output.GetIntermediaryAsText ("android/AndroidManifest.xml");
+				StringAssert.Contains ("android.permission.CAMERA", text, "Merged manifest should contain the initial overlay permission.");
+				StringAssert.DoesNotContain ("android.permission.RECORD_AUDIO", text, "Merged manifest should not contain the updated overlay permission yet.");
+
+				Assert.IsTrue (b.Build (proj, doNotCleanupOnUpdate: true, saveProject: false), "Second build should have succeeded.");
+				b.Output.AssertTargetIsSkipped ("_ManifestMerger");
+
+				overlay.TextContent = () => @"<?xml version=""1.0"" encoding=""utf-8""?>
+<manifest xmlns:android=""http://schemas.android.com/apk/res/android"">
+	<uses-permission android:name=""android.permission.CAMERA"" />
+	<uses-permission android:name=""android.permission.RECORD_AUDIO"" />
+</manifest>
+";
+				proj.Touch ("ManifestOverlay.xml");
+
+				Assert.IsTrue (b.Build (proj, doNotCleanupOnUpdate: true, saveProject: false), "Third build should have succeeded.");
+				b.Output.AssertTargetIsNotSkipped ("_ManifestMerger");
+
+				text = b.Output.GetIntermediaryAsText ("android/AndroidManifest.xml");
+				StringAssert.Contains ("android.permission.RECORD_AUDIO", text, "Merged manifest should include permissions from the updated overlay.");
+			}
+		}
+
 		[Test]
 		public void RemovePermissionTest ([Values] AndroidRuntime runtime)
 		{

src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets

@@ -1495,7 +1495,7 @@ because xbuild doesn't support framework reference assemblies.
 
 <Target Name="_ManifestMerger"
     Condition=" '$(AndroidManifestMerger)' == 'manifestmerger.jar' "
-    Inputs="$(IntermediateOutputPath)AndroidManifest.xml;@(ExtractedManifestDocuments);$(_AndroidBuildPropertiesCache);@(_AndroidMSBuildAllProjects)"
+    Inputs="$(IntermediateOutputPath)AndroidManifest.xml;@(ExtractedManifestDocuments);@(AndroidManifestOverlay);$(_AndroidBuildPropertiesCache);@(_AndroidMSBuildAllProjects)"
     Outputs="$(IntermediateOutputPath)android\AndroidManifest.xml"
   >
   <ItemGroup>