Move hardcoded error string in CompressAssemblies to Properties.Resources with XA5303 error code

Documentation/docs-mobile/messages/index.md

@@ -246,6 +246,7 @@ Either change the value in the AndroidManifest.xml to match the $(SupportedOSPla
 + [XA5300](xa5300.md): The Android/Java SDK Directory could not be found.
 + [XA5301](xa5301.md): Failed to generate Java type for class: {managedType} due to MAX_PATH: {exception}
 + [XA5302](xa5302.md): Two processes may be building this project at once. Lock file exists at path: {path}
++ [XA5303](xa5303.md): Failed to parse 'DescriptorIndex' metadata value '{value}' for assembly '{assembly}'.
 
 ## XA6xxx: Internal tools
 

Documentation/docs-mobile/messages/xa5303.md

@@ -0,0 +1,23 @@
+---
+title: .NET for Android error XA5303
+description: XA5303 error code
+ms.date: 05/20/2026
+f1_keywords:
+  - "XA5303"
+---
+
+# .NET for Android error XA5303
+
+## Example messages
+
+```
+error XA5303: Failed to parse 'DescriptorIndex' metadata value 'abc' for assembly 'MyAssembly.dll'.
+```
+
+## Issue
+
+The `DescriptorIndex` metadata on an assembly item passed to the `CompressAssemblies` MSBuild task could not be parsed as an unsigned integer. This metadata is required for LZ4 assembly compression.
+
+## Solution
+
+This is typically an internal build system error. If you encounter this error, please file a [bug report](https://github.com/dotnet/android/issues/new).

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

@@ -924,6 +924,12 @@ To use a custom JDK path for a command line build, set the 'JavaSdkDirectory' MS
   <data name="XA5302" xml:space="preserve">
     <value>Two processes may be building this project at once. Lock file exists at path: {0}</value>
   </data>
+  <data name="XA5303" xml:space="preserve">
+    <value>Failed to parse 'DescriptorIndex' metadata value '{0}' for assembly '{1}'.</value>
+    <comment>
+{0} - The DescriptorIndex metadata value that could not be parsed
+{1} - The assembly ItemSpec</comment>
+  </data>
   <data name="XA_Manifest_AutoGenerated_Header" xml:space="preserve">
     <value>
     This code was generated by a tool.

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

@@ -35,7 +35,7 @@ public override bool RunTask ()
 				break;
 
 			if (!uint.TryParse (descriptor_index_string, out var descriptor_index)) {
-				Log.LogError ($"Failed to parse 'DescriptorIndex' metadata value '{descriptor_index_string}' for assembly '{assembly.ItemSpec}'");
+				Log.LogCodedError ("XA5303", Properties.Resources.XA5303, descriptor_index_string, assembly.ItemSpec);
 				break;
 			}