Fix nullable Func delegate, whitespace, and csproj comment in PostTrimmingPipeline

[Copilot]

• Review copilot reviewer comment about repeated resolution attempts
• Memoize corlib assembly resolution in PostTrimmingPipeline.cs using a corlibResolutionAttempted flag and corlibAssembly local so resolution and error logging happen at most once per task execution

---

📍 Connect Copilot coding agent with Jira, Azure Boards or Linear to delegate work to Copilot in one click without leaving your project management tool.

[Copilot]

Pull request overview

Updates the post-trimming pipeline implementation in Xamarin.Android.Build.Tasks to align nullable delegate signatures, improve robustness when resolving System.Private.CoreLib, and keep the project file’s linker-source documentation accurate.

Changes:

• Add AssemblyResolutionException handling around resolver.Resolve("System.Private.CoreLib") in PostTrimmingPipeline.
• Update corlib factory delegate types from Func<AssemblyDefinition> to Func<AssemblyDefinition?> in the post-trimming keep-alives path, plus minor whitespace cleanup.
• Refresh the .csproj comment describing which linker sources are included.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
src/Xamarin.Android.Build.Tasks/Tasks/PostTrimmingPipeline.cs	Adds try/catch + error logging for corlib resolution used by post-trimming keep-alives.
src/Xamarin.Android.Build.Tasks/Linker/MonoDroid.Tuner/PostTrimmingAddKeepAlivesStep.cs	Updates the corlib factory delegate type to nullable to match new behavior.
src/Xamarin.Android.Build.Tasks/Linker/MonoDroid.Tuner/AddKeepAlivesHelper.cs	Propagates nullable delegate return type through helper methods and fixes indentation.
src/Xamarin.Android.Build.Tasks/Xamarin.Android.Build.Tasks.csproj	Updates comment documenting linker source inclusions for build tasks.

[sbomer]

@copilot apply changes based on the comments in this thread

[Copilot]

@copilot apply changes based on the comments in this thread

Applied in commit e6b2e5b. The corlib resolution is now memoized using a corlibResolutionAttempted flag and a corlibAssembly local captured in the lambda closure — resolution and error logging happen at most once per task execution regardless of how many assemblies/methods need KeepAlive injection.