Update copilot-instructions.md with learnings from recent PRs

[rmarinho]

Summary

Updates .github/copilot-instructions.md with learnings from recent PRs (#10949, #10969, #10971 and dotnet/android-tools#312).

Changes

Architecture

• Document external/xamarin-android-tools/ submodule — it contains key shared infrastructure (AndroidTask/AsyncTask base classes, AdbRunner, EmulatorRunner, NRT extensions, CreateTaskLogger)

MSBuild Tasks

• Clarify that AsyncTask should be used for tasks needing async/await (not just AndroidTask)

Error Patterns (expanded section)

• Error messages must come from Properties.Resources — previously not documented, led to hardcoded strings in AI-generated code
• Error code lifecycle — when removing functionality, clean up or repurpose the XA#### code; don't leave orphaned entries in Resources.resx
• AsyncTask logging — use thread-safe LogCodedError()/LogMessage() helpers instead of Log.* which is [Obsolete] on AsyncTask and can hang Visual Studio

Nullable Reference Types

• ! workarounds for test code — document how to avoid null! in [SetUp] fields (use nullable types) and after Assert.IsNotNull (extract to local variable)

Context

These gaps caused real issues during PR development:

• Using Log.LogCodedError from AsyncTask async context (should use LogCodedError)
• Orphaned XA0144 error code after refactoring
• null! pattern in test fields flagged by all 4 AI models during multi-model code review
• Hardcoded error strings instead of Properties.Resources

[Copilot]

Pull request overview

Updates .github/copilot-instructions.md to capture recent learnings about task base classes, error patterns, and nullable reference type guidance, and bumps the external/xamarin-android-tools submodule to a newer commit.

Changes:

• Document external/xamarin-android-tools/ as shared SDK tooling and infrastructure.
• Clarify guidance for when to use AsyncTask (async/await) vs AndroidTask.
• Expand error-pattern guidance (resource-based messages, error code lifecycle, and AsyncTask logging best practices) and add NRT guidance for tests.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
external/xamarin-android-tools	Updates the submodule pointer to a newer upstream commit.
.github/copilot-instructions.md	Adds/clarifies guidance on repo architecture, MSBuild task patterns, error handling, and NRT usage in tests.

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[Copilot]

Pull request overview

Updates the repo’s AI contribution guidance (.github/copilot-instructions.md) based on recent MSBuild/emulator work, with emphasis on shared tooling, correct MSBuild task base classes, localized error patterns, and nullable-reference-type practices in tests.

Changes:

• Document external/xamarin-android-tools/ as shared infrastructure used by this repo’s build/task ecosystem.
• Clarify MSBuild task guidance to use AsyncTask when async/await is required.
• Expand error/nullable/test guidance (localized Properties.Resources messages, XA code lifecycle, avoiding ! in tests) and add a macOS emulator troubleshooting note.

[Copilot]

The guidance to remove an XA#### entry from Resources.Designer.cs is misleading: this file is auto-generated and manual edits will be lost. Suggest updating this bullet to say to remove/repurpose the entry in Resources.resx and then regenerate the designer (rebuild/resgen), rather than editing Resources.Designer.cs directly.

Suggested change

	-**Error code lifecycle:** When removing functionality that used an `XA####` code, either repurpose the code or remove it from `Resources.resx` and `Resources.Designer.cs`. Don't leave orphaned codes.
	-**Error code lifecycle:** When removing functionality that used an `XA####` code, either repurpose the code or remove/rename the corresponding entry in `Resources.resx` and then regenerate `Resources.Designer.cs` (e.g., by rebuilding or running `resgen`). `Resources.Designer.cs` is auto-generated and should not be edited manually. Don't leave orphaned codes.