[FastDeploy2] Copy staged files into private storage

[simonrozsival]

Summary

Alternative to #12310:

• push changed FastDeploy2 files to transient /data/local/tmp/fastdeploy2/<package>/<user> staging
• copy them into the app-private override directory with run-as cp -p
• remove staging after every deployment attempt, including failures
• store regular private files instead of persistent symlinks, so uninstall removes the deployed files with the application's data
• remove the symlink/copy mode and orphan-staging cleanup machinery
• invalidate the previous configuration-cache shape so existing symlink-based installations are recreated safely

Existing destination files are removed before copying so cp cannot follow symlinks left by an older FastDeploy2 deployment.

Performance

Head-to-head measurements on emulator-5554 (arm64-v8a), alternating implementation order:

Scenario	Runs	Previous symlink	Private copy	Difference
Assembly-only incremental install	12 each	3.821 s	4.074 s	+0.253 s (+6.6%)
Forced full FastDeploy redeploy	6 each	7.098 s	7.390 s	+0.292 s (+4.1%)

The corresponding median FastDeploy2 task times increased by 220 ms for an assembly-only update and 356 ms for a full redeploy. This is the cost of the additional private copy and staging cleanup commands.

Validation

• dotnet build src/Xamarin.Android.Build.Debugging.Tasks/Xamarin.Android.Build.Debugging.Tasks.csproj
• dotnet test bin/TestDebug/net10.0/Xamarin.Android.Build.Tests.dll --filter 'Name~FastDeploy2' — 2 passed
• FastDeploy2RemovesRemoteStagingDirectory device test — passed
• FastDeploymentStrategyCanBeChanged device test — passed
• verified deployed override assemblies are regular files and transient staging is absent after initial and incremental installs
• git diff --check

[Copilot]

Pull request overview

This PR changes the FastDeploy2 implementation to stage updated files under /data/local/tmp/fastdeploy2/<package>/<user> and then copy them into the app-private override directory using run-as cp -p, removing the previous symlink/copy mode split. It also ensures staging is removed after every deployment attempt and invalidates the prior configuration-cache shape so existing symlink-based installs are safely recreated as regular private files.

Changes:

• Switch FastDeploy2 from symlink-based override updates to copying regular files into app-private storage and always cleaning up transient staging.
• Remove the _AndroidFastDeployAppFileTransferMode property surface area (targets, task parameter, tests, and docs) and update the configuration-cache key accordingly.
• Update device/integration tests and documentation to reflect the new “regular file” override behavior and transient staging lifecycle.

Show a summary per file

File	Description
tests/MSBuildDeviceIntegration/Tests/FastDevTest.cs	Update device integration assertions from symlink to regular files; validate transient staging directory is removed after installs.
src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/DebuggingTasksTests.cs	Adjust FastDeploy2 warm-state probe parsing tests to match removed remote-staging hash tagging.
src/Xamarin.Android.Build.Debugging.Tasks/Xamarin.Android.Common.Debugging.targets	Remove transfer-mode property/validation, update configuration-cache shape, and pass ResetOverrideDirectory into FastDeploy2.
src/Xamarin.Android.Build.Debugging.Tasks/Tasks/FastDeploy2.WarmState.cs	Remove remote-staging marker checks from the warm-state probe and associated parsed state.
src/Xamarin.Android.Build.Debugging.Tasks/Tasks/FastDeploy2.Manifest.cs	Rework deployment flow to always reset transient staging, copy into private override storage, and remove staging in a finally cleanup.
src/Xamarin.Android.Build.Debugging.Tasks/Tasks/FastDeploy2.cs	Remove transfer-mode plumbing and simplify override update logic to “delete then cp -p” for changed files plus manifest marker handling.
Documentation/release-notes/11795.md	Update release notes to reflect removal of the transfer-mode property and the new copy-to-private approach.
Documentation/guides/FastDeploy2.md	Update guide for transient staging + private copy flow and revise marker/configuration behavior and command compatibility notes.

Review details

• Files reviewed: 8/8 changed files
• Comments generated: 0
• Review effort level: Lite