[CI] Intermittent actool exit code 255 failure on net11.0 iOS builds

[PureWeen]

Description

iOS device test and main builds on net11.0 are intermittently failing with actool exited with code 255 during asset catalog compilation. The failure produces an empty/unparseable asset-manifest.plist.

Error

.dotnet/packs/Microsoft.iOS.Sdk.net11.0_26.2/26.2.11547-net11-p3/tools/msbuild/Xamarin.Shared.targets(1021,3): error : actool exited with code 255

.dotnet/packs/Microsoft.iOS.Sdk.net11.0_26.2/26.2.11547-net11-p3/tools/msbuild/Xamarin.Shared.targets(1021,3): error : Failed to load actool log file `.../actool/asset-manifest.plist`: Failed to parse PList data type: 

Affected builds

• net11.0 branch (pre-existing):

  • Build #1361598 — maui-pr-devicetests, "Build DeviceTests" step (Apr 1)

• PR [automated] Merge branch 'main' => 'net11.0' #34789 (main → net11.0):

  • Build #1364489 — maui-pr-devicetests, "Build DeviceTests" step (Apr 2, passed on retrigger)

• PR [automated] Merge branch 'net11.0' => 'release/11.0.1xx-preview3' #34796 (net11.0 → release/11.0.1xx-preview3):

  • Build #1365430 — maui-pr, "Build macOS (Release)" step (Apr 3)
  • Build #1365432 — maui-pr-devicetests (Apr 3)

Observations

• Failure is intermittent — retriggers often pass (e.g., build #1364489 passed on retry)
• Occurs with Microsoft.iOS.Sdk.net11.0_26.2 versions 26.2.11547-net11-p3 and 26.2.11587-net11-p3
• Only affects net11.0-ios TFM builds, not net11.0-maccatalyst
• The actool tool exits with code 255 and produces an empty/invalid plist, suggesting it crashes or times out
• Checked last 5 net11.0 device test CI runs: 2 out of 5 had this failure

Impact

Blocks CI for net11.0 and downstream merge PRs. Currently requires manual retrigger to get past it.

[davidnguyen-tech]

Found a workaround locally for net11 P3:

DEVELOPER_DIR=/Applications/Xcode-26.3.0.app/Contents/Developer 
dotnet build -f net11.0-ios -c Debug -p:RuntimeIdentifier=ios-arm64

I have a multi-Xcode setup and my Xcode.app is a symlink to the version I need to use at the given moment.
Apparently that can cause issues.

[PureWeen]

@rolfbjarne @dalexsoto ?

[rolfbjarne]

This might have been fixed with #34978.

[davidnguyen-tech]

If #34978 focuses on simulators, does it implicitly fix the issue on physical devices as well?

[rolfbjarne]

If #34978 focuses on simulators, does it implicitly fix the issue on physical devices as well?

Yes, actool depends on having the correct simulator installed, even for device builds.

[dotMorten]

@rolfbjarne Just spent a bunch of time figuring out why my build got stuck on _CoreCompileImageAssets. I finally found this issue, and discovered my simulators were in a bad state.
Idea: Could you fail the build immediately with a helpful error instead, so people can quicker realize the issue and get unblocked?