CI: todoapp-avalonia / ios build fails - .NET for iOS 26.5 requires Xcode 26.5, macos-latest only has Xcode 16.4 #529

Summary

Surfaced on PR #528 (run 29064641347, job todoapp-avalonia / ios), which only replaces obsolete DisplayAlert with DisplayAlertAsync in TodoApp.Avalonia - it does not touch anything related to iOS or the workload setup. The todoapp-avalonia / ios job (added in #511 / #519) fails in the Build iOS project step:

/Users/runner/.dotnet/packs/Microsoft.iOS.Sdk.net10.0_26.5/26.5.10284/targets/Xamarin.Shared.Sdk.targets(2570,3):
error : This version of .NET for iOS (26.5.10284) requires Xcode 26.5. The current version of Xcode is 16.4.
Either install Xcode 26.5, or use a different version of .NET for iOS.
See https://aka.ms/xcode-requirement for more information.
[/Users/runner/work/Datasync/Datasync/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia.iOS/TodoApp.Avalonia.iOS.csproj]

Job details:

• Runner: macos-latest → resolved to image macos-15-arm64, version 20260706.0213.1, macOS 15.7.7
• Installed Xcode on that image: 16.4
• dotnet workload install ios step succeeds and installs Microsoft.iOS.Sdk.net10.0_26.5 version 26.5.10284, which requires Xcode 26.5
• Build then fails with the version-mismatch error above

Why this looks like an environment/workload issue, not a code issue

The PR diff for #528 only changes a DisplayAlert → DisplayAlertAsync call in TodoApp.Avalonia - nothing in TodoApp.Avalonia.iOS, workload setup, or CI config. The dotnet build output shows the shared TodoApp.Avalonia project (which contains the PR's change) restores and builds fine; the failure happens purely in the Xamarin.Shared.Sdk.targets Xcode-version check for the net10.0-ios head.

Interesting corroborating data point from the same run: the sibling todoapp-maui / ios job (also runs-on: macos-latest, same Xcode 16.4) succeeded. Its dotnet workload install maui-ios step installs multiple iOS SDK pack versions side-by-side:

Installing pack Microsoft.iOS.Sdk.net10.0_26.5 version 26.5.10284...
Installing pack Microsoft.iOS.Sdk.net9.0_18.0 version 18.0.9617...
Installing pack Microsoft.iOS.Sdk.net9.0_26.5 version 26.5.9002...
Installing pack Microsoft.iOS.Sdk.net10.0_26.0 version 26.0.11017...

...and its build actually resolves to Microsoft.iOS.Sdk.net10.0_26.0 (26.0.11017), which is compatible with the installed Xcode 16.4, rather than the newer 26.5 pack. The ios workload (used by TodoApp.Avalonia.iOS, a plain Microsoft.NET.Sdk project referencing Avalonia.iOS) apparently only registers/selects the newest net10.0_26.5 pack and has no fallback, so it hits the hard Xcode-version check instead of negotiating down to a pack compatible with the runner's installed Xcode.

Affected workflow

• .github/workflows/build-samples-todoapp-avalonia.yml, job ios:

  ios:
    runs-on: macos-latest
    steps:
      - uses: actions/checkout@v7
      - uses: actions/setup-dotnet@v5
        with:
          dotnet-version: ${{ env.DOTNET_VERSION }}   # 10.0.x
      - name: Install iOS workload
        run: dotnet workload install ios
      - name: Restore iOS project
        run: dotnet restore ${{ env.iOSProjectFile }}
      - name: Build iOS project
        run: dotnet build ${{ env.iOSProjectFile }} --configuration ${{ env.DOTNET_CONFIGURATION }} --no-restore

  No Xcode/workload version is pinned; dotnet workload install ios grabs whatever the latest Microsoft.iOS.Sdk.net10.0_* manifest advertises (currently 26.5, which requires Xcode 26.5), regardless of what Xcode version the macos-latest image actually ships (currently 16.4).

Suggested fixes (any of)

1. Pin a specific Microsoft.iOS.Sdk / rollback workload version for the ios workload install (e.g. dotnet workload install ios --version <manifest-version> or a rollback.json) so it matches whatever Xcode ships on macos-latest.
2. Pin the runner to a specific macOS image/Xcode version instead of floating macos-latest (e.g. macos-15 and/or xcode-select to a known-good Xcode, similar to how maccy/xcode-select@... or maxim-lobanov/setup-xcode@v1 could be used), and keep it in sync with the .NET for iOS SDK's requirement.
3. Investigate why the plain ios workload doesn't negotiate down to a compatible pack the way maui-ios does in the same run, and consider aligning TodoApp.Avalonia.iOS's workload install with whatever mechanism lets maui-ios pick net10.0_26.0 automatically.

To reproduce

Run the ios job of .github/workflows/build-samples-todoapp-avalonia.yml (or build-samples-todoapp-maui.yml for a comparison) on macos-latest as of image macos-15-arm64 20260706.0213.1 (Xcode 16.4). The plain ios workload install pulls Microsoft.iOS.Sdk.net10.0_26.5 (26.5.10284) and building net10.0-ios fails with the Xcode-version-mismatch error above.

References

• Failing run: https://github.com/CommunityToolkit/Datasync/actions/runs/29064641347
• Failing job: https://github.com/CommunityToolkit/Datasync/actions/runs/29064641347/job/86314313188
• PR that surfaced it (unrelated change): Replace obsolete DisplayAlert with DisplayAlertAsync #528
• CI added in: Add CI workflow to build mobile /samples heads: Android, iOS, Uno (Phase 3 of #509) #511 / ci: add build-samples workflow for Phase 3 mobile heads (#511) #519
• Microsoft doc referenced in the error: https://aka.ms/xcode-requirement
• Runner image migration notice also seen on this job (informational, likely unrelated): macos-latest will migrate to macOS 26 beginning June 15, 2026 - [macOS] macos-latest label will use macos-26 in June 2026 actions/runner-images#14167