CI: todoapp-uno / ios-maccatalyst build fails - .NET for iOS/MacCatalyst 26.5 requires Xcode 26.5, macos-latest only has Xcode 16.4 #559

Summary

Surfaced on PR #557 (run 29146179948, job todoapp-uno / ios-maccatalyst). The todoapp-uno / ios-maccatalyst job fails in the Build Uno project (iOS TFM only) step with the same Xcode-version-mismatch error previously diagnosed in #529 for todoapp-avalonia / ios and todoapp-maui / ios:

/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.Uno/TodoApp.Uno/TodoApp.Uno.csproj::TargetFramework=net10.0-ios]

Root cause

.github/workflows/build-samples-todoapp-uno.yml's ios-maccatalyst job still runs on floating macos-latest with no pinned Xcode version and no pinned iOS workload set:

  ios-maccatalyst:
    # iOS and Mac Catalyst builds both require Xcode, which is only available on macOS runners.
    runs-on: macos-latest
    steps:
      - name: Checkout Repository
        uses: actions/checkout@v7
      - name: Setup .NET
        uses: actions/setup-dotnet@v5
        with:
          dotnet-version: ${{ env.DOTNET_VERSION }}
      - name: Install iOS and Mac Catalyst workloads
        run: dotnet workload install ios maccatalyst
      - name: Restore Uno project (iOS TFM only)
        run: dotnet restore ${{ env.UnoProjectFile }} -p:TargetFramework=${{ env.iOSTargetFramework }}
      - name: Build Uno project (iOS TFM only)
        run: >
          dotnet build ${{ env.UnoProjectFile }}
          -f ${{ env.iOSTargetFramework }}
          --configuration ${{ env.DOTNET_CONFIGURATION }}
          --no-restore
      ...

dotnet workload install ios maccatalyst grabs whatever the latest Microsoft.iOS.Sdk.net10.0_* manifest advertises (currently 26.5, requiring Xcode 26.5), regardless of what Xcode version the macos-latest image actually ships (currently 16.4, per the same macos-15-arm64 image family diagnosed in #529).

This is the exact same class of failure as #529, which was fixed for todoapp-avalonia / ios and todoapp-maui / ios in #530 (merged 2026-07-10) by pinning the runner to macos-15, explicitly selecting an installed-but-non-default Xcode version via xcode-select, and pinning dotnet workload install ... --version <WorkloadSetVersion> to a workload set whose iOS/MacCatalyst SDK pack is compatible with that Xcode. .github/workflows/build-samples-todoapp-uno.yml existed before #530 (added in #511/#519, well before #530 merged) but wasn't included in that PR's scope, so the ios-maccatalyst job was missed and still floats on macos-latest with no pin.

Suggested fix

Apply the same pattern already used in build-samples-todoapp-avalonia.yml / build-samples-todoapp-maui.yml's ios jobs to the ios-maccatalyst job in build-samples-todoapp-uno.yml:

1. Pin runs-on: macos-15 instead of macos-latest.
2. Add a Select Xcode ${{ env.RequiredXcodeVersion }} step (sudo xcode-select -s /Applications/Xcode_${{ env.RequiredXcodeVersion }}.app) before Setup .NET, using the same RequiredXcodeVersion: '26.3' known to be installed (non-default) on the current macos-15 image.
3. Pin WorkloadSetVersion: '10.0.107' and pass --version ${{ env.WorkloadSetVersion }} to dotnet workload install ios maccatalyst, matching the resolved Microsoft.iOS.Sdk.net10.0_26.2.10233 / Xcode 26.3 pairing used by the Avalonia/MAUI jobs.
4. Keep both the iOS and Mac Catalyst restore/build steps in the single job as they are today, since both TFMs need the same pinned Xcode/workload set.

The exact pin values (macos-15, 26.3, 10.0.107) should be re-verified against whatever the current runner image/workload set state is at the time of the fix, in case they've drifted since #530.

To reproduce

Run the ios-maccatalyst job of .github/workflows/build-samples-todoapp-uno.yml on macos-latest as of the current runner image (Xcode 16.4 default). dotnet workload install ios maccatalyst 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/29146179948
• Failing job: https://github.com/CommunityToolkit/Datasync/actions/runs/29146179948/job/86528005085
• PR that surfaced it (unrelated change): docs: resolve CS1574 unresolved crefs and CS1571 duplicate param in TodoApp.BlazorWasm.Client TodoService #557
• Root-cause issue for the same failure class: CI: todoapp-avalonia / ios build fails - .NET for iOS 26.5 requires Xcode 26.5, macos-latest only has Xcode 16.4 #529
• Fix applied to Avalonia/MAUI: ci: pin iOS workload set + Xcode version for todoapp-avalonia/maui iOS builds #530
• CI workflow originally 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 (predates ci: pin iOS workload set + Xcode version for todoapp-avalonia/maui iOS builds #530)