Failure signature

The xamarin-macios-pr-apidiff Detect API changes job intermittently fails while compiling the generated file msbuild/Xamarin.MacDev.Tasks/Errors.designer.cs, despite unrelated PR scopes. The compiler reports impossible parse/read errors, and the downstream upload job then fails because change-detection.zip was never produced.

Confirmed occurrences

First observed: 2026-07-21 19:52 UTC. Latest observed: 2026-07-22 16:30 UTC. Recurrence: 2 jobs across 2 distinct monitored PRs.

Classification and impact

This is CI infrastructure/tooling behavior rather than a source regression:

• The affected PRs modify unrelated areas.
• Both failures target the same generated file in the same API-diff build phase but produce different corruption/read symptoms.
• The [tools] PreserveSmartEnumConversionsStep: emit root-descriptor XML instead of modifying (hot) reloadable assemblies. Fixes #26073 #26087 same-head automatic replacement succeeded without a source change addressing the file.
• The missing change-detection.zip error is downstream cascade, not a separate root cause.

The API-diff check blocks otherwise unrelated PRs.

Investigation

• Inspected Azure timelines and the failing build task logs.
• Confirmed [docs] Improve XML docs for PreserveAttribute, CLEnums, MKLocalSearch, and 12 more types #26241 failed in CoreCompile for Xamarin.MacDev.Tasks.csproj::TargetFramework=netstandard2.0.
• Correlated retained monitoring evidence from [tools] PreserveSmartEnumConversionsStep: emit root-descriptor XML instead of modifying (hot) reloadable assemblies. Fixes #26073 #26087.
• Searched all open and closed dotnet/macios issues using the file name, CS1504, CS1513, the out-of-range length message, and API-diff terminology; no matching issue was found.

Workaround

After confirming the PR is conflict-free, retry accounting is reconciled, and no equivalent build is active, rerun the failed API-diff stage/jobs. Azure task logs and generated artifacts have limited retention.