[CI Failure] Flaky: CanNewAndBuild(aspire-mstest, Net8) fails with Roslyn Method not found TryGetMaxCharCount on macOS

[github-actions]

Build Information

Build: https://github.com/microsoft/aspire/actions/runs/30654518872
Build error leg or test failing: Tests / Templates-MSTest_NewUpAndBuildSupportProjectTemplatesTests / Templates-MSTest_NewUpAndBuildSupportProjectTemplatesTests (macos-latest) / Aspire.Templates.Tests.MSTest_NewUpAndBuildSupportProjectTemplatesTests.CanNewAndBuild(templateName: "aspire-mstest", extraTestCreationArgs: "", sdk: Net8, tfm: Net8, error: null)
Pull request: #18947

Error Message

CSC : error CS1504: Source file '...GlobalUsings.g.cs' could not be opened -- Method not found: 'Boolean Microsoft.CodeAnalysis.EncodingExtensions.TryGetMaxCharCount(System.Text.Encoding, Int64, Int32 ByRef)'. Build FAILED.
at Aspire.Templates.Tests.CommandResult.EnsureExitCode
at Aspire.Templates.Tests.AspireProject.BuildAsync
at Aspire.Templates.Tests.NewUpAndBuildSupportProjectTemplatesBase.CanNewAndBuildActual

Description

Flaky: CanNewAndBuild(aspire-mstest, Net8) fails with Roslyn Method not found TryGetMaxCharCount on macOS

Type: flaky-test

Occurrences

Date	Build	Job	PR
2026-07-31	30654518872	Tests / Templates-MSTest_NewUpAndBuildSupportProjectTemplatesTests / Templates-MSTest_NewUpAndBuildSupportProjectTemplatesTests (macos-latest)	#18947
2026-09-18	35322237059	Tests / Package tests - macOS (class, Aspire.Templates.Tests, Templates-NUnit_NewUpAndBuildSupportProjectTemplatesTests... / Templates-NUnit_NewUpAndBuildSupportProjectTemplatesTests (macos-latest)	#19887

[radical]

[automated] The CI shepherd is watching this failure.

Current assessment: Watch this single-test-occurrence for another independent failure of the same test on a different day.

Evidence reviewed:

• issue:18950
• run:30654518872
• pr:18947

Evidence still needed:

• verified-fix-or-current-recurrence-check

Reassess when: After another independent failure of the same test on a different day or positive recovery.

No quarantine, retry, closure, or investigation has been started.