[AI discovered CI] Scoped CSS compatibility publish fails during rzc generation #56138

Build Information

• Current build: 20260904.25
• Branch: refs/heads/main
• Failing test: Microsoft.NET.Sdk.StaticWebAssets.Tests.ScopedCssCompatibilityIntegrationTest.ScopedCss_PublishIsBackwardsCompatible_WithPreviousVersions
• Phase: test-execution
• Failure type: timeout
• Evidence sources: helix-trx
• Matching prior builds: 20260904.4, 20260903.17
• Failure fingerprint: test-execution|timeout|microsoft.net.sdk.staticwebassets.tests.scopedcsscompatibilityintegrationtest.scopedcss_publishisbackwardscompatible_withpreviousversions|test-method-microsoft.net.sdk.staticwebassets.tests.scopedcsscompatibilityintegrationtest.scopedcss_publishisbackwardscompatible_withpreviousversions-threw-exception-fluentassertio

Failure History

The same test and failure mechanism occurred in 3 supplied builds: the current build failed, build 1582866 failed, and build 1580853 failed. The surrounding recent sequence includes failures in builds 1582866 and 1580853, with successful builds 1583020 and 1582168 between/around them. This establishes recurrence; it does not by itself establish the product root cause.

Error Details

The test result reported:

Expected value to be 0 because Expected command to pass but it did not. Exit Code: 1

The command output included:

rzc generate exited with code 1.

The collector identified NETSDK1057: You are using a preview version of .NET in the generated project. Console, dump, and separate result links were not supplied in the evidence.

Root Cause Analysis

Observed: The backwards-compatibility publish test fails while invoking rzc generate; the command exits with code 1. The failure is recurring on the Windows x64 windows.amd64.vs2026.pre.scout.open queue, and the captured project emits NETSDK1057.

Assessment: The immediate cause is an unsuccessful Razor source-generation command during the compatibility publish flow. The evidence is consistent with the generated project using a preview SDK/package combination that is rejected or otherwise fails during rzc generate, but it does not establish whether the preview warning is causal or whether another generator/build error was omitted.

Confidence: High for the failing command and exit code; medium that preview SDK/package compatibility is involved; low for the deeper product cause.

Alternatives / Unknowns: The complete rzc console output, generated project assets, package graph, and binlog are not included, so a generator regression, incompatible previous-version package, or queue-specific SDK layout issue remains possible.

Suggested Investigation

First retrieve the full Helix console/result for work item Microsoft.NET.Sdk.StaticWebAssets.Tests.dll.11 and inspect the complete rzc generate diagnostics, rather than relying on the truncated NETSDK1057 line. Then compare the failing and last passing commits/builds, collect a binlog for the compatibility publish, and verify the SDK and package versions used by AppWithPackageAndP2PReference.

Error Message

{"ErrorMessage":["Microsoft.NET.Sdk.StaticWebAssets.Tests.ScopedCssCompatibilityIntegrationTest.ScopedCss_PublishIsBackwardsCompatible_WithPreviousVersions","FluentAssertions.Execution.AssertionFailedException","C:\h\w\BBE709EB\p\d\sdk\11.0.100-ci\Sdks\Microsoft.NET.Sdk\targets\Microsoft.NET.RuntimeIdentifierInference.targets(385,5): message NETSDK1057: You are using a preview version of .NET. See: (aka.ms/redacted) [C:\h\w\BBE709EB\t\dotnetSdkTests\4tky1tfe.jpl\ScopedCss_Pub---50D10F67\AppWithPackageAndP2PReference\AppWithPackageAndP2PReference.csproj]"],"BuildRetry":false,"ExcludeConsoleLog":false}

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