[CI] LinkSdk SpecialFolder intermittently reports protected folders as writable

[dalexsoto]

Failure signature

LinkSdk.LinkSdkRegressionTest.SpecialFolder intermittently reports a protected special folder as writable:

Assert.That(readOnly, Is.True)
Expected: True
But was: False

Confirmed occurrences

PR / head	Build and job	Platform / folder	Outcome
#25979 / bf96da28d2420b4b949ae80f3b8a50caec3b032b	14720177 - linker_macos	macOS / Desktop	The bot reported the folder writable. Simulator-tests attempt 2 was accepted at 22:52 UTC and remains queued.
#26220 / 7176ce0bfb7c08ff0b983388ffda1fdf7195c0db	14721806 - linker_maccatalyst	Mac Catalyst / MyDocuments	The bot reported the folder writable. The build remains active.

First observed: 2026-07-21 20:02 UTC. Latest observed: 2026-07-22 00:08 UTC. Recurrence: 2 jobs across 2 distinct monitored PRs.

Classification and impact

This is a genuinely flaky environment/test failure, not a source regression. It occurs in unrelated PRs on different Apple platforms, while sibling linker variations pass. The stable signature is the same test and read-only assertion; only the special-folder value differs.

Investigation

• Inspected TestSummary and HtmlReport artifacts for both failures.
• Confirmed the exact readOnly assertion and unrelated PR change scopes.
• Searched open and closed dotnet/macios issues by test name, folder names, and assertion text.
• Closed issue [dotnet] LinkSdk.LinkSdkRegressionTest.SpecialFolder fails on tvOS #12640 concerns a different tvOS folder-existence/test-order failure, not this read-only mismatch.

Workaround

Rerun failed jobs after confirming mergeability and retry budgets. Do not submit another retry while an equivalent stage attempt is queued or running. Azure artifacts have limited retention.

[dalexsoto]

Retry update for PR #26220: build 14721806 is terminal, and retained history shows zero prior retries. Simulator_tests attempt 2 was accepted at 02:50 UTC to rerun linker_maccatalyst together with the slow-Xcode monotouch_ios failure.

[dalexsoto]

Retry outcome: PR #25979 build 14720177 simulator_tests attempt 2 completed successfully. Linker_macos passed, and the overall build result is succeeded.

[dalexsoto]

New affected PR: #26140 @ ee2a104313d59c2bbc6646e2bd8caeb9dac30de5, build 14728986, job linker_macos. LinkSdkRegressionTest.SpecialFolder reported Desktop writable in a PrepareAssemblies/CoreCLR variation.

The signature now affects 3 jobs across 3 monitored PRs. No retry was submitted because build 14728986 remains active and same-head replacement build 14729205 is also active.

[dalexsoto]

Final retry outcome: merged PR #26220 build 14721806 simulator_tests attempt 2 completed successfully. Linker_maccatalyst passed, the overall build succeeded, and the PR merged at 06:52 UTC.

[dalexsoto]

Outcome for PR #26140 @ ee2a104313d59c2bbc6646e2bd8caeb9dac30de5: same-head replacement build 14729205 completed linker_macos successfully at 07:22 UTC, so the LinkSdkRegressionTest.SpecialFolder failure did not reproduce. The original build 14728986 was later canceled after the replacement was queued.