Tracking flaky MountVolume tests that are hitting blocking-clean-ci:

• System.IO.Tests.Directory_Delete_MountVolume.RunTest failure #125295 — Directory_Delete_MountVolume.RunTest (16 hits/month)
• Directory_ReparsePoints_MountVolume test failures #125624 — Directory_ReparsePoints_MountVolume.runTest (4 hits/month)
• System.IO.Tests.Directory_Delete_MountVolume.RunTest occasionally fails in CI #125780 — closed as dupe of System.IO.Tests.Directory_Delete_MountVolume.RunTest failure #125295

Root cause (Delete_MountVolume): 7 locations use a fixed Task.Delay(300) after Directory.Delete through NTFS mount points, then assert !Directory.Exists(). 300ms is insufficient on loaded CI machines.

Root cause (ReparsePoints_MountVolume): Needs investigation — no Task.Delay in the test; may be mount setup/teardown timing.

Proposed fix: Replace fixed delays with a polling loop (retry Directory.Exists with backoff, ~10s timeout).

Known Issue Error Message

Fill the error message using step by step known issues guidance.

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