# ambiguous ReFS writable namespace paths are refused - #421
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Case-insensitive writable lookups selected the first matching row even when a directory contained names distinguished only by case. This could direct replacement, deletion or block clone at an unintended file. Require unique resolution both in the namespace walker and at the mutation entry points, and verify ambiguous synthetic images remain unchanged. The evidence is the existing ReFS row model and synthetic case-collision fixture; no external on-disk grammar is inferred.
Symptom: the offline-mutation test asserted only NotSupportedException, which Add also throws for a path it will not create, so the test passed even with the ambiguity check removed. Fix: assert the ambiguity message for every refused mutation, cover an ambiguous clone destination as well as an ambiguous source, and add the equivalence class of a unique case-folded path that must still resolve.
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git diff --checkpassed.This is an offline mutation safety fix. It does not enable native mounted ReFS writes or claim support for case-sensitive write semantics.
Review update
main.NotSupportedException.Addalso throws that for a path it will not create, so the test passed even with the ambiguity check removed. It now asserts the ambiguity message. It also covers an ambiguous clone destination, and a unique case-folded path that must still resolve.Compression.Tests.Refs59 passed, 1 skipped.RefsOfflineModifier.cstoo, but in a different region. Either merge order works. The second PR to merge should be rebased and its CI rerun.