keysDifferingOnlyInCaseAddressDistinctEntries

Two keys differing only in case.

StoreKey("a") and StoreKey("A") are distinct keys, and every legacy mapping in the tree passed both letters straight through — so on a case-insensitive filesystem they shared one file. APFS is case-insensitive by default, as are exFAT and NTFS; ext4 is not, which is exactly why nobody measured this: the defect is invisible on the filesystem most CI runs on.

After the fix it holds on every filesystem, because an uppercase letter is escaped and never reaches a filename at all.

What a green here proves depends on where it ran, and the difference is not small. There are two ways to fail this property and they are pinned unequally:

• a store that folds case itself — a lowercase() on the way to a filename — reds this on every target and every filesystem. That half is unconditional;

• a store that hands both keys to a case-folding filesystem reds only where the filesystem folds. Undoing the encoder's uppercase escaping is exactly that mutation, and it moves nothing at all in this suite on a case-sensitive runner.

theLegacyOverlapACaseFoldingFilesystemExposesIsExactlyTheDocumentedOne is where the second half is pinned unconditionally, by a route that does not depend on the filesystem.