The core gains Swift's virtual file system (paths, case-insensitive
lookup that keeps the spelling, quotas, atomic changes, the defaults of
a new device) and the string behaviour the ported code relies on without
saying so. Both are measured in the Swift oracle: 11 file system cases
(the three Swift tests among them) step by step, and trimming, lower
case, equality, ordering and Base64 case by case — whitespace and control
characters over all of Unicode.
Found by measuring:
- Swift trims NEL and ZERO WIDTH SPACE, not the BOM; JS trim() does the
opposite. The .fls import now trims with swiftTrim.
- lowercased() maps scalar by scalar: a word-final sigma stays σ.
- Foundation decodes "====" and "Y===" as empty data.
- Foundation on Linux counts 24,735 plane-14 scalars as control
characters, a table artefact; the port keeps Unicode Cc+Cf.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
