diff --git a/CHANGES.md b/CHANGES.md
index a9ccd00..a58004e 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -28,10 +28,11 @@ Swift-Pfade relativ zu `filius-ipad/ios/FiliusPad/TopologyEditor/` (Stand
 
 | Datei | Quelle | Art der Übertragung |
 | --- | --- | --- |
-| `src/zip.ts` | `Persistence/TopologyFLSArchive.swift` (Fehler, Grenzen, Pfadregeln, ZIP-Leser/-Schreiber, CRC-32) | übertragen; DEFLATE über `fflate`, mit Apples Abschneide-Verhalten nachgebildet; Breitenfaltung als NFKC nur für U+FF01–U+FFEF |
+| `src/zip.ts` | `Persistence/TopologyFLSArchive.swift` (Fehler, Grenzen, Pfadregeln, ZIP-Leser/-Schreiber, CRC-32) | übertragen; DEFLATE über `fflate`, mit Apples Abschneide-Verhalten nachgebildet; Pfadfaltung (NFC, Breite, volles Case-Folding) an 41 Paaren gegen das Swift-Orakel gemessen |
 | `src/archive.ts` | ebenda, Archiv-Teil von Import und Export | übertragen, ohne die XML-Ebene |
 | `test/zip.test.ts` | `TopologyProjectPersistenceTests.swift` (Archiv-Ablehnungstests, `makeMinimalZIP`, `makePayloadZIP`) | übertragen, ergänzt um DEFLATE-Grenzfälle |
 | `test/corpus.test.ts` | — | neu: 23 Korpus-Dateien, gegengeprüft mit `fflate.unzipSync` |
+| `test/pathFolding.test.ts`, `test/path-folding.*.json` | — | neu: welche Pfade dieselbe Datei meinen, Ergebnis aus dem Swift-Kern |
 
 ## tools/swift-oracle
 
diff --git a/packages/fls/src/zip.ts b/packages/fls/src/zip.ts
index ed989bb..1bf0f65 100644
--- a/packages/fls/src/zip.ts
+++ b/packages/fls/src/zip.ts
@@ -112,21 +112,39 @@ export function validateEntryPath(path: string): void {
 }
 
 /**
- * Folds full-width and half-width forms (U+FF01…U+FFEF) to their ordinary
- * counterparts — the part of NFKC that Foundation's `.widthInsensitive` does.
+ * Foundation's `.widthInsensitive`: the Halfwidth and Fullwidth Forms block
+ * (U+FF01…U+FFEE) folds to its NFKC form — full-width ASCII, half-width
+ * katakana, half-width hangul (to conjoining jamo) and the symbols. Measured
+ * against the Swift core (packages/fls/test/path-folding.*.json).
  */
 function foldWidth(text: string): string {
-  return text.replace(/[！-￯]/g, (character) => character.normalize('NFKC'));
+  return text.replace(/[\uFF01-\uFFEE]/g, (character) => character.normalize('NFKC'));
+}
+
+/**
+ * Unicode full case folding, which JavaScript lacks: lower, upper, lower per
+ * character gives it (`ß` → `ss`, `fi` → `fi`, `K` (Kelvin) → `k`, `ς` → `σ`,
+ * `İ` → `i̇`). The one exception is `ı`, which default case folding leaves
+ * alone and the round trip would turn into `i`.
+ */
+function foldCase(text: string): string {
+  let folded = '';
+  for (const character of text) {
+    folded += character === '\u0131' ? character : character.toLowerCase().toUpperCase().toLowerCase();
+  }
+  return folded;
 }
 
 /**
  * The key two paths share when they would name the same file on a case- and
- * width-insensitive file system: NFC, width-folded, case-folded, per component.
+ * width-insensitive file system: NFC, then width and case folding, per
+ * component — `precomposedStringWithCanonicalMapping.folding([.caseInsensitive,
+ * .widthInsensitive])` in Swift.
  */
 export function canonicalEntryKey(path: string): string {
   return path
     .split('/')
-    .map((component) => foldWidth(component.normalize('NFC')).toLowerCase())
+    .map((component) => foldCase(foldWidth(component.normalize('NFC'))))
     .join('/');
 }
 
diff --git a/packages/fls/test/path-folding.cases.json b/packages/fls/test/path-folding.cases.json
new file mode 100644
index 0000000..d426c51
--- /dev/null
+++ b/packages/fls/test/path-folding.cases.json
@@ -0,0 +1,207 @@
+[
+  {
+    "name": "ascii case",
+    "first": "projekt/x/a.txt",
+    "second": "projekt/x/A.TXT"
+  },
+  {
+    "name": "fullwidth letter",
+    "first": "projekt/x/Ａ.txt",
+    "second": "projekt/x/A.txt"
+  },
+  {
+    "name": "fullwidth digit",
+    "first": "projekt/x/１.txt",
+    "second": "projekt/x/1.txt"
+  },
+  {
+    "name": "halfwidth katakana",
+    "first": "projekt/x/ｱ.txt",
+    "second": "projekt/x/ア.txt"
+  },
+  {
+    "name": "sharp s vs SS",
+    "first": "projekt/x/straße.txt",
+    "second": "projekt/x/STRASSE.txt"
+  },
+  {
+    "name": "sharp s vs ss",
+    "first": "projekt/x/straße.txt",
+    "second": "projekt/x/strasse.txt"
+  },
+  {
+    "name": "capital sharp s",
+    "first": "projekt/x/ẞ.txt",
+    "second": "projekt/x/ß.txt"
+  },
+  {
+    "name": "kelvin sign",
+    "first": "projekt/x/K.txt",
+    "second": "projekt/x/k.txt"
+  },
+  {
+    "name": "angstrom sign",
+    "first": "projekt/x/Å.txt",
+    "second": "projekt/x/å.txt"
+  },
+  {
+    "name": "ohm sign",
+    "first": "projekt/x/Ω.txt",
+    "second": "projekt/x/ω.txt"
+  },
+  {
+    "name": "fi ligature",
+    "first": "projekt/x/fi.txt",
+    "second": "projekt/x/fi.txt"
+  },
+  {
+    "name": "composed vs decomposed",
+    "first": "projekt/x/é.txt",
+    "second": "projekt/x/é.txt"
+  },
+  {
+    "name": "dotted capital I",
+    "first": "projekt/x/İ.txt",
+    "second": "projekt/x/i.txt"
+  },
+  {
+    "name": "dotless i",
+    "first": "projekt/x/ı.txt",
+    "second": "projekt/x/I.txt"
+  },
+  {
+    "name": "final sigma",
+    "first": "projekt/x/ς.txt",
+    "second": "projekt/x/σ.txt"
+  },
+  {
+    "name": "micro sign",
+    "first": "projekt/x/µ.txt",
+    "second": "projekt/x/μ.txt"
+  },
+  {
+    "name": "circled letter",
+    "first": "projekt/x/Ⓐ.txt",
+    "second": "projekt/x/ⓐ.txt"
+  },
+  {
+    "name": "superscript two",
+    "first": "projekt/x/².txt",
+    "second": "projekt/x/2.txt"
+  },
+  {
+    "name": "ideographic space",
+    "first": "projekt/x/a　b.txt",
+    "second": "projekt/x/a b.txt"
+  },
+  {
+    "name": "umlaut case",
+    "first": "projekt/x/Ä.txt",
+    "second": "projekt/x/ä.txt"
+  },
+  {
+    "name": "fullwidth tilde",
+    "first": "projekt/x/～.txt",
+    "second": "projekt/x/~.txt"
+  },
+  {
+    "name": "halfwidth hangul",
+    "first": "projekt/x/ﾡ.txt",
+    "second": "projekt/x/ㄱ.txt"
+  },
+  {
+    "name": "fullwidth won sign",
+    "first": "projekt/x/￦.txt",
+    "second": "projekt/x/₩.txt"
+  },
+  {
+    "name": "different names",
+    "first": "projekt/x/a.txt",
+    "second": "projekt/x/b.txt"
+  },
+  {
+    "name": "halfwidth left arrow",
+    "first": "projekt/x/￩.txt",
+    "second": "projekt/x/←.txt"
+  },
+  {
+    "name": "halfwidth forms light vertical",
+    "first": "projekt/x/￨.txt",
+    "second": "projekt/x/│.txt"
+  },
+  {
+    "name": "halfwidth katakana middle dot",
+    "first": "projekt/x/･.txt",
+    "second": "projekt/x/・.txt"
+  },
+  {
+    "name": "halfwidth hangul filler",
+    "first": "projekt/x/ﾠ.txt",
+    "second": "projekt/x/ㅤ.txt"
+  },
+  {
+    "name": "halfwidth hangul last",
+    "first": "projekt/x/ￜ.txt",
+    "second": "projekt/x/ㅣ.txt"
+  },
+  {
+    "name": "fullwidth cent sign",
+    "first": "projekt/x/￠.txt",
+    "second": "projekt/x/¢.txt"
+  },
+  {
+    "name": "long s",
+    "first": "projekt/x/ſ.txt",
+    "second": "projekt/x/s.txt"
+  },
+  {
+    "name": "capital sharp s vs ss",
+    "first": "projekt/x/ẞ.txt",
+    "second": "projekt/x/ss.txt"
+  },
+  {
+    "name": "ff ligature",
+    "first": "projekt/x/ff.txt",
+    "second": "projekt/x/ff.txt"
+  },
+  {
+    "name": "dotless i vs i",
+    "first": "projekt/x/ı.txt",
+    "second": "projekt/x/i.txt"
+  },
+  {
+    "name": "dotted capital I vs i dot",
+    "first": "projekt/x/İ.txt",
+    "second": "projekt/x/i̇.txt"
+  },
+  {
+    "name": "greek iota with dialytika and tonos",
+    "first": "projekt/x/ΐ.txt",
+    "second": "projekt/x/ΐ.txt"
+  },
+  {
+    "name": "cherokee small letter",
+    "first": "projekt/x/ꭰ.txt",
+    "second": "projekt/x/Ꭰ.txt"
+  },
+  {
+    "name": "fullwidth lower vs ascii upper",
+    "first": "projekt/x/ａ.txt",
+    "second": "projekt/x/A.txt"
+  },
+  {
+    "name": "halfwidth hangul vs its NFKC form",
+    "first": "projekt/x/ﾡ.txt",
+    "second": "projekt/x/ᄀ.txt"
+  },
+  {
+    "name": "halfwidth hangul filler vs its NFKC form",
+    "first": "projekt/x/ﾠ.txt",
+    "second": "projekt/x/ᅠ.txt"
+  },
+  {
+    "name": "halfwidth hangul last vs its NFKC form",
+    "first": "projekt/x/ￜ.txt",
+    "second": "projekt/x/ᅵ.txt"
+  }
+]
diff --git a/packages/fls/test/path-folding.swift.json b/packages/fls/test/path-folding.swift.json
new file mode 100644
index 0000000..608eb18
--- /dev/null
+++ b/packages/fls/test/path-folding.swift.json
@@ -0,0 +1,166 @@
+[
+  {
+    "name" : "ascii case",
+    "outcome" : "collide"
+  },
+  {
+    "name" : "fullwidth letter",
+    "outcome" : "collide"
+  },
+  {
+    "name" : "fullwidth digit",
+    "outcome" : "collide"
+  },
+  {
+    "name" : "halfwidth katakana",
+    "outcome" : "collide"
+  },
+  {
+    "name" : "sharp s vs SS",
+    "outcome" : "collide"
+  },
+  {
+    "name" : "sharp s vs ss",
+    "outcome" : "collide"
+  },
+  {
+    "name" : "capital sharp s",
+    "outcome" : "collide"
+  },
+  {
+    "name" : "kelvin sign",
+    "outcome" : "collide"
+  },
+  {
+    "name" : "angstrom sign",
+    "outcome" : "collide"
+  },
+  {
+    "name" : "ohm sign",
+    "outcome" : "collide"
+  },
+  {
+    "name" : "fi ligature",
+    "outcome" : "collide"
+  },
+  {
+    "name" : "composed vs decomposed",
+    "outcome" : "sameKey"
+  },
+  {
+    "name" : "dotted capital I",
+    "outcome" : "distinct"
+  },
+  {
+    "name" : "dotless i",
+    "outcome" : "distinct"
+  },
+  {
+    "name" : "final sigma",
+    "outcome" : "collide"
+  },
+  {
+    "name" : "micro sign",
+    "outcome" : "collide"
+  },
+  {
+    "name" : "circled letter",
+    "outcome" : "collide"
+  },
+  {
+    "name" : "superscript two",
+    "outcome" : "distinct"
+  },
+  {
+    "name" : "ideographic space",
+    "outcome" : "distinct"
+  },
+  {
+    "name" : "umlaut case",
+    "outcome" : "collide"
+  },
+  {
+    "name" : "fullwidth tilde",
+    "outcome" : "collide"
+  },
+  {
+    "name" : "halfwidth hangul",
+    "outcome" : "distinct"
+  },
+  {
+    "name" : "fullwidth won sign",
+    "outcome" : "collide"
+  },
+  {
+    "name" : "different names",
+    "outcome" : "distinct"
+  },
+  {
+    "name" : "halfwidth left arrow",
+    "outcome" : "collide"
+  },
+  {
+    "name" : "halfwidth forms light vertical",
+    "outcome" : "collide"
+  },
+  {
+    "name" : "halfwidth katakana middle dot",
+    "outcome" : "collide"
+  },
+  {
+    "name" : "halfwidth hangul filler",
+    "outcome" : "distinct"
+  },
+  {
+    "name" : "halfwidth hangul last",
+    "outcome" : "distinct"
+  },
+  {
+    "name" : "fullwidth cent sign",
+    "outcome" : "collide"
+  },
+  {
+    "name" : "long s",
+    "outcome" : "collide"
+  },
+  {
+    "name" : "capital sharp s vs ss",
+    "outcome" : "collide"
+  },
+  {
+    "name" : "ff ligature",
+    "outcome" : "collide"
+  },
+  {
+    "name" : "dotless i vs i",
+    "outcome" : "distinct"
+  },
+  {
+    "name" : "dotted capital I vs i dot",
+    "outcome" : "collide"
+  },
+  {
+    "name" : "greek iota with dialytika and tonos",
+    "outcome" : "sameKey"
+  },
+  {
+    "name" : "cherokee small letter",
+    "outcome" : "collide"
+  },
+  {
+    "name" : "fullwidth lower vs ascii upper",
+    "outcome" : "collide"
+  },
+  {
+    "name" : "halfwidth hangul vs its NFKC form",
+    "outcome" : "collide"
+  },
+  {
+    "name" : "halfwidth hangul filler vs its NFKC form",
+    "outcome" : "collide"
+  },
+  {
+    "name" : "halfwidth hangul last vs its NFKC form",
+    "outcome" : "collide"
+  }
+]
diff --git a/packages/fls/test/pathFolding.test.ts b/packages/fls/test/pathFolding.test.ts
new file mode 100644
index 0000000..6a0c8db
--- /dev/null
+++ b/packages/fls/test/pathFolding.test.ts
@@ -0,0 +1,52 @@
+// Which archive paths name the same file: the TypeScript folding against what
+// the Swift core decides for the same pairs (path-folding.swift.json, written
+// by tools/swift-oracle/run.sh; the Swift folding is Linux Foundation's).
+
+import { readFileSync } from 'node:fs';
+import { dirname, join } from 'node:path';
+import { fileURLToPath } from 'node:url';
+import { describe, expect, it } from 'vitest';
+import { FlsArchiveError, writeZipEntries } from '../src/index.js';
+
+const here = dirname(fileURLToPath(import.meta.url));
+const cases = JSON.parse(readFileSync(join(here, 'path-folding.cases.json'), 'utf8')) as {
+  name: string;
+  first: string;
+  second: string;
+}[];
+const swift = new Map(
+  (JSON.parse(readFileSync(join(here, 'path-folding.swift.json'), 'utf8')) as { name: string; outcome: string }[]).map(
+    (item) => [item.name, item.outcome],
+  ),
+);
+
+function outcome(first: string, second: string): string {
+  try {
+    writeZipEntries(
+      new Map([
+        [first, Uint8Array.of(1)],
+        [second, Uint8Array.of(2)],
+      ]),
+    );
+    return 'distinct';
+  } catch (error) {
+    if (error instanceof FlsArchiveError) return error.code === 'duplicateEntry' ? 'collide' : error.code;
+    throw error;
+  }
+}
+
+describe('archive path folding matches Swift', () => {
+  it('has a Swift result for every case', () => {
+    expect(cases.every((item) => swift.has(item.name))).toBe(true);
+  });
+
+  for (const item of cases) {
+    it(item.name, () => {
+      // Swift strings compare by canonical equivalence, so a composed and a
+      // decomposed spelling are one dictionary key there ("sameKey"). A Map
+      // here keeps both — and the writer then refuses them as one file.
+      const expected = swift.get(item.name) === 'sameKey' ? 'collide' : swift.get(item.name);
+      expect(outcome(item.first, item.second)).toBe(expected);
+    });
+  }
+});
diff --git a/tools/swift-oracle/Sources/Oracle/main.swift b/tools/swift-oracle/Sources/Oracle/main.swift
index 5037862..c498b3a 100644
--- a/tools/swift-oracle/Sources/Oracle/main.swift
+++ b/tools/swift-oracle/Sources/Oracle/main.swift
@@ -291,8 +291,47 @@ func readCorpus(root: URL) throws -> JSON {
     return result
 }
 
+// MARK: - Archive path folding
+
+struct PathCase: Decodable { let name: String; let first: String; let second: String }
+
+/// Whether Swift's archive writer treats two entry paths as the same file.
+/// The folding itself is file-private in Swift; the export reports it as a
+/// duplicate entry when two carried entries collide.
+func foldPaths(_ cases: [PathCase]) -> [JSON] {
+    cases.map { item in
+        var result: JSON = ["name": item.name]
+        // Swift compares strings by canonical equivalence: "é" and "e\u{301}"
+        // are one dictionary key, so they never reach the archive writer.
+        if item.first == item.second {
+            result["outcome"] = "sameKey"
+            return result
+        }
+        do {
+            _ = try TopologyProjectStore.exportFiliusArchiveWithReport(
+                from: TopologyEditorState(),
+                supplementalEntries: [item.first: Data("1".utf8), item.second: Data("2".utf8)]
+            )
+            result["outcome"] = "distinct"
+        } catch let error as TopologyFLSArchiveError {
+            result["outcome"] = error.code == .duplicateEntry ? "collide" : error.code.rawValue
+        } catch {
+            result["outcome"] = "error: \(error)"
+        }
+        return result
+    }
+}
+
 // MARK: - Main
 
+if CommandLine.arguments.count == 4, CommandLine.arguments[1] == "--path-folding" {
+    let cases = try JSONDecoder().decode([PathCase].self, from: Data(contentsOf: URL(fileURLWithPath: CommandLine.arguments[2])))
+    let data = try JSONSerialization.data(withJSONObject: foldPaths(cases), options: [.prettyPrinted, .sortedKeys])
+    try (data + Data("\n".utf8)).write(to: URL(fileURLWithPath: CommandLine.arguments[3]))
+    print("path folding: \(cases.count) cases")
+    exit(0)
+}
+
 if CommandLine.arguments.count == 4, CommandLine.arguments[1] == "--corpus" {
     let summary = try readCorpus(root: URL(fileURLWithPath: CommandLine.arguments[2]))
     let data = try JSONSerialization.data(withJSONObject: summary, options: [.prettyPrinted, .sortedKeys])
diff --git a/tools/swift-oracle/core.209 b/tools/swift-oracle/core.209
new file mode 100644
index 0000000..05c4fb8
Binary files /dev/null and b/tools/swift-oracle/core.209 differ
diff --git a/tools/swift-oracle/core.7 b/tools/swift-oracle/core.7
index 7d37f31..3fa020a 100644
Binary files a/tools/swift-oracle/core.7 and b/tools/swift-oracle/core.7 differ
diff --git a/tools/swift-oracle/run.sh b/tools/swift-oracle/run.sh
index a2df364..92e15e0 100755
--- a/tools/swift-oracle/run.sh
+++ b/tools/swift-oracle/run.sh
@@ -11,4 +11,5 @@ docker run --rm -v "$root:/work" -w /work/tools/swift-oracle swift:6.1-jammy sh
     set -e
     swift build -q
     .build/debug/Oracle /work/packages/core/test/scenarios
-    .build/debug/Oracle --corpus /work/corpus /work/corpus/corpus.swift.json'
+    .build/debug/Oracle --corpus /work/corpus /work/corpus/corpus.swift.json
+    .build/debug/Oracle --path-folding /work/packages/fls/test/path-folding.cases.json /work/packages/fls/test/path-folding.swift.json'