feat(worker): CRC32 archive fingerprint compare

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

worker/src/archive/fingerprint.test.ts

@@ -1,7 +1,35 @@
 import { describe, it, expect } from "vitest";
+import { crcFingerprint, fingerprintsMatch } from "./fingerprint.js";
+import type { FileEntry } from "./zip-reader.js";
 
-describe("harness", () => {
-  it("runs", () => {
-    expect(1 + 1).toBe(2);
+const fe = (crc: string | null): FileEntry => ({
+  path: "a", fileName: "a", extension: null,
+  compressedSize: 0n, uncompressedSize: 0n, crc32: crc,
+});
+
+describe("crcFingerprint", () => {
+  it("sorts crcs and marks complete", () => {
+    expect(crcFingerprint([fe("00ff"), fe("00aa")])).toEqual({ crcs: ["00aa", "00ff"], complete: true });
+  });
+  it("is incomplete when any crc is null", () => {
+    expect(crcFingerprint([fe("00aa"), fe(null)]).complete).toBe(false);
+  });
+  it("is incomplete when empty", () => {
+    expect(crcFingerprint([]).complete).toBe(false);
+  });
+});
+
+describe("fingerprintsMatch", () => {
+  it("matches identical crc multisets regardless of order", () => {
+    expect(fingerprintsMatch([fe("01"), fe("02")], [fe("02"), fe("01")])).toBe(true);
+  });
+  it("rejects different counts", () => {
+    expect(fingerprintsMatch([fe("01")], [fe("01"), fe("02")])).toBe(false);
+  });
+  it("rejects disjoint sets", () => {
+    expect(fingerprintsMatch([fe("01")], [fe("09")])).toBe(false);
+  });
+  it("rejects when either side is incomplete", () => {
+    expect(fingerprintsMatch([fe("01"), fe(null)], [fe("01"), fe("02")])).toBe(false);
   });
 });

worker/src/archive/fingerprint.ts

@@ -0,0 +1,21 @@
+import type { FileEntry } from "./zip-reader.js";
+
+export function crcFingerprint(entries: FileEntry[]): { crcs: string[]; complete: boolean } {
+  if (entries.length === 0) return { crcs: [], complete: false };
+  const crcs: string[] = [];
+  let complete = true;
+  for (const e of entries) {
+    if (e.crc32 == null) { complete = false; continue; }
+    crcs.push(e.crc32.toLowerCase());
+  }
+  crcs.sort();
+  return { crcs, complete };
+}
+
+export function fingerprintsMatch(a: FileEntry[], b: FileEntry[]): boolean {
+  const fa = crcFingerprint(a);
+  const fb = crcFingerprint(b);
+  if (!fa.complete || !fb.complete) return false;
+  if (fa.crcs.length !== fb.crcs.length) return false;
+  return fa.crcs.every((c, i) => c === fb.crcs[i]);
+}