feat(worker): cross-channel CRC-fingerprint repost check for the forward path

worker/src/archive/forward-repost-check.ts

@@ -0,0 +1,33 @@
+import type { Client } from "tdl";
+import type { FileEntry } from "./zip-reader.js";
+import { compareFingerprints, resolveCandidateFingerprintEntries } from "../provenance-backfill.js";
+import { findFingerprintDedupCandidates } from "../db/queries.js";
+
+export interface FingerprintRepostResult {
+  isDuplicate: boolean;
+  matchedPackageId: string | null;
+}
+
+/**
+ * Cross-channel duplicate check for the forward-priority path: compare the
+ * new archive's CRC fingerprint against every existing Package sharing its
+ * name+size, regardless of which channel or ingestion path produced them.
+ * This is what lets a forwarded copy dedupe against a previously
+ * fully-downloaded copy of the same archive, despite never sharing a
+ * byte-hash-derived contentHash.
+ */
+export async function checkFingerprintRepost(
+  client: Client,
+  entries: FileEntry[],
+  fileName: string,
+  fileSize: bigint,
+): Promise<FingerprintRepostResult> {
+  const candidates = await findFingerprintDedupCandidates(fileName, fileSize);
+  for (const candidate of candidates) {
+    const candidateEntries = await resolveCandidateFingerprintEntries(client, candidate);
+    if (compareFingerprints(entries, candidateEntries) === "match") {
+      return { isDuplicate: true, matchedPackageId: candidate.id };
+    }
+  }
+  return { isDuplicate: false, matchedPackageId: null };
+}