feat(worker): derive a dedup identity for forward-path packages without bytes

worker/src/archive/forward-identity.ts

@@ -0,0 +1,33 @@
+import { createHash } from "crypto";
+import { crcFingerprint } from "./fingerprint.js";
+import type { FileEntry } from "./zip-reader.js";
+
+/**
+ * Derive a Package.contentHash-compatible identity string for a forward-path
+ * package (no downloaded bytes exist to hash directly). Priority order:
+ *   1. A CRC32-fingerprint hash, when the ranged listing's CRCs are complete
+ *      (ZIP/RAR today) — the strongest available signal, since it lets
+ *      forward-path and download-path copies of the same archive still
+ *      collide/dedupe on identical content.
+ *   2. TDLib's remote.unique_id, when CRCs are incomplete (7z today has none).
+ *   3. sourceChannelId+sourceMessageId, as a last-resort unique value so the
+ *      required-unique Package.contentHash column is always satisfiable.
+ * Follows the same `<prefix>:<value>` synthetic-hash convention already used
+ * by `rebuild.ts`'s `rebuild:${destChannelId}:${destMessageId}` placeholder.
+ */
+export function deriveForwardContentHash(
+  entries: FileEntry[],
+  remoteUniqueId: string | null,
+  sourceChannelId: string,
+  sourceMessageId: bigint,
+): string {
+  const fp = crcFingerprint(entries);
+  if (fp.complete && fp.crcs.length > 0) {
+    const hash = createHash("sha256").update(fp.crcs.join(",")).digest("hex");
+    return `fingerprint:${hash}`;
+  }
+  if (remoteUniqueId) {
+    return `forward:${remoteUniqueId}`;
+  }
+  return `forward:${sourceChannelId}:${sourceMessageId}`;
+}