feat(worker): DB helpers for provenance backfill

Adds findPlaceholderCandidate, getPackageFileCrcs, and
backfillProvenance to worker/src/db/queries.ts (Task 5). Candidate
predicate matches placeholder packages by source==dest or the
sourceMessageId==0 rebuild sentinel; backfillProvenance re-checks
placeholder status inside the transaction before overwriting fields.

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

worker/src/db/queries.ts

@@ -1,5 +1,6 @@
 import { db } from "./client.js";
 import type { ArchiveType, FetchStatus } from "@prisma/client";
+import type { FileEntry } from "../archive/zip-reader.js";
 
 export async function getActiveAccounts() {
   return db.telegramAccount.findMany({
@@ -1005,3 +1006,91 @@ export async function createAutoGroup(input: {
 
   return group.id;
 }
+
+// ── Provenance backfill ──
+
+export async function findPlaceholderCandidate(
+  destChannelId: string,
+  fileName: string,
+  fileSize: bigint,
+): Promise<{ id: string; archiveType: string; fileCount: number } | null> {
+  return db.package.findFirst({
+    where: {
+      fileName,
+      fileSize,
+      destMessageId: { not: null },
+      // Placeholder provenance (spec §1): manual-upload (source == destination)
+      // OR rebuild record (sourceMessageId == 0 "unknown" sentinel).
+      OR: [
+        { sourceChannelId: destChannelId },
+        { sourceMessageId: 0n },
+      ],
+    },
+    select: { id: true, archiveType: true, fileCount: true },
+    orderBy: { indexedAt: "asc" },
+  });
+}
+
+export async function getPackageFileCrcs(packageId: string): Promise<(string | null)[]> {
+  const rows = await db.packageFile.findMany({
+    where: { packageId },
+    select: { crc32: true },
+  });
+  return rows.map((r) => r.crc32);
+}
+
+export interface BackfillProvenanceInput {
+  packageId: string;
+  destChannelId: string; // to re-check placeholder status in-txn
+  sourceChannelId: string;
+  sourceMessageId: bigint;
+  sourceTopicId: bigint | null;
+  sourceCaption: string | null;
+  remoteUniqueId: string | null;
+  creator: string | null; // always set (re-derived by caller)
+  entries?: FileEntry[]; // set only if candidate had fileCount === 0
+  previewData?: Buffer | null; // set only if provided and candidate lacks one
+  previewMsgId?: bigint | null;
+}
+
+export async function backfillProvenance(input: BackfillProvenanceInput): Promise<boolean> {
+  return db.$transaction(async (tx) => {
+    const current = await tx.package.findUnique({
+      where: { id: input.packageId },
+      select: { sourceChannelId: true, sourceMessageId: true, previewData: true, fileCount: true },
+    });
+    // Re-check placeholder status inside the txn (another worker may have won).
+    // Placeholder = manual-upload (source==dest) OR rebuild (sourceMessageId==0).
+    const stillPlaceholder =
+      !!current &&
+      (current.sourceChannelId === input.destChannelId || current.sourceMessageId === 0n);
+    if (!stillPlaceholder) return false;
+
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    const data: any = {
+      sourceChannelId: input.sourceChannelId,
+      sourceMessageId: input.sourceMessageId,
+      sourceTopicId: input.sourceTopicId,
+      sourceCaption: input.sourceCaption,
+      remoteUniqueId: input.remoteUniqueId,
+      creator: input.creator,
+    };
+    if (input.entries && current.fileCount === 0) {
+      await tx.packageFile.deleteMany({ where: { packageId: input.packageId } });
+      await tx.packageFile.createMany({
+        data: input.entries.map((e) => ({
+          packageId: input.packageId,
+          path: e.path, fileName: e.fileName, extension: e.extension,
+          compressedSize: e.compressedSize, uncompressedSize: e.uncompressedSize, crc32: e.crc32,
+        })),
+      });
+      data.fileCount = input.entries.length;
+    }
+    if (input.previewData && !current.previewData) {
+      data.previewData = input.previewData;
+      data.previewMsgId = input.previewMsgId ?? null;
+    }
+    await tx.package.update({ where: { id: input.packageId }, data });
+    return true;
+  });
+}