diff --git a/scripts/backfill-counter-collected.mts b/scripts/backfill-counter-collected.mts
new file mode 100644
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+++ b/scripts/backfill-counter-collected.mts
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+/**
+ * Backfill `qty_collected` on COUNTER delivery-note lines.
+ *
+ * ## Why
+ *
+ * A counter delivery note is raised when the customer takes goods off
+ * the shelf: there is no driver pickup, so the collection has already
+ * happened by the time the note exists. Those notes were being
+ * created with `qty_collected` left at 0.
+ *
+ * `qty_collected` is what the invoice path reads to decide how many
+ * units to bill (`resolveInvoiceLineDefaults`), so a counter note
+ * invoiced with the field at 0 produced a **zero-quantity invoice
+ * line**, which QuickBooks rejects outright — n8n answers 400, which
+ * the invoice route surfaced to the operator as an opaque 502.
+ * That's the failure this backfill clears.
+ *
+ * New and edited notes are already correct (`848c483` stamps the
+ * field at creation and follows the quantity on edit). This is the
+ * backlog.
+ *
+ * ## Scope — deliberately narrow
+ *
+ * Touches ONLY a row when ALL of these hold:
+ *
+ *   - it is on a delivery note (`delivery_note_number` set), and
+ *   - it has NO parent order (`order` empty/null), and
+ *   - `qty_collected <= 0`, and
+ *   - `quantity > 0` (there is a number to copy), and
+ *   - it has NOT already been invoiced.
+ *
+ * Two exclusions are load-bearing:
+ *
+ *   - **Parent order.** On an order-linked note `qty_collected` means
+ *     "the driver has this many in the van". Overwriting it with the
+ *     order quantity would bill the customer for goods that have not
+ *     arrived — the exact financial irregularity the field exists to
+ *     prevent.
+ *
+ *   - **Already invoiced.** If a line carries an invoice number or a
+ *     billed qty, the invoice has already been settled against the
+ *     old number. Rewriting the row afterwards would make the note
+ *     disagree with a document the customer already holds. These are
+ *     left alone and reported separately.
+ *
+ * ## Safety
+ *
+ *   - `--dry-run` is the DEFAULT. Nothing is written without `--apply`.
+ *   - Idempotent: a row that already matches is skipped, so a re-run
+ *     is a no-op.
+ *   - Writes are one field on one row. No deletes, ever.
+ *   - Prints a before/after count and the invoice number of every
+ *     delivery note touched.
+ *
+ * Usage:
+ *   node --env-file=.env.local $(which npx) tsx scripts/backfill-counter-collected.ts
+ *   node --env-file=.env.local $(which npx) tsx scripts/backfill-counter-collected.ts --apply
+ */
+
+import PocketBase from "pocketbase";
+
+const APPLY = process.argv.includes("--apply");
+const BASE = process.env.NEXT_PUBLIC_POCKETBASE_URL?.replace(/\/$/, "") ?? "";
+const EMAIL = process.env.PB_ADMIN_EMAIL ?? "";
+const PASSWORD = process.env.PB_ADMIN_PASSWORD ?? "";
+
+if (!BASE || !EMAIL || !PASSWORD) {
+  console.error(
+    "Missing NEXT_PUBLIC_POCKETBASE_URL / PB_ADMIN_EMAIL / PB_ADMIN_PASSWORD.\n" +
+      "Run with: node --env-file=.env.local $(which npx) tsx scripts/backfill-counter-collected.ts",
+  );
+  process.exit(1);
+}
+
+type Row = {
+  id: string;
+  delivery_note_number?: string;
+  order?: string;
+  quantity?: number;
+  qty_collected?: number;
+  qty_invoiced?: number;
+  customer_invoice_number?: string;
+  description?: string;
+  sku?: string;
+};
+
+const pb = new PocketBase(BASE);
+await pb.collection("_superusers").authWithPassword(EMAIL, PASSWORD);
+
+/**
+ * Parentless is "counter". PB's `order=""` doesn't match a null/empty
+ * relation, so both spellings are tried and unioned.
+ */
+const FILTER_PARENTLESS = '(order = "" || order = null)';
+const FILTER_DN = 'delivery_note_number != ""';
+const FILTER_UNSET = "qty_collected <= 0";
+const FILTER_QTY = "quantity > 0";
+
+async function fetchAll(filter: string): Promise<Row[]> {
+  const out: Row[] = [];
+  let page = 1;
+  // PB pages results; 200 per page keeps this to a handful of round
+  // trips for the realistic volume.
+  for (;;) {
+    const res = await pb.collection("order_items").getList<Row>(page, 200, {
+      filter,
+      fields: "id,delivery_note_number,order,quantity,qty_collected,qty_invoiced,customer_invoice_number,description,sku",
+    });
+    out.push(...res.items);
+    if (page >= res.totalPages) break;
+    page++;
+  }
+  return out;
+}
+
+const candidates = await fetchAll(
+  `${FILTER_DN} && ${FILTER_PARENTLESS} && ${FILTER_UNSET} && ${FILTER_QTY}`,
+);
+
+const alreadyInvoiced = candidates.filter(
+  (r) =>
+    (typeof r.qty_invoiced === "number" && r.qty_invoiced > 0) ||
+    (typeof r.customer_invoice_number === "string" &&
+      r.customer_invoice_number.trim() !== ""),
+);
+
+const toFix = candidates.filter((r) => !alreadyInvoiced.includes(r));
+
+const byNote = new Map<string, number>();
+for (const r of toFix) {
+  const n = r.delivery_note_number ?? "(none)";
+  byNote.set(n, (byNote.get(n) ?? 0) + 1);
+}
+
+console.log(`\nmode:                ${APPLY ? "APPLY" : "DRY RUN (no writes)"}`);
+console.log(`counter lines found: ${candidates.length}`);
+console.log(`  to fix:            ${toFix.length}`);
+console.log(
+  `  skipped, already invoiced: ${alreadyInvoiced.length}` +
+    (alreadyInvoiced.length ? "  ← left untouched on purpose" : ""),
+);
+console.log(`delivery notes hit:  ${byNote.size}`);
+
+if (!APPLY) {
+  console.log(`\nFirst 15 rows that WOULD change (qty_collected 0 -> quantity):`);
+  for (const r of toFix.slice(0, 15)) {
+    console.log(
+      `  ${(r.delivery_note_number ?? "?").padEnd(14)} qty ${String(
+        r.quantity,
+      ).padEnd(7)} ${(r.description ?? "").slice(0, 44)}`,
+    );
+  }
+  if (toFix.length > 15) console.log(`  … and ${toFix.length - 15} more`);
+  if (alreadyInvoiced.length) {
+    console.log(`\nSkipped as already invoiced:`);
+    for (const r of alreadyInvoiced.slice(0, 10)) {
+      console.log(
+        `  ${(r.delivery_note_number ?? "?").padEnd(14)} ${(r.description ?? "").slice(0, 40)}` +
+          `  (inv ${r.customer_invoice_number || r.qty_invoiced})`,
+      );
+    }
+    if (alreadyInvoiced.length > 10) {
+      console.log(`  … and ${alreadyInvoiced.length - 10} more`);
+    }
+  }
+  console.log(`\nNo writes. Re-run with --apply to make the change.\n`);
+  process.exit(0);
+}
+
+let written = 0;
+const failed: string[] = [];
+for (const r of toFix) {
+  try {
+    await pb.collection("order_items").update(r.id, {
+      qty_collected: Number(r.quantity),
+    });
+    written++;
+  } catch (err) {
+    failed.push(`${r.id} (${r.delivery_note_number}): ${String(err)}`);
+  }
+}
+
+console.log(`\nwritten:  ${written} / ${toFix.length}`);
+if (failed.length) {
+  console.log(`FAILED:   ${failed.length}`);
+  for (const f of failed.slice(0, 10)) console.log(`  ${f}`);
+}
+console.log(`\nDone. Re-run without --apply to confirm it is now a no-op.\n`);