diff --git a/AGENTS.md b/AGENTS.md
index 9146f3c..70d0ea6 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -38,6 +38,13 @@ Pattern in code:
    stream the bytes back via PB's `/api/files/...` URL
 3. Stable filename per document type so the retrieval side can
    disambiguate from other attachments on the same item
+
+**Always ADD, never replace:** a PocketBase file PATCH under the bare
+field name replaces the whole list — it deleted a driver's photo on
+2026-10-19. Build uploads with `addAttachmentForm()` from
+`src/lib/server/order-item-files.ts` (`order_item_attachements+`, and
+`-` only for the same document's older copies), and find a file by name
+with `pickStoredCopy()`, never by position.
 <!-- END:pb-attachments-pattern -->
 
 <!-- BEGIN:file-url-paths -->
diff --git a/src/app/api/invoicing/delivery-note-pdf/route.test.ts b/src/app/api/invoicing/delivery-note-pdf/route.test.ts
index cab5173..3f1f581 100644
--- a/src/app/api/invoicing/delivery-note-pdf/route.test.ts
+++ b/src/app/api/invoicing/delivery-note-pdf/route.test.ts
@@ -83,6 +83,20 @@ describe("GET /api/invoicing/delivery-note-pdf", () => {
     );
   });
 
+  it("serves the DN PDF, not a driver photo that sits first on the line", async () => {
+    getFullListMock.mockResolvedValueOnce([
+      { id: "row-1", order_item_attachements: ["driver_photo_ab12cd34ef.jpg", "dn26071401_ta9aoxfc9s.pdf"] },
+    ]);
+    fetchMock.mockResolvedValueOnce(
+      new Response(new Uint8Array([0x25, 0x50, 0x44, 0x46]), { status: 200, headers: { "Content-Type": "application/pdf" } }),
+    );
+    const response = await GET(
+      makeRequest("https://test.local/api/invoicing/delivery-note-pdf?deliveryNoteNumber=DN26071401") as any,
+    );
+    expect(response.status).toBe(200);
+    expect(fetchMock).toHaveBeenCalledWith(expect.stringContaining("/api/files/order_items/row-1/dn26071401_ta9aoxfc9s.pdf"));
+  });
+
   it("returns 502 when the PB file fetch itself fails", async () => {
     getFullListMock.mockResolvedValueOnce([
       { id: "row-1", order_item_attachements: "token.pdf" },
diff --git a/src/app/api/invoicing/delivery-note-pdf/route.ts b/src/app/api/invoicing/delivery-note-pdf/route.ts
index 86971f5..03a5d41 100644
--- a/src/app/api/invoicing/delivery-note-pdf/route.ts
+++ b/src/app/api/invoicing/delivery-note-pdf/route.ts
@@ -1,3 +1,4 @@
+import { attachmentList, pickStoredCopy } from "@/lib/server/order-item-files";
 import { NextRequest, NextResponse } from "next/server";
 
 import { getAdminPocketBase } from "@/lib/server/pocketbase-admin";
@@ -40,7 +41,15 @@ function readStringField(value: unknown, key: string): string {
  */
 function findDeliveryNoteAttachmentToken(
   items: OrderItemRecord[],
+  deliveryNoteNumber: string,
 ): { itemId: string; token: string } | null {
+  // By name first: the line also carries the driver's photo and any
+  // supplier invoice, so "the first file" isn't necessarily the DN.
+  for (const item of items) {
+    const token = pickStoredCopy(attachmentList(item.order_item_attachements), `${deliveryNoteNumber}.pdf`);
+    if (token) return { itemId: item.id, token };
+  }
+  // Legacy: older DNs were stored under other names, alone on the line.
   for (const item of items) {
     const raw = item.order_item_attachements;
     if (typeof raw === "string" && raw.length > 0) {
@@ -71,7 +80,7 @@ async function handleRetrieve(input: { deliveryNoteNumber: string }) {
         { status: 404 },
       );
     }
-    const found = findDeliveryNoteAttachmentToken(items);
+    const found = findDeliveryNoteAttachmentToken(items, deliveryNoteNumber);
     if (!found) {
       return NextResponse.json(
         { error: "No saved PDF for this delivery note" },
diff --git a/src/app/api/invoicing/delivery-note/route.test.ts b/src/app/api/invoicing/delivery-note/route.test.ts
index f31ad34..42d8078 100644
--- a/src/app/api/invoicing/delivery-note/route.test.ts
+++ b/src/app/api/invoicing/delivery-note/route.test.ts
@@ -195,7 +195,9 @@ describe("POST /api/invoicing/delivery-note", () => {
     expect(formCalls.length).toBe(2);
     for (const call of formCalls) {
       const form = call[1] as FormData;
-      const entry = form.get("order_item_attachements");
+      // "+" adds: the driver's photo and supplier invoice on the line stay.
+      expect(form.get("order_item_attachements")).toBeNull();
+      const entry = form.get("order_item_attachements+");
       expect(entry).toBeDefined();
       // FormData entries can be string | File. We expect a File
       // (the PDF blob uploaded under the canonical name).
diff --git a/src/app/api/invoicing/delivery-note/route.ts b/src/app/api/invoicing/delivery-note/route.ts
index 5dbeb34..8ba569d 100644
--- a/src/app/api/invoicing/delivery-note/route.ts
+++ b/src/app/api/invoicing/delivery-note/route.ts
@@ -1,3 +1,4 @@
+import { addAttachmentForm, attachmentList } from "@/lib/server/order-item-files";
 import { NextRequest, NextResponse } from "next/server";
 
 import { getAdminPocketBase } from "@/lib/server/pocketbase-admin";
@@ -473,8 +474,7 @@ async function uploadDeliveryNotePdf(
   const blob = new Blob([new Uint8Array(pdfBuffer)], { type: "application/pdf" });
   await Promise.all(
     items.map(async (item) => {
-      const form = new FormData();
-      form.append("order_item_attachements", blob, filename);
+      const form = addAttachmentForm(blob, filename, attachmentList(item.order_item_attachements));
       await pb.collection("order_items").update(item.id, form);
     }),
   );
diff --git a/src/lib/server/collection-confirm-service.ts b/src/lib/server/collection-confirm-service.ts
index e2adb54..9c7c957 100644
--- a/src/lib/server/collection-confirm-service.ts
+++ b/src/lib/server/collection-confirm-service.ts
@@ -1,3 +1,4 @@
+import { addAttachmentForm } from "@/lib/server/order-item-files";
 import { getAdminPocketBase } from "@/lib/server/pocketbase-admin";
 import { getOrderItemsCollectionName } from "@/lib/server/orders-service";
 import { compressFile } from "@/lib/server/attachment-compressor";
@@ -286,8 +287,8 @@ export async function uploadInvoiceToOrderItems(
   // `attachment-compressor.ts` for the URL-churn rationale.
   const { file: compressedTaggedFile } = await compressFile(taggedFile);
   for (const id of validIds) {
-    const form = new FormData();
-    form.append("order_item_attachements", compressedTaggedFile);
+    // Adds to the line — never replaces the driver's photo already there.
+    const form = addAttachmentForm(compressedTaggedFile, compressedTaggedFile.name);
     await pb.collection(collectionName).update(id, form);
   }
   return { filename: taggedFile.name, itemIds: validIds };
diff --git a/src/lib/server/collection-confirm-upload.test.ts b/src/lib/server/collection-confirm-upload.test.ts
index 996eb0e..224c857 100644
--- a/src/lib/server/collection-confirm-upload.test.ts
+++ b/src/lib/server/collection-confirm-upload.test.ts
@@ -94,7 +94,9 @@ describe("uploadInvoiceToOrderItems", () => {
     expect(update).toHaveBeenCalledTimes(2);
     const form = update.mock.calls[0]?.[1] as FormData;
     expect(form).toBeInstanceOf(FormData);
-    const uploaded = form.get("order_item_attachements") as File;
+    // "+" appends: the driver's photo already on the line must stay.
+    expect(form.get("order_item_attachements")).toBeNull();
+    const uploaded = form.get("order_item_attachements+") as File;
     expect(uploaded).toBeInstanceOf(File);
     expect(uploaded.name).toBe("[invoice] INV-1.pdf");
   });
diff --git a/src/lib/server/delivery-notes-service.ts b/src/lib/server/delivery-notes-service.ts
index ae60249..494772c 100644
--- a/src/lib/server/delivery-notes-service.ts
+++ b/src/lib/server/delivery-notes-service.ts
@@ -32,6 +32,7 @@
  *   - Other callers (cron, future bulk tools) can reuse these.
  */
 
+import { addAttachmentForm, attachmentList } from "@/lib/server/order-item-files";
 import { getAdminPocketBase } from "./pocketbase-admin";
 import { generateQuoteNumberServer } from "./quotes-service";
 import { renderDeliveryNotePdf } from "@/lib/pdf/render";
@@ -1410,8 +1411,7 @@ export async function createAdHocDeliveryNote(
     });
     await Promise.all(
       createdItems.map(async (it) => {
-        const form = new FormData();
-        form.append("order_item_attachements", blob, filename);
+        const form = addAttachmentForm(blob, filename, attachmentList((it as { order_item_attachements?: unknown }).order_item_attachements));
         await pb.collection(ORDER_ITEMS).update(it.id, form);
       }),
     );
@@ -1525,12 +1525,11 @@ export async function regenerateDeliveryNotePdf(
     logoDataUri,
   });
 
-  // Same upload pattern as `/api/invoicing/delivery-note` step 2:
-  // PB's file field PATCH REPLACES the existing list with whatever
-  // we send, so a re-regenerate cleanly overwrites the previous
-  // copy. Same filename → the retrieval endpoint (which looks for
-  // a file named `{deliveryNoteNumber}.pdf` on the first item)
-  // just picks up the new bytes.
+  // Same upload pattern as `/api/invoicing/delivery-note` step 2: add
+  // the new PDF and remove only this DN's older copies (a bare-field
+  // PATCH would wipe the driver's photo and supplier invoice too). The
+  // retrieval endpoint finds the file by its `{deliveryNoteNumber}.pdf`
+  // name.
   const filename = `${deliveryNoteNumber}.pdf`;
   // Compress the re-rendered PDF once outside the per-item loop.
   // A regenerate is the operator fixing a price/line error and
@@ -1548,8 +1547,9 @@ export async function regenerateDeliveryNotePdf(
   });
   await Promise.all(
     items.map(async (it) => {
-      const form = new FormData();
-      form.append("order_item_attachements", blob, filename);
+      // Replaces this DN's previous PDF only; the driver's photo and any
+      // supplier invoice on the line stay.
+      const form = addAttachmentForm(blob, filename, attachmentList((it as { order_item_attachements?: unknown }).order_item_attachements));
       await pb.collection(ORDER_ITEMS).update(it.id, form);
     }),
   );
diff --git a/src/lib/server/order-item-files.test.ts b/src/lib/server/order-item-files.test.ts
new file mode 100644
index 0000000..2ce7659
--- /dev/null
+++ b/src/lib/server/order-item-files.test.ts
@@ -0,0 +1,41 @@
+import { describe, expect, it } from "vitest";
+import { addAttachmentForm, isStoredCopyOf, pickStoredCopy } from "./order-item-files";
+
+describe("isStoredCopyOf", () => {
+  it("recognises PocketBase's stored name for an uploaded file", () => {
+    expect(isStoredCopyOf("dn26101913_ta9aoxfc9s.pdf", "DN26101913.pdf")).toBe(true);
+    expect(isStoredCopyOf("dn26101913_ta9aoxfc9s.pdf", "DN26101914.pdf")).toBe(false);
+    expect(isStoredCopyOf("dn261019131_ta9aoxfc9s.pdf", "DN26101913.pdf")).toBe(false);
+    expect(isStoredCopyOf("photo_ab12cd34ef.jpg", "DN26101913.pdf")).toBe(false);
+  });
+});
+
+describe("pickStoredCopy", () => {
+  it("finds the delivery-note PDF even when a driver photo comes first", () => {
+    expect(pickStoredCopy(["photo_ab12cd34ef.jpg", "dn26101913_ta9aoxfc9s.pdf"], "DN26101913.pdf")).toBe(
+      "dn26101913_ta9aoxfc9s.pdf",
+    );
+    expect(pickStoredCopy(["photo_ab12cd34ef.jpg"], "DN26101913.pdf")).toBeNull();
+  });
+});
+
+describe("addAttachmentForm", () => {
+  it("adds the file (never replaces) and drops older copies of the same document only", () => {
+    const blob = new Blob(["%PDF"], { type: "application/pdf" });
+    const form = addAttachmentForm(blob, "DN26101913.pdf", [
+      "driver_photo_ab12cd34ef.jpg",
+      "dn26101913_ta9aoxfc9s.pdf",
+      "invoice_inv_1_x1y2z3w4v5.pdf",
+    ]);
+    expect(form.get("order_item_attachements")).toBeNull();
+    const added = form.get("order_item_attachements+") as File;
+    expect(added.name).toBe("DN26101913.pdf");
+    expect(form.getAll("order_item_attachements-")).toEqual(["dn26101913_ta9aoxfc9s.pdf"]);
+  });
+
+  it("just adds when nothing older exists", () => {
+    const form = addAttachmentForm(new Blob(["x"]), "[invoice] INV-1.pdf");
+    expect((form.get("order_item_attachements+") as File).name).toBe("[invoice] INV-1.pdf");
+    expect(form.getAll("order_item_attachements-")).toEqual([]);
+  });
+});
diff --git a/src/lib/server/order-item-files.ts b/src/lib/server/order-item-files.ts
new file mode 100644
index 0000000..bc30950
--- /dev/null
+++ b/src/lib/server/order-item-files.ts
@@ -0,0 +1,56 @@
+/**
+ * Writing to `order_items.order_item_attachements`.
+ *
+ * The field holds everything on a line: the driver's photo, a supplier
+ * invoice the buyer uploaded, the delivery-note PDF. A PocketBase file
+ * PATCH under the bare field name REPLACES the list — on 2026-10-19 a
+ * buyer's "Add supplier invoice" silently deleted the driver's delivery
+ * note photo on PO202610008LIF, and generating a DN PDF did the same.
+ * Always add with `field+`; only a document's own older copies are
+ * removed (`field-`), e.g. when a DN PDF is regenerated.
+ */
+const FIELD = "order_item_attachements";
+
+/** PocketBase stores "DN26101913.pdf" as "dn26101913_<10 random>.pdf". */
+function storedStem(original: string): { stem: string; ext: string } {
+  const dot = original.lastIndexOf(".");
+  const base = dot > 0 ? original.slice(0, dot) : original;
+  const ext = dot > 0 ? original.slice(dot).toLowerCase() : "";
+  const stem = base
+    .replace(/([a-z0-9])([A-Z])/g, "$1_$2")
+    .toLowerCase()
+    .replace(/[^a-z0-9]+/g, "_")
+    .replace(/^_+|_+$/g, "");
+  return { stem, ext };
+}
+
+/** True when `stored` is PocketBase's saved name for an upload called `original`. */
+export function isStoredCopyOf(stored: string, original: string): boolean {
+  const { stem, ext } = storedStem(original);
+  if (!stem) return false;
+  const s = stored.toLowerCase();
+  return s.startsWith(`${stem}_`) && (!ext || s.endsWith(ext)) && /^[a-z0-9]{10}$/.test(s.slice(stem.length + 1, s.length - ext.length));
+}
+
+/** The stored copy of `original` among a line's files (newest wins), or null. */
+export function pickStoredCopy(files: string[], original: string): string | null {
+  const hits = files.filter((f) => isStoredCopyOf(f, original));
+  return hits.length > 0 ? hits[hits.length - 1] : null;
+}
+
+/**
+ * FormData that ADDS `file` to a line's attachments and removes only
+ * older stored copies of the same document from `existing`.
+ */
+export function addAttachmentForm(file: Blob, filename: string, existing: string[] = []): FormData {
+  const form = new FormData();
+  form.append(`${FIELD}+`, file, filename);
+  for (const old of existing.filter((f) => isStoredCopyOf(f, filename))) form.append(`${FIELD}-`, old);
+  return form;
+}
+
+/** A line's attachment list as an array (PB returns a string for single-file data). */
+export function attachmentList(raw: unknown): string[] {
+  if (Array.isArray(raw)) return raw.filter((f): f is string => typeof f === "string" && f !== "");
+  return typeof raw === "string" && raw ? [raw] : [];
+}