diff --git a/src/app/(app)/collection-confirm/view-model.test.ts b/src/app/(app)/collection-confirm/view-model.test.ts
index d2c81a9..a6bbffb 100644
--- a/src/app/(app)/collection-confirm/view-model.test.ts
+++ b/src/app/(app)/collection-confirm/view-model.test.ts
@@ -3,6 +3,8 @@ import { describe, expect, it } from "vitest";
 import {
   appendConfirmingNote,
   appendNote,
+  appendCostNote,
+  dedupeAttachments,
   buildConfirmNote,
   buildConfirmPatch,
   buildReturnPatch,
@@ -363,4 +365,82 @@ describe("buildReturnPatch", () => {
       "Old",
     ]);
   });
+});
+
+describe("appendCostNote", () => {
+  it("writes a category=cost note with prev/new values and the actor", () => {
+    const result = JSON.parse(
+      appendCostNote("", { id: "u-1", name: "sj" }, 45, 50),
+    );
+    expect(result).toHaveLength(1);
+    expect(result[0]).toMatchObject({
+      actorId: "u-1",
+      actorName: "sj",
+      category: "cost",
+      body: { prevCost: 45, newCost: 50 },
+    });
+    expect(result[0].ts).toEqual(expect.any(String));
+  });
+
+  it("preserves existing notes when appending", () => {
+    const existing = JSON.stringify([
+      {
+        ts: "2026-07-01T00:00:00Z",
+        actorId: "u-1",
+        actorName: "sj",
+        category: "confirm",
+        body: "Confirmed for invoicing — INV-1",
+      },
+    ]);
+    const result = JSON.parse(appendCostNote(existing, { id: "u-2", name: "ab" }, 10, 12));
+    expect(result).toHaveLength(2);
+    expect(result[0].category).toBe("confirm");
+    expect(result[1].category).toBe("cost");
+  });
+
+  it("returns the original JSON when prevCost === newCost (no-op)", () => {
+    const existing = JSON.stringify([
+      {
+        ts: "2026-07-01T00:00:00Z",
+        actorId: "u-1",
+        actorName: "sj",
+        category: "note",
+        body: "hello",
+      },
+    ]);
+    expect(appendCostNote(existing, { id: "u-1", name: "sj" }, 10, 10)).toBe(existing);
+  });
+});
+
+describe("dedupeAttachments", () => {
+  it("returns one entry per distinct filename across rows", () => {
+    const rows = [
+      { order_item_attachements: ["INV-001.pdf", "DN-7.pdf"] },
+      { order_item_attachements: ["INV-002.pdf"] },
+    ];
+    const out = dedupeAttachments(rows);
+    expect(out).toEqual([
+      { filename: "INV-001.pdf", itemIds: [] },
+      { filename: "DN-7.pdf", itemIds: [] },
+      { filename: "INV-002.pdf", itemIds: [] },
+    ]);
+  });
+
+  it("groups duplicate filenames with the list of source item ids", () => {
+    const rows = [
+      { id: "a", order_item_attachements: ["INV-001.pdf"] },
+      { id: "b", order_item_attachements: ["INV-001.pdf", "DN-7.pdf"] },
+      { id: "c", order_item_attachements: ["DN-7.pdf"] },
+    ];
+    const out = dedupeAttachments(rows);
+    expect(out).toEqual([
+      { filename: "INV-001.pdf", itemIds: ["a", "b"] },
+      { filename: "DN-7.pdf", itemIds: ["b", "c"] },
+    ]);
+  });
+
+  it("returns an empty array when no rows have attachments", () => {
+    expect(dedupeAttachments([{ id: "a" }, { id: "b" }])).toEqual([]);
+    expect(dedupeAttachments([])).toEqual([]);
+  });
 });
\ No newline at end of file
diff --git a/src/app/(app)/collection-confirm/view-model.ts b/src/app/(app)/collection-confirm/view-model.ts
index a71972e..72092a9 100644
--- a/src/app/(app)/collection-confirm/view-model.ts
+++ b/src/app/(app)/collection-confirm/view-model.ts
@@ -1,4 +1,4 @@
-export type NoteCategory = "collection" | "note" | "problem" | "quantity" | "confirm";
+export type NoteCategory = "collection" | "note" | "problem" | "quantity" | "confirm" | "cost";
 
 export type NoteEntry = {
   ts: string;
@@ -58,7 +58,7 @@ export type PurchaseOrderGroup<T extends GroupableRow> = {
   rows: T[];
 };
 
-const NOTE_CATEGORIES: NoteCategory[] = ["collection", "note", "problem", "quantity", "confirm"];
+const NOTE_CATEGORIES: NoteCategory[] = ["collection", "note", "problem", "quantity", "confirm", "cost"];
 
 function isNoteEntry(value: unknown): value is NoteEntry {
   if (!value || typeof value !== "object") return false;
@@ -258,3 +258,39 @@ export function buildReturnPatch(input: ReturnPatchInput): ReturnPatch {
     notes,
   };
 }
+
+export function appendCostNote(
+  rawNotes: string | null | undefined,
+  actor: ConfirmActor,
+  prevCost: number,
+  newCost: number,
+): string {
+  if (prevCost === newCost) return rawNotes ?? "";
+  const existing = parseStoredNotes(rawNotes ?? "");
+  const entry = {
+    id: `cost-${Date.now()}-${Math.random().toString(36).slice(2, 8)}`,
+    ts: new Date().toISOString(),
+    actorId: actor.id,
+    actorName: actor.name,
+    category: "cost" as const,
+    body: { prevCost, newCost },
+  };
+  return JSON.stringify([...existing, entry]);
+}
+
+export type DedupedAttachment = { filename: string; itemIds: string[] };
+
+export function dedupeAttachments(
+  rows: Array<{ id?: string; order_item_attachements?: string[] | null }>,
+): DedupedAttachment[] {
+  const byFilename = new Map<string, string[]>();
+  for (const row of rows) {
+    const list = row.order_item_attachements ?? [];
+    for (const filename of list) {
+      const bucket = byFilename.get(filename) ?? [];
+      if (row.id) bucket.push(row.id);
+      byFilename.set(filename, bucket);
+    }
+  }
+  return Array.from(byFilename.entries()).map(([filename, itemIds]) => ({ filename, itemIds }));
+}