diff --git a/src/app/api/inbox-three/[batchId]/notes/[noteId]/lines/route.test.ts b/src/app/api/inbox-three/[batchId]/notes/[noteId]/lines/route.test.ts
new file mode 100644
index 0000000..9a05cad
--- /dev/null
+++ b/src/app/api/inbox-three/[batchId]/notes/[noteId]/lines/route.test.ts
@@ -0,0 +1,68 @@
+import { beforeEach, it, expect, vi } from "vitest";
+import { context } from "@/lib/dn-pipeline/preview-fixture";
+import { buildPreview } from "@/lib/dn-pipeline/ai-preview";
+import { decisionHash } from "@/lib/dn-pipeline/decision-hash";
+
+const m = vi.hoisted(() => ({ admin: vi.fn(), user: vi.fn(), site: vi.fn(), lease: vi.fn(), load: vi.fn(), batch: vi.fn() }));
+vi.mock("@/lib/pb", () => ({ pbAdmin: m.admin }));
+vi.mock("@/lib/auth/guard", () => ({ requireApiUser: m.user, requireSiteAccess: m.site }));
+vi.mock("@/lib/dn-pipeline/lock", () => ({ withBatchLease: m.lease }));
+vi.mock("@/lib/dn-pipeline/ai-preview-context", () => ({ loadPreviewContext: m.load }));
+
+import { POST } from "./route";
+
+const batch = "batchabcdefghij";
+const note = "noteabcdefghijk";
+const params = { params: Promise.resolve({ batchId: batch, noteId: note }) };
+const req = (body: object) => new Request("http://localhost", { method: "POST", body: JSON.stringify(body) });
+
+let c: ReturnType<typeof context>;
+let p: ReturnType<typeof buildPreview>;
+const edit = { lines: [0], poItemId: "itemabcdefghijk", slipQty: 11, slipUnit: "ea", factor: 1, price: null, usePoRate: true, reason: "11 pipes on the order." };
+const body = () => ({ edits: [edit], snapshotHash: p.snapshotHash, decisionHash: decisionHash(p) });
+
+beforeEach(() => {
+  vi.resetAllMocks();
+  c = context();
+  p = buildPreview(c, { allocations: [{ sourceLineIds: ["pipe"], purchaseOrderItemId: "itemabcdefghijk", quantityBasis: "direct", factor: 1, amountBasis: "po_rate", sourceAmountBasis: "unknown", ruleKeys: [], explanation: "Pipe", reviewQuestion: null }] });
+  m.load.mockResolvedValue({ context: c, stored: p });
+  m.user.mockResolvedValue({ id: "user", role: "office_user", modules: ["financial"] });
+  m.site.mockReturnValue(null);
+  m.admin.mockResolvedValue({ collection: (name: string) => ({ getOne: async () => (name === "dn_batches" ? { site: "site" } : { batch, supplier: "supplierabcdefg", purchase_order: "poabcdefghijklm" }) }) });
+  m.lease.mockImplementation(async (_p, _b, _w, fn) => ({ acquired: true, value: await fn({ batch: m.batch }) }));
+});
+
+it("keeps the site manager out of the office's screen", async () => {
+  m.user.mockResolvedValue({ id: "site", role: "site_user" });
+  expect((await POST(req(body()), params)).status).toBe(403);
+  expect(m.lease).not.toHaveBeenCalled();
+});
+
+it("saves the line edits and the audit without posting anything", async () => {
+  const res = await POST(req(body()), params);
+  expect(res.status).toBe(200);
+  const saved = await res.json();
+  expect(saved.rows[0]).toMatchObject({ numbers: [1], poItemId: "itemabcdefghijk" });
+  expect(saved.readyNow).toEqual([0]);
+  expect(m.batch.mock.calls[0][0].map((v: { collection: string }) => v.collection)).toEqual(["dn_batch_notes", "dn_review_events"]);
+  expect(m.batch.mock.calls[0][0][1]).toMatchObject({ collection: "dn_review_events", data: { action: "inbox_three_save", actor: "user" } });
+});
+
+it("refuses an edit made against a match that has moved on", async () => {
+  const old = decisionHash(p);
+  p.allocations[0].quantity = 99;
+  const res = await POST(req({ edits: [edit], snapshotHash: p.snapshotHash, decisionHash: old }), params);
+  expect(res.status).toBe(409);
+  expect(m.batch).not.toHaveBeenCalled();
+});
+
+it("writes nothing when one edit in the batch fails", async () => {
+  const res = await POST(req({ edits: [edit, { ...edit, poItemId: "foreignitem12345" }], snapshotHash: p.snapshotHash, decisionHash: decisionHash(p) }), params);
+  expect(res.status).toBe(409);
+  expect(m.batch).not.toHaveBeenCalled();
+});
+
+it("never reaches for the posting function", async () => {
+  const source = await import("node:fs/promises").then((fs) => fs.readFile(new URL("./route.ts", import.meta.url), "utf8"));
+  expect(source).not.toContain("postLineWithinLease");
+});
diff --git a/src/app/api/inbox-three/[batchId]/notes/[noteId]/lines/route.ts b/src/app/api/inbox-three/[batchId]/notes/[noteId]/lines/route.ts
new file mode 100644
index 0000000..891fed1
--- /dev/null
+++ b/src/app/api/inbox-three/[batchId]/notes/[noteId]/lines/route.ts
@@ -0,0 +1,84 @@
+import { NextResponse } from "next/server";
+import { pbAdmin } from "@/lib/pb";
+import { requireApiUser, requireSiteAccess } from "@/lib/auth/guard";
+import { canSeeInboxThree } from "@/lib/auth/access";
+import { withBatchLease } from "@/lib/dn-pipeline/lock";
+import { loadPreviewContext } from "@/lib/dn-pipeline/ai-preview-context";
+import { decisionHash } from "@/lib/dn-pipeline/decision-hash";
+import { buildLineRows } from "@/lib/inbox-three/line-rows";
+import { saveLineEdits } from "@/lib/inbox-three/save-lines";
+
+export const dynamic = "force-dynamic";
+export const runtime = "nodejs";
+
+/**
+ * Save the office's line edits.
+ *
+ * This route never posts a receipt. It writes the decisions the clerk made
+ * and moves the note to Ready to post when a line has nothing left to ask.
+ */
+export async function POST(
+  request: Request,
+  { params }: { params: Promise<{ batchId: string; noteId: string }> },
+) {
+  const user = await requireApiUser("financial");
+  if (user instanceof Response) return user;
+  // Inbox 3 is the office's screen while it is being tested.
+  if (!canSeeInboxThree(user)) return NextResponse.json({ error: "not_allowed" }, { status: 403 });
+  const { batchId, noteId } = await params;
+  if (![batchId, noteId].every((value) => /^[a-z0-9]{15}$/i.test(value)))
+    return NextResponse.json({ error: "invalid_id" }, { status: 400 });
+  const body = await request.json().catch(() => null);
+  const edits = body && typeof body === "object" && Array.isArray((body as { edits?: unknown }).edits) ? (body as { edits: unknown[] }).edits : null;
+  if (!edits) return NextResponse.json({ error: "invalid_body" }, { status: 400 });
+
+  const pb = await pbAdmin();
+  const [batch, note] = await Promise.all([
+    pb.collection("dn_batches").getOne(batchId).catch(() => null),
+    pb.collection("dn_batch_notes").getOne(noteId).catch(() => null),
+  ]);
+  if (!batch || !note || note.batch !== batchId) return NextResponse.json({ error: "not_found" }, { status: 404 });
+  const denied = requireSiteAccess(user, String(batch.site ?? ""));
+  if (denied) return denied;
+
+  try {
+    const result = await withBatchLease(pb, batchId, "inbox-three-lines", async (lease) => {
+      const { context, stored } = await loadPreviewContext(pb, batchId, noteId);
+      if (!stored) throw Error("There is no saved match to edit. Run matching again.");
+      // The clerk edited what is on screen. If the match moved under them,
+      // their edit is against a different thing.
+      if (body.snapshotHash !== stored.snapshotHash || body.decisionHash !== decisionHash(stored))
+        throw Error("Matching result changed; refresh before continuing");
+      // Every edit is applied to a copy: a batch that fails halfway leaves
+      // the saved match exactly as it was.
+      const { preview, remembered, readyNow } = saveLineEdits(context, stored, edits as never, user.id);
+      await lease.batch([
+        ...(remembered
+          ? [{ collection: "suppliers", method: "update" as const, id: String(context.supplier.id), data: { reconciliation_rules: remembered } }]
+          : []),
+        { collection: "dn_batch_notes", method: "update", id: noteId, data: {
+          reconciliation_preview: preview,
+          status: readyNow.length ? "candidate" : "blocked",
+          stage: readyNow.length ? "ready_to_post" : "needs_review",
+        } },
+        { collection: "dn_review_events", method: "create", data: {
+          batch: batchId,
+          note: noteId,
+          actor: user.id,
+          action: "inbox_three_save",
+          reason: "Saved Inbox 3 line edits; no receipt posted.",
+          after: { edits },
+        } },
+      ]);
+      return { rows: buildLineRows(context, preview), readyNow };
+    });
+    return result.acquired
+      ? NextResponse.json(result.value)
+      : NextResponse.json({ error: "locked", detail: "This delivery is being updated. Try again shortly." }, { status: 409 });
+  } catch (error) {
+    return NextResponse.json(
+      { error: "lines_not_saved", detail: `${error instanceof Error ? error.message : "Unable to save the line edits"}. Nothing was changed.` },
+      { status: 409 },
+    );
+  }
+}
diff --git a/src/lib/inbox-three/save-lines.test.ts b/src/lib/inbox-three/save-lines.test.ts
new file mode 100644
index 0000000..a37c988
--- /dev/null
+++ b/src/lib/inbox-three/save-lines.test.ts
@@ -0,0 +1,103 @@
+import { describe, expect, it } from "vitest";
+import { buildPreview, type PreviewContext } from "@/lib/dn-pipeline/ai-preview";
+import { saveLineEdits } from "./save-lines";
+import type { LineEdit } from "./line-rows";
+
+const MESH_ITEM = "meshitem1234567";
+const BAILING_ITEM = "bailingitem12345";
+/** An order line from another purchase order. */
+const FOREIGN_ITEM = "foreignitem12345";
+
+const context = (): PreviewContext => ({
+  note: { id: "noteabcdefghijk", batch: "batchabcdefghij", pages: [1], doc_number: "0007075669", items: [] },
+  pages: [],
+  supplier: { id: "supplierabcdefg", name: "Vula" },
+  po: { id: "poabcdefghijklm", purchase_order_number: "MEGCPO9448", total_value: 11748.7 },
+  poItems: [
+    { id: MESH_ITEM, description: "MESH DIAMOND 600 x 2.5 ROLL", unit: "m", qty: 2, rate: 1124.35, disc_percent: 0, vat_percent: 15 },
+    { id: BAILING_ITEM, description: "1.6mm Bailing Wire", unit: "ea", qty: 100, rate: 95, disc_percent: 0, vat_percent: 15 },
+  ],
+  lines: [
+    { sourceLineId: "mesh", description: "MESH DIAMOND … ROLL", qty: 2, unit: "roll", unit_price: 1298, line_amount: 2596, product_code: null },
+    { sourceLineId: "kerb-a", description: "KERB 150", qty: 4, unit: "ea", unit_price: 95, line_amount: 380, product_code: null },
+    { sourceLineId: "kerb-b", description: "KERB 150", qty: 4, unit: "ea", unit_price: 95, line_amount: 380, product_code: null },
+    { sourceLineId: "kerb-c", description: "KERB 150", qty: 4, unit: "ea", unit_price: 95, line_amount: 380, product_code: null },
+    { sourceLineId: "bailing", description: "1.6mm Bailing Wire", qty: 25, unit: "ea", unit_price: 95, line_amount: 2375, product_code: null },
+  ],
+  priorDeliveries: [],
+  priorItems: [],
+});
+
+const preview = (c: PreviewContext) => buildPreview(c, { allocations: [
+  { sourceLineIds: ["mesh"], purchaseOrderItemId: MESH_ITEM, quantityBasis: "direct", factor: 1, amountBasis: "po_rate", sourceAmountBasis: "unknown", ruleKeys: [], explanation: "Mesh diamond roll", reviewQuestion: null },
+  { sourceLineIds: ["kerb-a"], purchaseOrderItemId: null, quantityBasis: "none", factor: null, amountBasis: "unknown", sourceAmountBasis: "unknown", ruleKeys: [], explanation: "Kerb", reviewQuestion: null },
+  { sourceLineIds: ["kerb-b"], purchaseOrderItemId: null, quantityBasis: "none", factor: null, amountBasis: "unknown", sourceAmountBasis: "unknown", ruleKeys: [], explanation: "Kerb", reviewQuestion: null },
+  { sourceLineIds: ["kerb-c"], purchaseOrderItemId: null, quantityBasis: "none", factor: null, amountBasis: "unknown", sourceAmountBasis: "unknown", ruleKeys: [], explanation: "Kerb", reviewQuestion: null },
+  { sourceLineIds: ["bailing"], purchaseOrderItemId: null, quantityBasis: "none", factor: null, amountBasis: "unknown", sourceAmountBasis: "unknown", ruleKeys: [], explanation: "Bailing wire", reviewQuestion: null },
+] });
+
+const edit = (over: Partial<LineEdit> = {}): LineEdit => ({
+  lines: [4],
+  poItemId: BAILING_ITEM,
+  slipQty: 25,
+  slipUnit: "ea",
+  factor: 1,
+  price: null,
+  usePoRate: true,
+  reason: "This is the bailing wire on the order.",
+  ...over,
+});
+
+describe("saveLineEdits", () => {
+  it("fixes a line onto the right order line and readies it", () => {
+    const c = context();
+    const result = saveLineEdits(c, preview(c), [edit()], "operator");
+    expect(result.readyNow).toEqual([4]);
+    expect(result.preview.allocations[4]).toMatchObject({ purchaseOrderItemId: BAILING_ITEM, status: "proposed" });
+  });
+
+  it("refuses an order line from another purchase order and changes nothing", () => {
+    const c = context();
+    const before = preview(c);
+    const untouched = structuredClone(before);
+    expect(() => saveLineEdits(c, before, [edit({ poItemId: FOREIGN_ITEM })], "operator")).toThrow(/PO item does not belong to this purchase order/);
+    expect(before).toEqual(untouched);
+  });
+
+  it("refuses to combine lines that are already posted", () => {
+    const c = context();
+    const p = preview(c);
+    p.allocations[3].posted = true;
+    expect(() => saveLineEdits(c, p, [edit({ lines: [2, 3], poItemId: BAILING_ITEM })], "operator")).toThrow(/Line 4 is already posted/);
+  });
+
+  it("remembers the receiving connection behind a roll to metre factor", () => {
+    const c = context();
+    const result = saveLineEdits(c, preview(c), [edit({
+      lines: [0],
+      poItemId: MESH_ITEM,
+      slipQty: 2,
+      slipUnit: "roll",
+      factor: 30,
+      reason: "One roll is 30 m.",
+    })], "operator");
+    const rules = (result.remembered as { rules?: { receiving_match?: { factor?: number } }[] } | null)?.rules ?? [];
+    expect(rules.some((rule) => rule.receiving_match?.factor === 30)).toBe(true);
+  });
+
+  it("saves nothing when one edit in the batch fails", () => {
+    const c = context();
+    const before = preview(c);
+    const untouched = structuredClone(before);
+    expect(() => saveLineEdits(c, before, [
+      edit(),
+      edit({ lines: [0], poItemId: FOREIGN_ITEM }),
+    ], "operator")).toThrow(/PO item does not belong to this purchase order/);
+    expect(before).toEqual(untouched);
+  });
+
+  it("never reaches for the posting function", async () => {
+    const source = await import("node:fs/promises").then((fs) => fs.readFile(new URL("./save-lines.ts", import.meta.url), "utf8"));
+    expect(source).not.toContain("postLineWithinLease");
+  });
+});
diff --git a/src/lib/inbox-three/save-lines.ts b/src/lib/inbox-three/save-lines.ts
new file mode 100644
index 0000000..643fedd
--- /dev/null
+++ b/src/lib/inbox-three/save-lines.ts
@@ -0,0 +1,117 @@
+/**
+ * Saving the office's line edits.
+ *
+ * The clerk edits a row — the order line, the factor, the price — and this
+ * turns those edits into the decisions the preview holds. It never posts a
+ * receipt: the office still presses Confirm, and the stage only says
+ * "ready to post" when a line has nothing left to ask.
+ *
+ * Every edit is applied to a copy, so a batch of edits that fails halfway
+ * leaves the saved match exactly as it was.
+ */
+import { buildPreview, snapshotHash, type PreviewContext, type ProcessingPreview } from "@/lib/dn-pipeline/ai-preview";
+import { resolveMatch } from "@/lib/dn-pipeline/matching";
+import { rememberConnection } from "@/lib/dn-pipeline/remembered-match";
+import { stableSourceKey } from "@/lib/dn-pipeline/line-booking";
+import { readyIndexes } from "@/lib/inbox-three/readiness";
+import { buildLineRows, editToConfirmation, type LineEdit } from "./line-rows";
+
+const sameLines = (a: readonly string[], b: readonly string[]) =>
+  a.length === b.length && [...a].sort().join("|") === [...b].sort().join("|");
+
+/** Has this slip line already been booked? */
+function isPosted(context: PreviewContext, preview: ProcessingPreview, sourceLineId: string): boolean {
+  if (preview.allocations.some((allocation) => allocation.posted && allocation.sourceLineIds.includes(sourceLineId))) return true;
+  const state = context.note.line_posting as { bookings?: { sourceKeys?: string[] }[] } | undefined;
+  const key = stableSourceKey(sourceLineId);
+  return (state?.bookings ?? []).some((booking) => (booking.sourceKeys ?? []).includes(key));
+}
+
+/**
+ * Apply the office's edits to the saved match.
+ *
+ * `edits` carry 0-based line numbers. The result is a new preview, the
+ * supplier guidance a remembered connection produced (if any), and the
+ * lines that are ready to confirm now.
+ */
+export function saveLineEdits(
+  context: PreviewContext,
+  preview: ProcessingPreview,
+  edits: LineEdit[],
+  actor: string,
+): { preview: ProcessingPreview; remembered: Record<string, unknown> | null; readyNow: number[] } {
+  let working = context;
+  let current = preview;
+  let remembered: Record<string, unknown> | null = null;
+
+  for (const edit of edits) {
+    if (!edit.lines.length) throw Error("Choose the line this edit is for.");
+    const indexes = [...edit.lines].sort((a, b) => a - b);
+    for (const index of indexes) {
+      if (!Number.isInteger(index) || index < 0 || index >= working.lines.length) throw Error("A line is not on this delivery.");
+    }
+    const sourceLineIds = indexes.map((index) => working.lines[index].sourceLineId);
+
+    // A posted line is evidence. It cannot be edited.
+    const posted = indexes.find((index) => isPosted(working, current, working.lines[index].sourceLineId));
+    if (posted !== undefined) throw Error(`Line ${posted + 1} is already posted`);
+
+    // The order line has to belong to this order.
+    if (edit.poItemId && !working.poItems.some((item) => item.id === edit.poItemId)) {
+      throw Error("PO item does not belong to this purchase order");
+    }
+
+    // The allocation this edit belongs to: the one covering exactly these
+    // lines, or a rebuild when the clerk combined lines that were apart.
+    let next = current;
+    let index = next.allocations.findIndex((allocation) => sameLines(allocation.sourceLineIds, sourceLineIds));
+    if (index < 0) {
+      const untouched = next.allocations.filter((allocation) => !allocation.sourceLineIds.some((id) => sourceLineIds.includes(id)));
+      const factor = edit.factor ?? 1;
+      next = buildPreview(working, { allocations: [...untouched, {
+        sourceLineIds,
+        purchaseOrderItemId: edit.poItemId,
+        quantityBasis: sourceLineIds.length > 1 ? "kit" : factor === 1 ? "direct" : "converted",
+        factor: factor === 1 ? null : factor,
+        amountBasis: "po_rate",
+        sourceAmountBasis: "unknown",
+        ruleKeys: [],
+        explanation: `Combined by the office: ${sourceLineIds.length} slip lines`,
+        reviewQuestion: null,
+      }] });
+      index = next.allocations.findIndex((allocation) => sameLines(allocation.sourceLineIds, sourceLineIds));
+      if (index < 0) throw Error("The edited lines could not be matched to the purchase order.");
+    }
+
+    const row = buildLineRows(working, next)[index];
+    const confirmation = editToConfirmation(row, edit, edit.poItemId ? row.poUnit : null);
+
+    try {
+      current = resolveMatch(working, next, { index, sourceLineIds, snapshotHash: next.snapshotHash, confirmation });
+    } catch (error) {
+      // The clerk confirmed a quantity that is over what the order has left.
+      // Their reason is the acknowledgement; without it the line stays open.
+      if (!(error instanceof Error) || !/Acknowledge the cumulative excess/.test(error.message)) throw error;
+      current = resolveMatch(working, next, { index, sourceLineIds, snapshotHash: next.snapshotHash, confirmation: { ...confirmation, acceptExcess: true } });
+    }
+
+    // A remembered receiving connection is the supplier's rule, not the
+    // receipt's: it is kept so the next slip of the same goods converts
+    // itself. It only makes sense for a real unit conversion.
+    const item = edit.poItemId ? working.poItems.find((candidate) => candidate.id === edit.poItemId) : null;
+    const targetUnit = item && typeof item.unit === "string" ? item.unit : null;
+    if (targetUnit && edit.factor !== null && edit.factor !== 1 && edit.slipUnit.trim().toLowerCase() !== targetUnit.trim().toLowerCase()) {
+      const guidance = rememberConnection(
+        { ...working, supplier: { ...working.supplier, reconciliation_rules: remembered ?? working.supplier.reconciliation_rules } },
+        current,
+        current.allocations.findIndex((allocation) => sameLines(allocation.sourceLineIds, sourceLineIds)),
+        actor,
+      );
+      remembered = guidance;
+      working = { ...working, supplier: { ...working.supplier, reconciliation_rules: guidance } };
+      current = { ...current, snapshotHash: snapshotHash(working) };
+    }
+  }
+
+  return { preview: current, remembered, readyNow: readyIndexes(working, current) };
+}