test(giellie): pin the negative-quantity safety cases

The ledger asked the final review to close this gap, and it was still
open: the negative-quantity test asserted the ledger row (the delta and
the note) but never the persisted `stock_items` patch, and nothing pinned
a negative `targetQty` under `allowNegativeQty` — where the code applies
the negative allowance only to `currentQty`.

- The negative-quantity test now also asserts the persisted patch
  carries `current_qty: -3`.
- A new test asserts a negative `targetQty` is still rejected while
  `allowNegativeQty` is set, and that nothing is written.

src/lib/server/stock-quantities-service.test.ts

@@ -15,6 +15,7 @@ function stubPb(args: {
   updated?: Record<string, unknown>;
 }) {
   const ledgerCreates: Array<Record<string, unknown>> = [];
+  const stockUpdates: Array<Record<string, unknown>> = [];
   const updated = args.updated ?? { ...args.before };
   return {
     pb: {
@@ -22,7 +23,12 @@ function stubPb(args: {
         if (name === "stock_items") {
           return {
             getOne: vi.fn().mockResolvedValue(args.before),
-            update: vi.fn().mockResolvedValue(updated),
+            update: vi.fn().mockImplementation(
+              async (_id: string, patch: Record<string, unknown>) => {
+                stockUpdates.push(patch);
+                return updated;
+              },
+            ),
             create: vi.fn(),
           };
         }
@@ -38,6 +44,7 @@ function stubPb(args: {
       },
     },
     ledgerCreates,
+    stockUpdates,
   } as const;
 }
 
@@ -454,7 +461,7 @@ describe("updateStockItemsQuantities — negative quantities", () => {
   });
 
   it("accepts a negative currentQty when allowNegativeQty is set", async () => {
-    const { pb, ledgerCreates } = stubPb({
+    const { pb, ledgerCreates, stockUpdates } = stubPb({
       before: { id: "abcdefghijklmno", current_qty: 5 },
     });
     const res = await updateStockItemsQuantities({
@@ -466,6 +473,24 @@ describe("updateStockItemsQuantities — negative quantities", () => {
     expect(res.summary.succeeded).toBe(1);
     expect(ledgerCreates[0].change_qty).toBe(-8);
     expect(ledgerCreates[0].notes).toBe("Dave edited qty 5 → -3 via Giellie");
+    // The negative quantity is persisted, not just recorded.
+    expect(stockUpdates[0]).toMatchObject({ current_qty: -3 });
+  });
+
+  it("rejects a negative targetQty even when allowNegativeQty is set", async () => {
+    const { pb, stockUpdates } = stubPb({
+      before: { id: "abcdefghijklmno", current_qty: 5 },
+    });
+    const res = await updateStockItemsQuantities({
+      pb: pb as never,
+      updates: [{ id: "abcdefghijklmno", targetQty: -1 }],
+      actor: { id: "u1", name: "Dave" },
+      allowNegativeQty: true,
+    } as UpdateStockItemsQuantitiesInput);
+    const row = res.results[0];
+    expect(row.ok).toBe(false);
+    expect(row.ok === false && row.reason).toBe("validation_error");
+    expect(stockUpdates).toHaveLength(0);
   });
 
   it("keeps minQty floored at zero even with allowNegativeQty", async () => {