feat(collection-confirm): improve idempotency handling in stock confirmation

- Updated the `confirmStockRows` function to handle cases where a stock line is already fully received, returning a success response without throwing an error. This change prevents the confirm-stock button from becoming inoperable due to previous confirmations.
- Enhanced tests to verify the new behavior, ensuring that full-quantity rows are omitted from updates and partial rows are processed correctly.
- Added documentation to clarify the idempotency behavior and its implications for the stock confirmation process.

src/lib/server/collection-confirm-service.test.ts

@@ -940,7 +940,13 @@ describe("confirmStockRows", () => {
     expect(lineUpdate).not.toHaveBeenCalled();
   });
 
-  it("throws and skips the row when quantity is already fully received", async () => {
+  it("is idempotent: a line already at full quantity_received is omitted from updatedIds (no throw)", async () => {
+    // Old behaviour threw a plain Error here → 500. Once the qty
+    // pencil landed, snapping quantity_received to the full qty
+    // could leave the line "stuck" — the confirm-stock button
+    // would 500 forever. Now it's a no-op success: the row is
+    // dropped from updatedIds so the route returns 200 with the
+    // remaining rows only.
     const line = {
       id: "spi-1",
       stock_item: "st-1",
@@ -953,13 +959,45 @@ describe("confirmStockRows", () => {
     });
     vi.mocked(getAdminPocketBase).mockResolvedValue(admin as never);
 
-    await expect(
-      confirmStockRows(["spi-1"], { actor: { id: "u-1", name: "sj" } }),
-    ).rejects.toThrow(/already fully confirmed/i);
+    const result = await confirmStockRows(["spi-1"], {
+      actor: { id: "u-1", name: "sj" },
+    });
 
+    expect(result).toEqual([]);
     expect(lineUpdate).not.toHaveBeenCalled();
   });
 
+  it("processes a mixed batch: full-qty rows are skipped, partial rows are advanced", async () => {
+    const lines = {
+      "spi-1": {
+        id: "spi-1",
+        stock_item: "st-1",
+        quantity: 10,
+        quantity_received: 10, // already full
+        purchase: "sp-1",
+      },
+      "spi-2": {
+        id: "spi-2",
+        stock_item: "st-2",
+        quantity: 4,
+        quantity_received: 2, // partial
+        purchase: "sp-1",
+      },
+    };
+    const { admin, lineUpdate } = makeConfirmAdmin({
+      lineById: lines,
+    });
+    vi.mocked(getAdminPocketBase).mockResolvedValue(admin as never);
+
+    const result = await confirmStockRows(["spi-1", "spi-2"], {
+      actor: { id: "u-1", name: "sj" },
+    });
+
+    expect(result).toEqual(["spi-2"]);
+    expect(lineUpdate).toHaveBeenCalledTimes(1);
+    expect(lineUpdate).toHaveBeenCalledWith("spi-2", { quantity_received: 4 });
+  });
+
   it("throws and skips the row when the parent purchase id is missing", async () => {
     const line = {
       id: "spi-1",

src/lib/server/collection-confirm-service.ts

@@ -744,6 +744,20 @@ export async function confirmStockRows(
  *
  * `pb` is the admin PocketBase client; the function reads / updates
  * the relevant collections directly.
+ *
+ * ## Idempotency
+ *
+ * If the line is already fully received (`quantity_received >=
+ * quantity`), `confirmStockRowForId` returns `false` so the caller
+ * drops it from the `updatedIds` list. The route surfaces this as a
+ * 200 with the row omitted from `updatedIds` — the warehouse-side
+ * "Confirm collection" button is the operator's explicit close-of-
+ * day action; a previous confirm (or the qty pencil that snapped
+ * `quantity_received` up to the full qty) means there's nothing
+ * left to advance. The previous behaviour threw a plain Error →
+ * 500, which was a foot-gun once the qty pencil arrived: setting
+ * the qty to the full value would leave the confirm-stock button
+ * inoperable for that card.
  */
 async function confirmStockRowForId(
   pb: Awaited<ReturnType<typeof getAdminPocketBase>>,
@@ -767,7 +781,11 @@ async function confirmStockRowForId(
   }
   const alreadyReceived = Number(line.quantity_received ?? 0);
   if (alreadyReceived >= qty) {
-    throw new Error(`Stock line ${id} is already fully confirmed.`);
+    // Idempotent no-op: the line is already at full received. The
+    // qty pencil is one way to land here (operator snapped the qty
+    // up to the full qty before clicking confirm); a previous
+    // confirm-stock is another. Either way there's nothing to do.
+    return false;
   }
   if (!line.purchase) {
     throw new Error(