diff --git a/src/app/(app)/stock-orders/[id]/page.test.tsx b/src/app/(app)/stock-orders/[id]/page.test.tsx
index ce8c10d..c8d205e 100644
--- a/src/app/(app)/stock-orders/[id]/page.test.tsx
+++ b/src/app/(app)/stock-orders/[id]/page.test.tsx
@@ -264,7 +264,8 @@ describe("<StockOrderDetailPage /> — driver picker", () => {
       status: "collected",
       quantity_received: 5,
     });
-    expect(byId.get("si-1")?.drv_collected_at).toMatch(/^\d{4}-\d{2}-\d{2}T/);
+    // No `drv_collected_at` field on stock_purchase_items — collection
+    // moment is captured by PB's `updated` timestamp on the line row.
     expect(byId.get("si-2")).toMatchObject({
       status: "collected",
       quantity_received: 10,
diff --git a/src/app/(app)/stock-orders/[id]/page.tsx b/src/app/(app)/stock-orders/[id]/page.tsx
index 54834a8..91b3cb2 100644
--- a/src/app/(app)/stock-orders/[id]/page.tsx
+++ b/src/app/(app)/stock-orders/[id]/page.tsx
@@ -535,10 +535,16 @@ export default function StockOrderDetailPage({
           // The header is still "sent" until the operator clicks
           // "Confirm collection" — that final step is the audit
           // stamp that the warehouse-side has accepted the goods.
+          //
+          // NOTE: we deliberately do NOT write `drv_collected_at`
+          // here — that field exists on `order_items` but NOT on
+          // `stock_purchase_items` (PB schema gap; tracked in
+          // FEATURE-REQUESTS). PB would 500 the request. The
+          // collection timestamp is captured by PB's `updated` on
+          // the line row.
           await pb.collection("stock_purchase_items").update(line.id, {
             status: "collected",
             quantity_received: Number(line.quantity ?? 0),
-            drv_collected_at: now,
           });
         } else {
           // Real driver: just bind the line to the driver. The
diff --git a/src/lib/server/stock-purchase-items-service.test.ts b/src/lib/server/stock-purchase-items-service.test.ts
index 1aca73d..df032da 100644
--- a/src/lib/server/stock-purchase-items-service.test.ts
+++ b/src/lib/server/stock-purchase-items-service.test.ts
@@ -395,7 +395,9 @@ describe("markLineCollectedWithPb", () => {
     expect(result.item.quantity_received).toBe(10);
     expect(result.previous_quantity_received).toBe(0);
     expect(result.new_quantity_received).toBe(10);
-    expect(result.item.drv_collected_at).toMatch(/^\d{4}-\d{2}-\d{2}T/);
+    // The collection moment is captured by PB's `updated` timestamp
+    // on the line row (no dedicated `drv_collected_at` field on
+    // stock_purchase_items — see FEATURE-REQUESTS gap).
   });
 
   it("accepts the collection_pool auto-collect path", async () => {
diff --git a/src/lib/server/stock-purchase-items-service.ts b/src/lib/server/stock-purchase-items-service.ts
index db2831a..1b641ee 100644
--- a/src/lib/server/stock-purchase-items-service.ts
+++ b/src/lib/server/stock-purchase-items-service.ts
@@ -151,7 +151,13 @@ export async function updateStockPurchaseItemWithPb(
   const previous: Partial<StockPurchaseItem> = {};
   for (const key of STOCK_PURCHASE_ITEM_PATCHABLE_FIELDS) {
     if (key in input.patch) {
-      (previous as Record<string, unknown>)[key] = (before as Record<string, unknown>)[key];
+      // `StockPurchaseItem` has no string index signature, so the
+      // direct `as Record<string, unknown>` cast is rejected (TS2352).
+      // Detour through `unknown` — same pattern as the stock-items
+      // service.
+      (previous as unknown as Record<string, unknown>)[key] = (
+        before as unknown as Record<string, unknown>
+      )[key];
     }
   }
 
@@ -457,12 +463,16 @@ export async function markLineCollectedWithPb(
   }
 
   const new_quantity_received = previous_quantity_received + quantity_collected;
-  const now = new Date().toISOString();
 
+  // Note: `drv_collected_at` (the moment the driver handed the goods
+  // to the warehouse) does NOT exist on the `stock_purchase_items`
+  // PB collection — only `drv_id` + `assigned_at`. We track the
+  // collection moment via the line's `status` flip to `collected`
+  // and PB's `updated` timestamp. Adding a dedicated date field is
+  // a PB-admin task (FEATURE-REQUESTS gap #drv_collected_at_field).
   const patch: Record<string, unknown> = {
     status: "collected",
     quantity_received: new_quantity_received,
-    drv_collected_at: before.drv_collected_at ?? now,
   };
 
   const updated = (await pb