fix(stock-purchase-items): drop dead drv_collected_at write to unblock build

The markLineCollected service and the stock-orders page's
handleAssignDriver (delivery-sentinel auto-collect path) both
wrote `drv_collected_at` to `stock_purchase_items`, but that
field exists on `order_items`, not on `stock_purchase_items`
(verified against pb_schema-2.json). Per AGENTS.md "select
fields are not self-service", PB would 500 both writes at
runtime. The TS error from the service was the build break
flagged in the 2026-08-06 23:34 deployment.

The page.tsx write was a latent runtime bug — TypeScript
never caught it because PB's loose `update` patch typing
accepts any field name. Both writes are removed; the
collection moment is captured by PB's `updated` timestamp on
the line row, which is sufficient for the auto-collect audit
trail. Inline comments point to FEATURE-REQUESTS as the
follow-up if a dedicated collection-date field is wanted
later (would need a PB admin schema change).

Also drops the matching test assertions that read
`drv_collected_at` off the response and replaces them with
a comment explaining the absence.

Tests: vitest 59/59 across stock-purchase-items-service +
stock-orders/[id]; npm run build compiles clean
(Next.js 16.2.6 Turbopack + TypeScript).

Co-Authored-By: Claude <noreply@anthropic.com>

Co-authored-by: Orca <help@stably.ai>

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,

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

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 () => {

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