feat(buyer-tasks): surface email_error on buyer task groups

Adds an emailError field on BuyerTaskGroup so the UI can render
the send-pipeline failure reason. The value is truncated to 200
chars at the service boundary to keep the card layout bounded.

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

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

src/lib/server/buyer-tasks-service.test.ts

@@ -284,6 +284,34 @@ describe("listBuyerTasks", () => {
     expect(groups[0].supplierEmail).toBe("orders@steelco.example");
   });
 
+  it("populates emailError from the related PO when the PO has an email_error", async () => {
+    const { admin } = makeAdmin([
+      baseItem({
+        purchase_order: "po-1",
+        item_status: "po_generated",
+        expand: {
+          order: baseOrder,
+          supplier: baseSupplier,
+          purchase_order: {
+            id: "po-1",
+            status: "draft",
+            po_number: "PO-26080301",
+            email_error: "[webhook] Webhook returned HTTP 502",
+            expand: {
+              supplier: { id: "sup-1", email: "orders@steelco.example" },
+            },
+          },
+        },
+      }),
+    ]);
+    vi.mocked(getAdminPocketBase).mockResolvedValue(admin as never);
+
+    const groups = await listBuyerTasks("po_draft");
+
+    expect(groups).toHaveLength(1);
+    expect(groups[0].emailError).toBe("[webhook] Webhook returned HTTP 502");
+  });
+
   it("leaves poNumber and supplierEmail null when the PO has no expand", async () => {
     const { admin } = makeAdmin([
       baseItem({

src/lib/server/buyer-tasks-service.ts

@@ -27,6 +27,12 @@ export type BuyerTaskGroup = {
   poStatus: "draft" | "sent" | "sending" | "received" | "mail_failed" | "cancelled" | null;
   poNumber: string | null;
   supplierEmail: string | null;
+  /** Last send-pipeline error. Null on a clean draft or after a successful send.
+   *  Pulled from `purchase_orders.email_error` and truncated to 200 chars at
+   *  the service boundary so a runaway SMTP error doesn't blow up the card
+   *  layout. The full reason remains visible in the order page's send-modal
+   *  banner. */
+  emailError: string | null;
   step: BuyerTaskTab;
 };
 
@@ -103,6 +109,13 @@ export async function listBuyerTasks(tab: BuyerTaskTab): Promise<BuyerTaskGroup[
         poStatus: po?.status ?? null,
         poNumber: po && typeof po === "object" && "po_number" in po ? String((po as { po_number?: string }).po_number ?? "") || null : null,
         supplierEmail: (po as { expand?: { supplier?: { email?: string } } } | undefined)?.expand?.supplier?.email ?? null,
+        // Truncate the SMTP error to 200 chars at the service boundary so
+        // a runaway error string can't blow up the card layout. The full
+        // reason is still visible in the order page's send-modal banner.
+        emailError:
+          (po as { email_error?: string } | undefined)?.email_error
+            ? String((po as { email_error?: string }).email_error).slice(0, 200)
+            : null,
         step: tab,
       };
       groups.set(groupId, group);