fix(GRO-2234): transparent re-mint on 401 for portal Book New submit

A deliberately-paced Book New wizard could outlive the portal impersonation
session, so the final POST /api/portal/waitlist returned 401 and the UI showed
"Failed to book appointment. Please try again."

BookingFlow now retries once on a 401: it re-mints a fresh portal session via
POST /api/portal/session-from-auth (the customer's Better Auth cookie is still
valid) and resubmits the waitlist request with the new
X-Impersonation-Session-Id. Falls through to the existing error if no Better
Auth session is available (staff/dev impersonation paths).

- Appointments.tsx: remintPortalSession() helper; handleConfirmBooking submits
  via submitWaitlist(id) and retries once after a 401 re-mint.
- Test: first waitlist POST 401 -> re-mint -> retry with fresh id -> success;
  asserts exactly one re-mint and the header sequence.
- UAT_PLAYBOOK.md 5.12e: TC-WEB-5.12.25 slow-wizard submit succeeds.

Companion to groombook/api GRO-2234 (bounded sliding expiration).

Co-Authored-By: Paperclip <noreply@paperclip.ing>

src/__tests__/Appointments.test.tsx

@@ -801,4 +801,75 @@ describe("BookingFlow Book New funnel (GRO-2213)", () => {
     expect(body.preferredTime).toBe("10:00:00");
     expect(body.preferredDate).toBe("2026-06-09");
   });
+
+  it("re-mints the portal session and retries once when waitlist returns 401 (GRO-2234)", async () => {
+    const calls = { waitlist: 0, remint: 0 };
+    const waitlistHeaders: string[] = [];
+    const routed = (input: RequestInfo | URL, init?: RequestInit) => {
+      const url = typeof input === "string" ? input : input.toString();
+      if (url.includes("/api/portal/pets")) {
+        return Promise.resolve({
+          ok: true,
+          json: async () => ({ pets: [{ id: "pet-1", name: "Buddy", breed: "Lab" }] }),
+        } as Response);
+      }
+      if (url.includes("/api/portal/services")) {
+        return Promise.resolve({
+          ok: true,
+          json: async () => ({
+            services: [{ id: "service-1", name: "Bath & Brush", isAddOn: false, duration: 60, price: 50 }],
+          }),
+        } as Response);
+      }
+      if (url.includes("/api/book/availability")) {
+        return Promise.resolve({
+          ok: true,
+          json: async () => ["2026-06-09T10:00:00.000Z"],
+        } as Response);
+      }
+      if (url.includes("/api/portal/session-from-auth")) {
+        calls.remint += 1;
+        return Promise.resolve({
+          ok: true,
+          json: async () => ({ sessionId: "fresh-session-id", clientId: "c1", clientName: "Jane" }),
+        } as Response);
+      }
+      if (url.includes("/api/portal/waitlist")) {
+        calls.waitlist += 1;
+        const headers = (init?.headers ?? {}) as Record<string, string>;
+        waitlistHeaders.push(headers["X-Impersonation-Session-Id"] ?? "");
+        // First attempt: session lapsed → 401. Retry after re-mint: success.
+        if (calls.waitlist === 1) {
+          return Promise.resolve({ ok: false, status: 401, json: async () => ({ error: "Unauthorized" }) } as Response);
+        }
+        return Promise.resolve({ ok: true, status: 201, json: async () => ({}) } as Response);
+      }
+      return Promise.resolve({ ok: true, json: async () => ({}) } as Response);
+    };
+    global.fetch = vi.fn().mockImplementation(routed as typeof fetch);
+
+    render(<BookingFlow onClose={() => {}} sessionId="stale-session-id" />);
+
+    await waitFor(() => expect(screen.getByText("Buddy")).toBeInTheDocument());
+    fireEvent.click(screen.getByText("Buddy"));
+    await waitFor(() => expect(screen.getByText("Bath & Brush")).toBeInTheDocument());
+    fireEvent.click(screen.getByText("Bath & Brush"));
+    fireEvent.click(screen.getByRole("button", { name: /^Next$/ }));
+    await waitFor(() => expect(screen.getByText("First Available")).toBeInTheDocument());
+    fireEvent.click(screen.getByRole("button", { name: /^Next$/ }));
+    await waitFor(() => expect(screen.getByLabelText(/date/i)).toBeInTheDocument());
+    fireEvent.change(screen.getByLabelText(/date/i), { target: { value: "2026-06-09" } });
+    await waitFor(() => expect(screen.getByText("10:00 AM")).toBeInTheDocument());
+    fireEvent.click(screen.getByText("10:00 AM"));
+    fireEvent.click(screen.getByRole("button", { name: /^Next$/ }));
+    await waitFor(() => expect(screen.getByText(/Review & Confirm/i)).toBeInTheDocument());
+    fireEvent.click(screen.getByRole("button", { name: /Confirm Booking/i }));
+
+    // Re-mint happened exactly once, waitlist retried with the fresh id, and the
+    // booking succeeded (no error surfaced).
+    await waitFor(() => expect(calls.waitlist).toBe(2));
+    expect(calls.remint).toBe(1);
+    expect(waitlistHeaders).toEqual(["stale-session-id", "fresh-session-id"]);
+    expect(screen.queryByText(/Failed to book appointment/i)).not.toBeInTheDocument();
+  });
 });