fix(billing): preserve entitlements and bound cancellation cleanup

Integrate the latest cancellation-reason flow from master. Keep paid periods and independent trials intact, stop collection without erasing historical or mixed receivables, and make scheduled and partial cancellations recoverable. Add regression coverage for invoice boundaries, entitlement expiry, cancellation selection and concurrent reason writes.

tests/component/settings-billing.test.tsx

@@ -1,5 +1,6 @@
 import { afterEach, describe, expect, it, vi } from 'vitest';
-import { render, screen } from '@testing-library/react';
+import { render, screen, within } from '@testing-library/react';
+import userEvent from '@testing-library/user-event';
 import SettingsPage from '@/app/(dashboard)/settings/settings-page-client';
 
 function renderScheduledCancellation(status: 'ACTIVE' | 'TRIALING') {
@@ -70,3 +71,86 @@ describe('scheduled cancellation in billing settings', () => {
     );
   });
 });
+
+function renderPastDue(hasBillingAccess: boolean) {
+  vi.stubGlobal(
+    'fetch',
+    vi.fn(async (url: string) => {
+      if (url !== '/api/billing') return { ok: false };
+      return {
+        ok: true,
+        json: async () => ({
+          data: {
+            isEnabled: true,
+            isConfigured: true,
+            checkoutAvailable: false,
+            portalAvailable: true,
+            cancelAvailable: true,
+            cancelIsImmediate: true,
+            needsPaymentFix: true,
+            openInvoice: null,
+            workspaceCreation: { canCreateWorkspace: hasBillingAccess, canStartTrial: false },
+            subscription: {
+              status: 'PAST_DUE',
+              label: 'Past due',
+              hasActiveSubscription: false,
+              hasRecoverableSubscription: true,
+              hasActiveTrial: false,
+              hasBillingAccess,
+              currentPeriodEnd: '2026-10-08T12:00:00Z',
+              trialEndsAt: null,
+              cancelAtPeriodEnd: false,
+              cancelAt: null,
+            },
+          },
+        }),
+      };
+    })
+  );
+  render(<SettingsPage billingOnly />);
+}
+
+describe('past-due access in billing settings', () => {
+  it('opens immediate unpaid cancellation copy and waits for confirmation', async () => {
+    const user = userEvent.setup();
+    renderPastDue(true);
+
+    await user.click(await screen.findByRole('button', { name: 'Cancel subscription' }));
+
+    const dialog = within(screen.getByRole('dialog'));
+    expect(dialog.getByText(/This subscription ends immediately\./)).toHaveTextContent(
+      'Canceling does not extend access to your workspaces.'
+    );
+    expect(dialog.getByText(/Automatic collection stops/)).toHaveTextContent(
+      'charges for prior service and other items may still be owed.'
+    );
+    expect(dialog.queryByText(/Everything stays on until/)).not.toBeInTheDocument();
+    expect(dialog.getByRole('button', { name: 'Cancel subscription' })).toBeEnabled();
+    expect(vi.mocked(fetch).mock.calls.some(([url]) => url === '/api/billing/cancel')).toBe(false);
+
+    await user.click(dialog.getByRole('button', { name: 'Keep subscription' }));
+
+    expect(screen.queryByRole('dialog')).not.toBeInTheDocument();
+    expect(vi.mocked(fetch).mock.calls.some(([url]) => url === '/api/billing/cancel')).toBe(false);
+  });
+
+  it('shows continued workspace access during payment grace without an active trial', async () => {
+    renderPastDue(true);
+
+    expect(
+      await screen.findByText('Workspace access remains available while you resolve your payment.')
+    ).toBeInTheDocument();
+    expect(screen.queryByText('Billing access has ended.')).not.toBeInTheDocument();
+    expect(screen.queryByText('Free trial, no card required.')).not.toBeInTheDocument();
+  });
+
+  it('shows access has ended when payment grace has expired and no trial remains', async () => {
+    renderPastDue(false);
+
+    expect(await screen.findByText('Billing access has ended.')).toBeInTheDocument();
+    expect(
+      screen.queryByText('Workspace access remains available while you resolve your payment.')
+    ).not.toBeInTheDocument();
+    expect(screen.queryByText('Free trial, no card required.')).not.toBeInTheDocument();
+  });
+});