fix(salary): book lonevaxling pension provision from frozen run snapshot (#1382)

The book flow never populated pension_contribution/pension_slp, so a
gross_deduction_pension line item reduced the salary entry but the
7410/2740 pension provision and 7533/2514 SLP lines were never posted.
Derive both at the createSalaryRunEntries boundary from the run's frozen
calculation_params.slpRate snapshot so the dashboard, MCP and v1 booking
paths all emit the pension verifikat, and reuse the exact 1.058 factor
via calculateLoneVaxlingPensionProvision shared with the planning
calculator.

Fixes #317

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

app/api/v1/companies/[companyId]/salary-runs/[id]/__tests__/lifecycle.test.ts

@@ -421,6 +421,7 @@ describe('POST /salary-runs/:id/book', () => {
     total_net: 25500,
     total_avgifter: 10997,
     total_vacation_accrual: 0,
+    calculation_params: { slpRate: 0.2426 },
   }
 
   const employeeRow = {
@@ -478,6 +479,12 @@ describe('POST /salary-runs/:id/book', () => {
     expect(body.data.entry_ids).toEqual(['je_salary', 'je_avg'])
     expect(body.meta.audit.voucher_number).toBe('L2026-0023')
     expect(body.meta.audit.voucher_url).toContain('je_salary')
+    expect(mocks.createSalaryRunEntries).toHaveBeenCalledWith(
+      expect.anything(),
+      COMPANY_ID,
+      USER_ID,
+      expect.objectContaining({ calculation_params: { slpRate: 0.2426 } }),
+    )
   })
 
   it('returns PERIOD_LOCKED before invoking the engine when payment_date is locked', async () => {

app/api/v1/companies/[companyId]/salary-runs/[id]/book/route.ts

@@ -190,8 +190,16 @@ export const POST = withApiV1<{ params: Promise<{ companyId: string; id: string
             'salary (gross + tax withholding + net payment)',
             'arbetsgivaravgifter',
             ...(totalVacation > 0 || totalVacationAvgifter > 0 ? ['vacation accrual'] : []),
-            // Pension cannot be detected without the engine: we'd need
-            // to inspect line_items for löneväxling. Omitted from preview.
+            ...((employees as Array<{ line_items: Array<{ item_type: string; amount: number }> | null }>).some(
+              (employee) =>
+                (employee.line_items || []).some(
+                  (line) =>
+                    line.item_type === 'gross_deduction_pension' &&
+                    Math.round(Math.abs(line.amount) * 100) !== 0,
+                ),
+            )
+              ? ['pension provision and SLP']
+              : []),
           ],
           note: 'A live call posts 2-4 verifikationer atomically via createSalaryRunEntries. Voucher numbers are assigned at commit time.',
         },
@@ -234,6 +242,7 @@ export const POST = withApiV1<{ params: Promise<{ companyId: string; id: string
         total_net: (run as { total_net: number }).total_net,
         total_avgifter: (run as { total_avgifter: number }).total_avgifter,
         total_vacation_accrual: (run as { total_vacation_accrual: number }).total_vacation_accrual,
+        calculation_params: (run as { calculation_params: Record<string, unknown> | null }).calculation_params,
         employees: (employees as EmpRow[]).map((sre) => ({
           employee_id: sre.employee_id,
           employment_type: sre.employee?.employment_type || 'employee',