fix(salary): declare, book and pay AGI in whole kronor (SKV per-sats computation) (#1611)

* fix(salary): declare, book and pay AGI in whole kronor (SKV per-sats computation)

A user's first lönekörning surfaced öre amounts in the AGI payable while
Skatteverket deals in whole kronor. Three connected defects:

- the AGI XML rounded amounts (Math.round); öretal bortfaller (SFF
  2011:1261 22 kap. 1 §) requires truncation, and FK487 must be
  Skatteverket's own per-sats computation on the whole-krona underlag sums
  (IK587, kontroll B_006), not a truncation of the öre-exact engine sum
- the salary booking credited 2731 with exact öre, leaving a residual
  after the whole-krona skattekonto draw; 2731 now carries the declared
  amount with the remainder on 3740 (Öres- och kronutjämning)
- the LB payment file and TaxPaymentPanel paid/showed öre; they now use
  the declared whole-krona totals stored on agi_declarations (which also
  lets skattekonto auto-settlement match the draw); legacy öre rows keep
  paying öre-exact so pre-deploy bookings still clear 2731

New lib/salary/declared-avgifter.ts implements the SKV computation (per-IU
whole-krona underlag, per-sats sums, youth/växa cap splits, exact integer
math) shared by the AGI generator, the booking split and the preview.
Review overrides route all legs through the same per-category truncation;
basis overrides are inert on money totals (they never reach the filed
IUs); the v1 book route gains override parity with book-run; F-skatt rows
ignore avgifter overrides on every surface. Booked runs show their posted
verifikat instead of a recomputed projection. tax_withheld_override
requires whole kronor. Adversarially verified over three /skeptic rounds.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* chore: merge origin/main and re-ratchet the öre-round baseline

The merge brought #1609 (net-pay öresavrundning) whose two new
Math.round(x*100)/100 occurrences are counted against the baseline this
branch had tightened from 637 to 629; 631 keeps the net -6 improvement
without policing already-merged code.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(salary): address PR review (hybrid override computation, legacy youth cap, robustness)

CodeRabbit round on #1611, all findings in one pass:

- computeDeclaredAvgifterWithOverrides: one shared hybrid for the AGI
  generator AND the booking split. Overridden rows contribute their manual
  amounts per category; colleagues keep the SKV-exact per-sats underlag
  computation (a FoU override on one employee no longer costs the rest of
  the roster kronor of declared accuracy)
- youth cap keys on the RESOLVED category so legacy null-category rows
  classified as youth by the rate heuristic still get the 25k split
- F-skatt rows zero their avgifter_basis on both booking surfaces and in
  the preview, matching the AGI's isFSkattRow invariant
- preview route: posted-voucher lookup errors return 500 instead of
  masquerading as a booked run with no vouchers; 400/500 tests added
- run page clears stale AGI totals when the tax-payment fetch fails
- SalaryOverridePanel truncates the tax override to whole kronor so the
  schema's .int() cannot bounce a decimal input with a 400
- v1 book route override parity pinned by a lifecycle test
- DECISIONS.md format fixes + superseded entry marked; exempt category
  mapped explicitly; unified truncation-drift band with rationale

Declined (recorded): dating the decision entries 2026-08-13 (bot assumed
UTC; the decisions were made after midnight local time).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(salary): round-2 review nits (shared F-skatt helper, test hygiene)

- isFSkattStatus in declared-avgifter.ts: single source for the F-skatt
  exclusion, consumed by book-run, the v1 book route, the preview route and
  the AGI generator, per the Swedish review's drift-risk finding
- declared-avgifter test suite gets the standard beforeEach cleanup

Declined (recorded for the summary): auto-generated correction voucher for
regenerated legacy periods (data-repair follow-up needing Emil's go); SFF
22 kap. 1 par. citation doubt (verified against lagen.nu and already shipped
in tax-tables.ts); 3740 scope doubt (BAS generic utjamning account, Visma
praxis, matches the user's reference voucher).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

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

lib/__tests__/money.test.ts

@@ -1,5 +1,12 @@
 import { describe, it, expect } from 'vitest'
-import { roundOre, ORE_TOLERANCE, equalOre, isZeroOre, sumOre } from '@/lib/money'
+import {
+  roundOre,
+  truncateToWholeKronor,
+  ORE_TOLERANCE,
+  equalOre,
+  isZeroOre,
+  sumOre,
+} from '@/lib/money'
 
 describe('roundOre', () => {
   it('rounds exact-half öre values up where naive Math.round fails', () => {
@@ -32,6 +39,35 @@ describe('roundOre', () => {
   })
 })
 
+describe('truncateToWholeKronor', () => {
+  it('drops the öre entirely: truncation, never rounding', () => {
+    // öretal bortfaller (SFF 2011:1261 22 kap. 1 §): 16 073,84 declares and
+    // draws as 16 073, and even ,99 never rounds up.
+    expect(truncateToWholeKronor(16073.84)).toBe(16073)
+    expect(truncateToWholeKronor(16073.99)).toBe(16073)
+    expect(truncateToWholeKronor(16073.5)).toBe(16073)
+    expect(truncateToWholeKronor(0.84)).toBe(0)
+  })
+
+  it('leaves whole-krona amounts untouched', () => {
+    expect(truncateToWholeKronor(16073)).toBe(16073)
+    expect(truncateToWholeKronor(0)).toBe(0)
+  })
+
+  it('does not lose a krona to IEEE drift just below an integer', () => {
+    // 51 158 × 0,3142 style float noise: a true 16 074,00 stored as
+    // 16 073,999999999998 must not truncate to 16 073.
+    expect(truncateToWholeKronor(16073.999999999998)).toBe(16074)
+    expect(truncateToWholeKronor(6.999999999999999)).toBe(7)
+  })
+
+  it('truncates negative amounts toward zero and normalizes -0', () => {
+    expect(truncateToWholeKronor(-5.99)).toBe(-5)
+    expect(truncateToWholeKronor(-0.84)).toBe(0)
+    expect(Object.is(truncateToWholeKronor(-0.84), -0)).toBe(false)
+  })
+})
+
 describe('ORE_TOLERANCE / equalOre / isZeroOre', () => {
   it('is half an öre', () => {
     expect(ORE_TOLERANCE).toBe(0.005)