Let vacation years go back to the child's birth year

Settings only offered vacation-day rows from the current year forward,
while analytics ran its balance series from the child's birth year. Every
year in the gap had no vacation_days row, so the series assumed a full
statutory 25 earned with no use and banked earned - floor of it forward —
phantom saved days the user had no row to correct.

Settings now offers editable rows back to the birth year, and a past year
with no row assumes only the floor was earned, so it banks nothing. A past
year the user did enter is untouched by that rule.

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

frontend/src/pages/Settings.tsx

@@ -90,18 +90,30 @@ function describePartnerError(err: unknown, t: (key: TranslationKey, params?: Re
   return err instanceof Error ? err.message : fallback
 }
 
-/** Current year through (at minimum) the year the child turns 4. */
+/**
+ * The child's birth year (or the current year, if earlier/no birth date)
+ * through — at minimum — the year the child turns 4.
+ *
+ * Starting at the birth year, not `currentYear`, lets Settings offer an
+ * editable vacation-days row for every past year too — see
+ * `AnalyticsService._vacation_year_series`'s `current_year` rule, which
+ * stops assuming the full statutory default for a past year with no row
+ * precisely so a real figure can be entered here instead.
+ */
 function computeVacationYearRange(birthDate: string | undefined, currentYear: number): number[] {
+  let startYear = currentYear
   let endYear = currentYear
   if (birthDate) {
-    const fourthBirthday = new Date(birthDate)
-    if (!isNaN(fourthBirthday.getTime())) {
+    const birth = new Date(birthDate)
+    if (!isNaN(birth.getTime())) {
+      startYear = Math.min(startYear, birth.getFullYear())
+      const fourthBirthday = new Date(birthDate)
       fourthBirthday.setFullYear(fourthBirthday.getFullYear() + 4)
       endYear = Math.max(endYear, fourthBirthday.getFullYear())
     }
   }
   const years: number[] = []
-  for (let year = currentYear; year <= endYear; year++) {
+  for (let year = startYear; year <= endYear; year++) {
     years.push(year)
   }
   return years
@@ -352,6 +364,15 @@ export function Settings(): ReactNode {
     () => computeVacationYearRange(selectedChild?.birth_date, currentYear),
     [selectedChild?.birth_date, currentYear],
   )
+  // Preschool planning-day rows only ever make sense current-year forward
+  // (§Task 1 preschool reserve is a forecast, not a historical record) —
+  // `vacationYears` above was widened back to the child's birth year for
+  // the vacation-days table only, so this block gets its own slice rather
+  // than sharing it.
+  const preschoolYears = useMemo(
+    () => vacationYears.filter((year) => year >= currentYear),
+    [vacationYears, currentYear],
+  )
   // Keyed on (personalDataUuid, year), NOT year alone — with more than one
   // workspace member, matching on year alone would silently pick up
   // whichever member's row for that year happened to come first in
@@ -366,21 +387,29 @@ export function Settings(): ReactNode {
           // — the at-risk figures then default to 0 rather than block the
           // rest of this editable row on a supplementary fetch.
           const vacationBalance = projection?.yearBalances.find((b) => b.year === year)?.vacation
+          // No row entered: fall back to the SAME figure analytics assumed
+          // for this year (`AnalyticsService._vacation_year_series`'s
+          // `earned` — statutory default for a current/future year, the
+          // floor for a past one) rather than re-deriving that rule here.
+          // Only falls back further to the statutory default when analytics
+          // hasn't loaded yet, matching the pre-existing no-data behaviour.
+          const fallbackTotalDays = vacationBalance?.earned ?? DEFAULT_VACATION_DAYS
           return {
             year,
-            totalDays: existing?.totalDays ?? DEFAULT_VACATION_DAYS,
+            totalDays: existing?.totalDays ?? fallbackTotalDays,
             savedDaysIn: existing?.savedDaysIn ?? 0,
-            // §3.2 — no vacation_days row for this year yet: the statutory
+            // §3.2 — no vacation_days row for this year yet: an assumed
             // default is shown, not an entered value. Mirrors the backend's
             // `VacationBalanceResponse.is_assumed` for the propose-time table.
             isAssumed: existing === undefined,
+            isPast: year < currentYear,
             expiring: vacationBalance?.expiring ?? 0,
             expiringAge: vacationBalance?.expiringAge ?? 0,
             expiringOverCap: vacationBalance?.expiringOverCap ?? 0,
           }
         })
       }),
-    [orderedMembers, vacationYears, vacDays, analytics],
+    [orderedMembers, vacationYears, vacDays, analytics, currentYear],
   )
 
   if (isLoading) {
@@ -655,7 +684,7 @@ export function Settings(): ReactNode {
                   <h4>{t('settings.preschoolPerYearTitle')}</h4>
                   <p className="settings-panel__help">{t('settings.preschoolPerYearHelp')}</p>
                   <div className="preschool-year-rows" data-testid="preschool-year-rows">
-                    {vacationYears.map((year) => (
+                    {preschoolYears.map((year) => (
                       <PreschoolPlanningYearRow
                         key={year}
                         childId={selectedChildId}