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>

backend/app/services/analytics_service.py

@@ -114,6 +114,18 @@ class ParentYearBalance:
       purely to the over-cap cause (e.g. earned 30, floor 20, used 15 →
       5 days over-cap lost) while the dashboard showed "Expiring 0" — that
       silent gap is why the breakdown exists now.
+    - `earned` for a year with no `vacation_days` row depends on whether the
+      year is in the past relative to `current_year` (the caller's "now").
+      `year >= current_year` assumes the full statutory entitlement, same as
+      always — unconfirmed (`is_assumed=True`), but a forward-looking guess.
+      `year < current_year` instead assumes only the floor was earned, so
+      `current_year_saveable` is `max(floor - floor, 0) = 0` and
+      `carried_out = min(left, old_carry_forward)` — a past year with no row
+      never phantom-banks days the user never told us they saved. Settings
+      offers editable rows back to the child's birth year precisely so a
+      genuine past figure can replace this assumption. A row the user DID
+      enter for a past year is untouched by this rule: `earned` is always
+      that row's `total_days`, regardless of year.
 
     `saved_days_in` on a `vacation_days` row is normally only used to *seed*
     the bank for the first year of the series (year-earned = year − 1, since
@@ -352,7 +364,7 @@ class AnalyticsService:
                 vacation_use_by_year[d.date.year] = vacation_use_by_year.get(d.date.year, 0) + 1
 
         vacation_balances = self._vacation_year_series(
-            years, vacation_by_year, vacation_use_by_year, floor
+            years, vacation_by_year, vacation_use_by_year, floor, date.today().year
         )
 
         fp_rows = [
@@ -387,9 +399,12 @@ class AnalyticsService:
         vacation_by_year: dict[int, VacationDays],
         use_by_year: dict[int, int],
         floor: int,
+        current_year: int,
     ) -> list[VacationYearBalance]:
         """FIFO carry-forward bank simulation — see `ParentYearBalance`'s
-        docstring for the full algorithm this implements."""
+        docstring for the full algorithm this implements, including the
+        past-vs-current-year `earned` rule (`current_year`) applied below for
+        a year with no entered `vacation_days` row."""
         carry_years = settings.rules.vacation_carry_forward_years
         default_earned = settings.rules.statutory_vacation_days_per_year
         # (year_earned, remaining_count) entries, oldest first.
@@ -398,7 +413,17 @@ class AnalyticsService:
 
         for i, year in enumerate(years):
             row = vacation_by_year.get(year)
-            earned = row.total_days if row is not None else default_earned
+            if row is not None:
+                earned = row.total_days
+            elif year >= current_year:
+                earned = default_earned
+            else:
+                # Past year, no entered row: assume only the floor was
+                # earned/used, not the full statutory default — see
+                # `ParentYearBalance`'s docstring. Keeps a phantom past year
+                # from banking `default_earned - floor` days the user never
+                # actually saved.
+                earned = floor
             is_assumed = row is None
 
             if i == 0: