fix(analytics): нереалистичная годовая доходность не валит пересчёт метрик

XIRR за несколько дней истории даёт артефакт солвера за ±100 000 000 %, который переполнял NUMERIC(24,10) и ронял весь refresh. Такое значение теперь считается «нет ответа».

backend/src/fintracker/analytics/returns.py

@@ -58,6 +58,10 @@ ZERO = Decimal(0)
 ONE = Decimal(1)
 DAYS_IN_YEAR = Decimal(365)
 RATE_PLACES = Decimal("0.000001")
+MAX_ABS_RATE = Decimal(10**6)
+"""An annualised rate beyond ±100 000 000 % is a solver artefact (a few days of history, or
+flows with several sign changes), not a return. It is reported as «no answer»: stored, it would
+also overflow the NUMERIC(24,10) column and take the whole metrics refresh down with it."""
 
 PERIODS: tuple[str, ...] = ("1m", "3m", "6m", "ytd", "1y", "3y", "all")
 
@@ -205,7 +209,10 @@ def annualize(cumulative: Decimal | None, days: int) -> Decimal | None:
 
 def _as_rate(value: float) -> Decimal | None:
     try:
-        return _quantize(Decimal(repr(value)))
+        rate = Decimal(repr(value))
+        if not rate.is_finite() or abs(rate) > MAX_ABS_RATE:
+            return None
+        return _quantize(rate)
     except (InvalidOperation, ValueError):
         return None
 

backend/tests/analytics/test_returns.py

@@ -119,3 +119,15 @@ def test_period_start(period: str, expected: date | None):
 def test_months_back_clamps_to_a_shorter_month():
     assert months_back(date(2026, 3, 31), 1) == date(2026, 2, 28)
     assert months_back(date(2026, 1, 15), 13) == date(2024, 12, 15)
+
+
+def test_a_rate_no_column_could_hold_is_no_answer():
+    # doubling in one day annualises to 2**365 - 1: arithmetically right, and not a return
+    assert xirr([day(0), day(1)], [D("-1000"), D("2000")]) is None
+
+
+def test_a_large_but_plausible_rate_is_kept():
+    # +10 % in a month is roughly +214 % a year
+    rate = xirr([day(0), day(30)], [D("-1000"), D("1100")])
+    assert rate is not None
+    assert D("2.0") < rate < D("2.3")