The payoff simulation reported months_to_freedom by taking Math.max over each
debt's payoff month — but a debt whose minimum never overcomes its interest (and
that the rolling snowball can't cover) never reaches $0, so its "never" counted
as 0 and the projection showed the OTHER debts' last month as the freedom date.
Now months_to_freedom/payoff_date are null when any active debt never clears, the
result is flagged capped, and each such debt is marked never_paid
(services/snowballService.js + the same guard in aprService calculateMinimumOnly).
Also adds tests/snowballMath.test.js (12) — the debt-payoff engine had zero
coverage. Hand-calculated examples for amortization (0% + 12% APR), snowball
rolling, avalanche vs snowball interest, skip reasons, APR snapshot, and the
unpayable-debt edge. Server suite 151 pass.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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