The live couple streak used a raw 48h rule that reset on any 48h gap AND
inflated the count by incrementing on every answer (several a day counted
several times). Replace with StreakCalculator.nextCount: once per calendar day,
one forgiving grace day (a single missed day still continues), reset only after
2+ missed days; skip the redundant write on a same-day answer.
Celebration milestones now include the habit-building early tiers
(1/3/7/14/30/100/365), single-sourced from StreakCalculator so the count and the
celebration can't drift; the milestone dialog handles day 1 grammatically.
Tested (StreakCountTest): same-day idempotency, consecutive, grace, reset, and
partner timezone-skew (never breaks a same-boundary streak). Existing 24
StreakCalculator tests still pass.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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