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53-week years
Some ISO years have 53 weeks (when Jan 1 is Thursday, or a leap year starts on Wednesday — e.g. 2026). Code that assumes 52 weeks misaligns year-over-year comparisons and drops a week.
Class
Case to account for
Affects
1 conversion
01
Detection
weeksInWeekYear === 53.
02
Mitigation
01
Handle 53-week years explicitly; align year-over-year by week-year, not a fixed 52-offset.
03
Affected conversions
Instant(ISO week × slot) key
OPEN