sdxc-dates

What problem does it solve? Date handling breaks when time zones are implicit, locale formatting is inconsistent, or invalid strings silently produce Invalid Date objects. This Skill documents the @sdxc/dates package, which forces every calendar question to name its IANA time zone, formats every human-facing string through Intl, and returns Result types from parsers instead of throwing. ## Core Features & Use Cases - Locale-aware formatting: formatDate, formatTime, formatRelative, formatDuration, and formatParts render timestamps through cached Intl formatters for any locale and zone. - Calendar math and day grids: startOfDay, endOfDay, diffInDays, eachDayOfInterval, daysOfYear, lastNDays, and groupByWeek build day buckets, month views, and rolling N-day windows aligned to the reader's calendar. - Safe parsing and day keys: toDayKey and fromDayKey convert between instants and YYYY-MM-DD segments, while parseDate and parseDayKey return Result values instead of Invalid Date. - Use Case: When bucketing activity rows by day for a contribution graph, group on toDayKey with the reader's zone so each cell lands on their calendar rather than the server's. ## Quick Start Add @sdxc/dates as a workspace dependency and ask the agent to format a timestamp for a reader in a specific locale and IANA time zone using formatDate or formatRelative.