objectstack-ai
diff --git a/‎.changeset/20599-utc-instant-from-parts.md‎
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diff --git a/‎packages/core/src/utils/datetime-year-below-100.test.ts‎
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+---
+"@objectstack/core": minor
+"@objectstack/service-analytics": patch
+"@objectstack/trigger-schedule": patch
+---
+
+fix(core): a date or time in the years 0001..0099 is read as written, not as 1900..1999, wherever a UTC instant is built from year / month / day / time parts
+
+`Date.UTC(year, …)` and `new Date(year, …)` read a year from 0 to 99 as 1900 + year. Core built its instants from parts that way, so every day of the years 0001..0099 (inside the supported range 0001..9999) landed in the 1900s at the sites below, with no error.
+
+- `@objectstack/core`: **new export** `wallClockToUtcMs(parts)`, the epoch milliseconds of a `WallClockParts` read as UTC. It is `Date.UTC` without the two-digit-year remap: `month` is 1-12, omitted time components are 0, and every component rolls over past its end as `Date.UTC` rolls it (`month: 13` is next January, `day: 0` the previous month's last day, `hour: 24` the next midnight). A `NaN` component gives `NaN`. Every site below now builds through it:
+  - `zonedWallClockToUtcMs` and `zonedDateStartToUtcMs`, the wall clock and the zone-offset read. The offset read also takes the zone's era, so a wall clock early on 0001-01-01 in a zone west of UTC, whose offset probe lands in year 0, reads right.
+  - `bucketKeyToCalendarRange` (`0050` spans 0050-01-01..0051-01-01, not 1950..1951; `0050-01-01` as a `day` key is no longer `null`) and `bucketDateKey`'s ISO week (0050-01-01 is in week 52 of 0049, not of 1949).
+  - The date macros: `{1976_years_ago}` resolves to `0050-09-30`, not `1950-09-30`. A macro that lands in 0001..0999 is now spelled with a four-digit year, as the `date` storage form spells it (`0055-06-15`, not `55-06-15`, which names no day).
+- `@objectstack/service-analytics`: the preview evaluator's `week` key and the `compareTo` bucket alignment build their days through `wallClockToUtcMs`.
+- `@objectstack/trigger-schedule`: a time-relative window's day bounds build through `wallClockToUtcMs`.
+
+What an author sees: `POST /api/v1/data/:object/import` stores the `datetime` cell `0050-01-01 10:00` as `0050-01-01T10:00:00.000Z`, and in `Asia/Shanghai` as `0050-01-01T01:54:17.000Z` (the zone's local mean time for that year). Before, it stored `1950-01-01T10:00:00.000Z` and `1950-01-01T02:00:00.000Z` and reported the row `ok`. Measured through the import route and read back through `POST /api/v1/data/:object/query` on SQLite and PostgreSQL 16; the `2026-07-15 10:00` control is stored the same before and after. Every year from 0100 on builds exactly as before.
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+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+//
+// [#20599] Wherever core builds a UTC instant from year / month / day / time
+// parts, a year from 0001 to 0099 is read as itself. `Date.UTC(year, …)` and
+// `new Date(year, …)` read a year from 0 to 99 as 1900 + year (ECMA-262
+// `MakeFullYear`); `wallClockToUtcMs` does not, and every site in this file
+// builds through it.
+//
+// Pins: 0001, 0050 and 0099 (the remapped years), 0100 (the first year
+// `Date.UTC` reads as written) and a 2026 control, in UTC and in Asia/Shanghai
+// wherever the site takes a zone. Every expected instant is spelled as an ISO
+// string, never computed by the code under test. Before 1901 the tz database
+// gives Asia/Shanghai its local mean time, +08:05:43, and America/New_York
+// −04:56:02: that is the offset a wall clock in those years is read at.
+
+import { describe, it, expect, beforeEach, afterAll } from 'vitest';
+import {
+  wallClockToUtcMs,
+  zonedWallClockToUtcMs,
+  zonedDateStartToUtcMs,
+  bucketDateKey,
+  bucketKeyToCalendarRange,
+} from './datetime.js';
+
+const isoOf = (ms: number) => new Date(ms).toISOString();
+
+const YEARS = ['0001', '0050', '0099', '0100', '2026'] as const;
+
+// Every pin runs on a UTC host and on an Asia/Shanghai host: the sites read
+// UTC components only, and the answer must not move with the process zone.
+const HOSTS = ['UTC', 'Asia/Shanghai'] as const;
+const originalTz = process.env.TZ;
+afterAll(() => {
+  if (originalTz === undefined) delete process.env.TZ;
+  else process.env.TZ = originalTz;
+});
+
+describe.each(HOSTS)('on a %s host', (host) => {
+  beforeEach(() => {
+    process.env.TZ = host;
+    expect(Intl.DateTimeFormat().resolvedOptions().timeZone).toBe(host);
+  });
+
+  describe('[#20599] wallClockToUtcMs builds a UTC instant with the year as written', () => {
+    it.each(YEARS)('%s-01-01 is midnight UTC of that year', (y) => {
+      expect(isoOf(wallClockToUtcMs({ year: Number(y), month: 1, day: 1 }))).toBe(`${y}-01-01T00:00:00.000Z`);
+    });
+
+    it.each(YEARS)('%s-06-15 10:20:30.456 keeps every time component', (y) => {
+      const ms = wallClockToUtcMs({ year: Number(y), month: 6, day: 15, hour: 10, minute: 20, second: 30, millisecond: 456 });
+      expect(isoOf(ms)).toBe(`${y}-06-15T10:20:30.456Z`);
+    });
+
+    it('answers exactly what Date.UTC answers from year 100 on', () => {
+      for (const [year, month, day, hour, minute, second, ms] of [
+        [100, 1, 1, 0, 0, 0, 0],
+        [999, 12, 31, 23, 59, 59, 999],
+        [2026, 7, 15, 10, 0, 0, 0],
+        [9999, 12, 31, 23, 59, 59, 999],
+      ]) {
+        expect(wallClockToUtcMs({ year, month, day, hour, minute, second, millisecond: ms })).toBe(
+          Date.UTC(year, month - 1, day, hour, minute, second, ms),
+        );
+      }
+    });
+
+    // H5: the rollover is load-bearing — `bucketKeyToCalendarRange` ends Q4 and
+    // December at month 13, and `filter-tokens` counts a month's days as day 0 of
+    // the next. The helper rolls every component over as `Date.UTC` does.
+    describe('rolls every component over past its end, as Date.UTC does', () => {
+      it.each([
+        ['month 13 is January of the next year', { year: 50, month: 13, day: 1 }, '0051-01-01T00:00:00.000Z'],
+        ['month 0 is December of the previous year', { year: 50, month: 0, day: 1 }, '0049-12-01T00:00:00.000Z'],
+        ['day 0 is the last day of the previous month', { year: 50, month: 3, day: 0 }, '0050-02-28T00:00:00.000Z'],
+        ['day 0 of March is February 29 in a leap year', { year: 48, month: 3, day: 0 }, '0048-02-29T00:00:00.000Z'],
+        ['day 32 of December runs into the next year', { year: 50, month: 12, day: 32 }, '0051-01-01T00:00:00.000Z'],
+        ['February 29 of a common year is March 1', { year: 50, month: 2, day: 29 }, '0050-03-01T00:00:00.000Z'],
+        ['hour 24 is the next midnight', { year: 99, month: 12, day: 31, hour: 24 }, '0100-01-01T00:00:00.000Z'],
+        ['hour −1 is the previous evening', { year: 50, month: 1, day: 1, hour: -1 }, '0049-12-31T23:00:00.000Z'],
+        ['day 0 of January of year 1 is the last day of year 0', { year: 1, month: 1, day: 0 }, '0000-12-31T00:00:00.000Z'],
+      ])('%s', (_label, parts, expected) => {
+        expect(isoOf(wallClockToUtcMs(parts))).toBe(expected);
+      });
+
+      it('rolls the 2026 control exactly as Date.UTC does', () => {
+        expect(wallClockToUtcMs({ year: 2026, month: 13, day: 1 })).toBe(Date.UTC(2026, 12, 1));
+        expect(wallClockToUtcMs({ year: 2026, month: 3, day: 0 })).toBe(Date.UTC(2026, 2, 0));
+        expect(wallClockToUtcMs({ year: 2026, month: 12, day: 32 })).toBe(Date.UTC(2026, 11, 32));
+        expect(wallClockToUtcMs({ year: 2026, month: 1, day: 1, hour: 24 })).toBe(Date.UTC(2026, 0, 1, 24));
+      });
+    });
+
+    it('answers NaN for a NaN or non-finite component, as Date.UTC does', () => {
+      expect(wallClockToUtcMs({ year: Number.NaN, month: 1, day: 1 })).toBeNaN();
+      expect(wallClockToUtcMs({ year: 2026, month: Number.NaN, day: 1 })).toBeNaN();
+      expect(wallClockToUtcMs({ year: 2026, month: 1, day: Number.NaN })).toBeNaN();
+      expect(wallClockToUtcMs({ year: 2026, month: 1, day: 1, hour: Number.NaN })).toBeNaN();
+      expect(wallClockToUtcMs({ year: Number.POSITIVE_INFINITY, month: 1, day: 1 })).toBeNaN();
+    });
+  });
+
+  describe('[#20599] zonedWallClockToUtcMs reads a year below 100 as written', () => {
+    it.each(YEARS)('%s-01-01 10:00 with no zone, UTC or an unknown zone is 10:00 UTC that day', (y) => {
+      for (const tz of [undefined, 'UTC', 'Not/AZone']) {
+        expect(isoOf(zonedWallClockToUtcMs({ year: Number(y), month: 1, day: 1, hour: 10 }, tz))).toBe(
+          `${y}-01-01T10:00:00.000Z`,
+        );
+      }
+    });
+
+    it.each([
+      ['0001', '0001-01-01T01:54:17.000Z'],
+      ['0050', '0050-01-01T01:54:17.000Z'],
+      ['0099', '0099-01-01T01:54:17.000Z'],
+      ['0100', '0100-01-01T01:54:17.000Z'],
+      ['2026', '2026-01-01T02:00:00.000Z'],
+    ])('%s-01-01 10:00 in Asia/Shanghai is read at that year\'s offset', (y, expected) => {
+      expect(isoOf(zonedWallClockToUtcMs({ year: Number(y), month: 1, day: 1, hour: 10 }, 'Asia/Shanghai'))).toBe(expected);
+    });
+
+    it('keeps the last second of 0099 in 0099 in Asia/Shanghai', () => {
+      const ms = zonedWallClockToUtcMs({ year: 99, month: 12, day: 31, hour: 23, minute: 59, second: 59 }, 'Asia/Shanghai');
+      expect(isoOf(ms)).toBe('0099-12-31T15:54:16.000Z');
+    });
+
+    // The offset read probes the zone at the wall clock taken as UTC. Early on
+    // 0001-01-01 in a zone west of UTC that probe is still in year 0, whose
+    // `Intl` year part is the era year `1` (1 BC): read without its era, the
+    // probe would be a year off and so would the answer.
+    it('reads 0001-01-01 in America/New_York, where the offset probe lands in year 0', () => {
+      expect(isoOf(zonedWallClockToUtcMs({ year: 1, month: 1, day: 1 }, 'America/New_York'))).toBe(
+        '0001-01-01T04:56:02.000Z',
+      );
+      expect(isoOf(zonedWallClockToUtcMs({ year: 1, month: 1, day: 1, hour: 3 }, 'America/New_York'))).toBe(
+        '0001-01-01T07:56:02.000Z',
+      );
+      expect(isoOf(zonedWallClockToUtcMs({ year: 2026, month: 1, day: 1 }, 'America/New_York'))).toBe(
+        '2026-01-01T05:00:00.000Z',
+      );
+    });
+  });
+
+  describe('[#20599] zonedDateStartToUtcMs', () => {
+    it.each(YEARS)('%s-01-01 begins at midnight UTC with no zone and in UTC', (y) => {
+      expect(isoOf(zonedDateStartToUtcMs(`${y}-01-01`))).toBe(`${y}-01-01T00:00:00.000Z`);
+      expect(isoOf(zonedDateStartToUtcMs(`${y}-01-01`, 'UTC'))).toBe(`${y}-01-01T00:00:00.000Z`);
+    });
+
+    it.each([
+      ['0001', '0000-12-31T15:54:17.000Z'],
+      ['0050', '0049-12-31T15:54:17.000Z'],
+      ['0099', '0098-12-31T15:54:17.000Z'],
+      ['0100', '0099-12-31T15:54:17.000Z'],
+      ['2026', '2025-12-31T16:00:00.000Z'],
+    ])('%s-01-01 begins at Asia/Shanghai midnight', (y, expected) => {
+      expect(isoOf(zonedDateStartToUtcMs(`${y}-01-01`, 'Asia/Shanghai'))).toBe(expected);
+    });
+  });
+
+  describe('[#20599] bucketDateKey(week) puts a day in 0001..0099 in its own ISO week', () => {
+    // A key's year below 1000 is spelled unpadded (`49-W52`): the unpadded-key
+    // family, which this card leaves alone. So the key is read as numbers here,
+    // whatever its padding, and asserted as the ISO week of the day.
+    const weekOf = (key: string | null) => {
+      const m = /^(\d+)-W(\d{2})$/.exec(String(key));
+      return m ? { year: Number(m[1]), week: Number(m[2]) } : key;
+    };
+
+    it.each([
+      ['0001-01-01T10:00:00.000Z', { year: 1, week: 1 }],
+      ['0050-01-01T10:00:00.000Z', { year: 49, week: 52 }],
+      ['0050-06-15T10:00:00.000Z', { year: 50, week: 24 }],
+      ['0099-12-31T10:00:00.000Z', { year: 99, week: 53 }],
+      ['0100-01-04T10:00:00.000Z', { year: 100, week: 1 }],
+      ['2026-06-15T10:00:00.000Z', { year: 2026, week: 25 }],
+    ])('%s in UTC', (instant, expected) => {
+      expect(weekOf(bucketDateKey(instant, 'week'))).toEqual(expected);
+      expect(weekOf(bucketDateKey(instant, 'week', 'UTC'))).toEqual(expected);
+    });
+
+    it.each([
+      // Sunday 0050-01-02 in UTC is Monday 0050-01-03 in Shanghai: week 1 of 0050.
+      ['0050-01-02T20:00:00.000Z', { year: 49, week: 52 }, { year: 50, week: 1 }],
+      ['0001-01-07T20:00:00.000Z', { year: 1, week: 1 }, { year: 1, week: 2 }],
+      ['0099-12-31T20:00:00.000Z', { year: 99, week: 53 }, { year: 99, week: 53 }],
+      ['2026-06-14T20:00:00.000Z', { year: 2026, week: 24 }, { year: 2026, week: 25 }],
+    ])('%s in UTC and in Asia/Shanghai', (instant, utc, shanghai) => {
+      expect(weekOf(bucketDateKey(instant, 'week'))).toEqual(utc);
+      expect(weekOf(bucketDateKey(instant, 'week', 'Asia/Shanghai'))).toEqual(shanghai);
+    });
+  });
+
+  describe('[#20599] bucketKeyToCalendarRange spans a key in 0001..0099 in its own year', () => {
+    it.each([
+      ['0001', '0001-01-01', '0002-01-01'],
+      ['0050', '0050-01-01', '0051-01-01'],
+      ['0099', '0099-01-01', '0100-01-01'],
+      ['0100', '0100-01-01', '0101-01-01'],
+      ['2026', '2026-01-01', '2027-01-01'],
+    ])('year %s', (key, start, end) => {
+      expect(bucketKeyToCalendarRange(key, 'year')).toEqual({ start, end });
+    });
+
+    it.each([
+      ['0001-Q2', '0001-04-01', '0001-07-01'],
+      ['0050-Q1', '0050-01-01', '0050-04-01'],
+      ['0050-Q4', '0050-10-01', '0051-01-01'],
+      ['0099-Q4', '0099-10-01', '0100-01-01'],
+      ['0100-Q4', '0100-10-01', '0101-01-01'],
+      ['2026-Q4', '2026-10-01', '2027-01-01'],
+    ])('quarter %s', (key, start, end) => {
+      expect(bucketKeyToCalendarRange(key, 'quarter')).toEqual({ start, end });
+    });
+
+    it.each([
+      ['0001-02', '0001-02-01', '0001-03-01'],
+      ['0050-01', '0050-01-01', '0050-02-01'],
+      ['0050-12', '0050-12-01', '0051-01-01'],
+      ['0099-12', '0099-12-01', '0100-01-01'],
+      ['0100-12', '0100-12-01', '0101-01-01'],
+      ['2026-12', '2026-12-01', '2027-01-01'],
+    ])('month %s', (key, start, end) => {
+      expect(bucketKeyToCalendarRange(key, 'month')).toEqual({ start, end });
+    });
+
+    it.each([
+      ['0001-01-01', '0001-01-02'],
+      ['0048-02-29', '0048-03-01'],
+      ['0050-01-01', '0050-01-02'],
+      ['0050-12-31', '0051-01-01'],
+      ['0099-12-31', '0100-01-01'],
+      ['0100-01-01', '0100-01-02'],
+      ['2026-02-28', '2026-03-01'],
+    ])('day %s', (key, end) => {
+      expect(bucketKeyToCalendarRange(key, 'day')).toEqual({ start: key, end });
+    });
+
+    it('still refuses an impossible day in 0001..0099 rather than rolling it over', () => {
+      expect(bucketKeyToCalendarRange('0050-02-29', 'day')).toBeNull(); // 0050 is not a leap year
+      expect(bucketKeyToCalendarRange('0099-04-31', 'day')).toBeNull();
+      expect(bucketKeyToCalendarRange('0100-02-29', 'day')).toBeNull(); // 0100 is not a leap year
+      expect(bucketKeyToCalendarRange('2026-02-29', 'day')).toBeNull();
+    });
+
+    // The week arm validates a reconstructed Monday against the week LABEL,
+    // which is spelled unpadded below the year 1000 (the unpadded-key family,
+    // left alone here), so it is pinned on the 2026 control only.
+    it('week 2026-W01 (the control)', () => {
+      expect(bucketKeyToCalendarRange('2026-W01', 'week')).toEqual({ start: '2025-12-29', end: '2026-01-05' });
+    });
+  });
+});