@@ -0,0 +1,43 @@
+---
+"@objectstack/objectql": minor
+---
+
+fix(objectql)!: a `date` / `datetime` string is written on a calendar day that exists, and a `datetime` string in an ISO 8601 spelling, or it is refused with `VALIDATION_FAILED` / 400 (`invalid_date`) — `"2026-02-30T10:00:00Z"` is no longer stored as March 2, and `"07/15/2026 10:00"` is no longer read in the server's zone (#20525)
+
+Clause-②: no (narrowing)
+
+<!-- adr-0087: not-required (no-migration-prescription) a refusal of a written VALUE at the record validator's date / datetime arm: no authorable key, spelling or stored shape of metadata moves, `packages/spec` is untouched, and a stored row keeps whatever it holds. What is refused is a temporal string naming a day that does not exist, or a datetime string outside the ISO spellings, and which instant such a string meant (a host zone, a locale's day order) is not something a ledger entry can decide. The other categories are closed on facts: the package publishes (not `unpublished`); no ADR-0087 id covers a write-door value check (not `registered` / `already-registered`); and the change is runtime behaviour, not a TypeScript declaration (not `runtime-interface-only` / `type-surface-only`). -->
+
+**BREAKING**: this narrows what a `date` and a `datetime` field accept as a written value. It ships as `minor` under the launch-window convention for accept-set narrowings (`check-changeset-no-major` refuses `major` until GA; the breaking-ness is carried by this banner and the ADR-0087 disposition above).
+
+Two kinds of string are now refused with `VALIDATION_FAILED` / 400, the field code `invalid_date` and its existing message ("must be a valid date (ISO-8601)" / "must be a valid datetime (ISO-8601)"), naming the field, before anything is written:
+
+- **A day that does not exist**, as a `date` or as the day part of a `datetime`: `"2026-02-30"`, `"2026-02-29"` (2026 is not a leap year), `"2026-04-31"`, `"2026-02-30T10:00:00Z"`. `"2028-02-29"` is a real day and is accepted.
+- **A `datetime` string in any spelling but these ISO 8601 ones**, after trimming: `YYYY-MM-DD` (midnight UTC); `YYYY-MM-DDTHH:MM[:SS[.fraction]]` followed by `Z`, a `±HH:MM` or `±HHMM` offset, or nothing (a zone-naive wall clock is UTC, ADR-0074); and `YYYY-MM-DD HH:MM[:SS[.fraction]]` with no zone (UTC the same way). Refused now, for example: `"2026/07/15 10:00"`, `"07/15/2026 10:00"`, `"15 July 2026 10:00"`, `"07/08/2026"`, `"2026-07-15 10:00 PM"`, `"Wed, 15 Jul 2026 10:00:00 GMT"`, `"2026"`, `"2026-07"`, `"2026-07-15t10:00:00z"` (lower case), `"+002026-07-15T10:00:00Z"`, and a space-separated time carrying a zone, `"2026-07-15 10:00:00+08:00"` (write it with a `T`).
+
+The fix is to send the value in one of those spellings — `"2026-07-15T10:00:00Z"`, `"2026-07-15T10:00:00+08:00"` or `"2026-07-15 10:00"` — or a JS `Date`. No other spelling is read for you, on purpose: `07/08/2026` is July 8 in one locale and August 7 in another, and a wall clock with no zone was read in whatever zone the server process ran in.
+
+What a caller sees, before and after, through `POST /api/v1/data/:object` and a read-back, the process in America/New_York, PostgreSQL 16 at `Asia/Shanghai`:
+
+| written | memory | SQLite | PostgreSQL | now, on all three |
+|:--|:--|:--|:--|:--|
+| `date` `"2026-02-30"` | 201, read back `"2026-02-30"`, a day that does not exist | the same | 500 `DATABASE_ERROR` | 400 `invalid_date` |
+| `datetime` `"2026-02-30T10:00:00Z"` | 201, read back `"2026-03-02T10:00:00.000Z"` | the same | the same | 400 `invalid_date` |
+| `datetime` `"2026/07/15 10:00"`, `"07/15/2026 10:00"`, `"15 July 2026 10:00"` | 201, `"2026-07-15T14:00:00.000Z"`, the server process's zone | the same | the same | 400 `invalid_date` |
+| `datetime` `"07/08/2026"` | 201, `"2026-07-08T04:00:00.000Z"`, month-first in the process zone | the same | the same | 400 `invalid_date` |
+| `datetime` `"2026"` | 201, `"1970-01-01T00:00:02.026Z"` | the same | the same | 400 `invalid_date` |
+
+The stored instant of a non-ISO `datetime` was a property of the deployment host: the same request landed hours apart on two servers.
+
+What changes: the record validator's `date` / `datetime` arm asks two more questions of a string, on insert, update, a multi-row update and `engine.validate` (the dry run), before any driver write. Does its leading `YYYY-MM-DD` name a day that exists (month 01..12, day up to that month's length, February 29 only in a leap year)? And, for a `datetime`, is it one of the ISO spellings above? A `Date` names a real instant and keeps its answer.
+
+**Who is affected.** A caller that writes a `date` or `datetime` field as a string: a REST or SDK client, a flow, an MCP `create_record` / `update_record` call written by a model. A row that already holds such a value keeps it, since nothing re-reads stored rows. An update that omits the field is not affected; one that sends the old string back is refused, so re-write it in an ISO spelling. The server import (`POST /api/v1/data/:object/import`) turns a `datetime` cell into ISO text itself before the write, so its `datetime` cells reach this check already converted; a `date` cell naming a day that does not exist (`2026-02-30`) is now a per-row `invalid_date`, where memory and SQLite stored it and PostgreSQL failed the row.
+
+**Unchanged**, measured identical before and after on memory, SQLite and PostgreSQL through REST:
+
+- a real leap day: `date` `"2028-02-29"`, `datetime` `"2028-02-29T10:00:00Z"`;
+- each ISO spelling above, stored as the same instant: `"2026-07-15T10:00:00Z"`, `"2026-07-15T10:00:00+08:00"` (`"2026-07-15T02:00:00.000Z"`), `"2026-07-15 10:00"` and `"2026-07-15T10:00"` (`"2026-07-15T10:00:00.000Z"`, UTC, not the host zone), `"2026-07-15"` (`"2026-07-15T00:00:00.000Z"`);
+- a `date` string with a leading real `YYYY-MM-DD`, still stored as that day;
+- a `Date`, still accepted; an epoch-millisecond number, still refused with `invalid_date`;
+- the year range 0001..9999;
+- every `time` value, and every filter comparand (`where`, a per-aggregation `filter`, `having`).
@@ -0,0 +1,78 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * [#20525] What the temporal write door admits, this driver stores as written:
+ * a leap day as that day, and each ISO `datetime` spelling as the instant it
+ * names — the same instant whatever the server process's zone.
+ *
+ * The engine's record validator now refuses a string whose leading
+ * `YYYY-MM-DD` names a day that does not exist, and a `datetime` string outside
+ * the ISO spellings the storage rule reads the same on every host, with
+ * `VALIDATION_FAILED` / `invalid_date` before any driver write
+ * (`packages/objectql/src/engine-temporal-write-real-day-iso.test.ts`). The
+ * refusal is therefore not this driver's; what it owes is the other half: every
+ * spelling the door admits is STORED as the value it names and found by it,
+ * with the process in a zone that is not UTC so a host-zone reading would show.
+ *
+ * Measured on the base through REST over this driver, the process in
+ * America/New_York: `datetime` `"2026-02-30T10:00:00Z"` was stored as
+ * `"2026-03-02T10:00:00.000Z"`, `"2026/07/15 10:00"` as
+ * `"2026-07-15T14:00:00.000Z"`, and `date` `"2026-02-30"` verbatim. The engine
+ * refuses those now; the REST door over SQL is
+ * `packages/rest/src/data-temporal-write-real-day-iso.test.ts`.
+ */
+
+import { afterAll, beforeAll, describe, expect, it } from 'vitest';
+import { InMemoryDriver } from './memory-driver.js';
+
+const OBJECT = 'ledger_temporal_20525';
+const FIELDS = { placed_on: { type: 'date' }, opened_at: { type: 'datetime' } };
+const HOST_ZONE = 'America/New_York';
+
+/** Each `datetime` spelling the write door admits → the instant it names, in UTC. */
+const ADMITTED_DATETIME: ReadonlyArray<readonly [string, unknown, string]> = [
+  ['leap', '2028-02-29T10:00:00Z', '2028-02-29T10:00:00.000Z'],
+  ['utc', '2026-07-15T10:00:00Z', '2026-07-15T10:00:00.000Z'],
+  ['offset', '2026-07-15T18:00:00+08:00', '2026-07-15T10:00:00.000Z'],
+  ['naive-t', '2026-07-15T10:00', '2026-07-15T10:00:00.000Z'],
+  ['naive-space', '2026-07-15 10:00:00', '2026-07-15T10:00:00.000Z'],
+  ['a-date', new Date(Date.UTC(2026, 6, 15, 10)), '2026-07-15T10:00:00.000Z'],
+];
+
+const originalTz = process.env.TZ;
+
+describe('[#20525] every temporal spelling the write door admits is stored as the value it names', () => {
+  let driver: InMemoryDriver;
+
+  beforeAll(async () => {
+    process.env.TZ = HOST_ZONE;
+    expect(Intl.DateTimeFormat().resolvedOptions().timeZone, 'the host zone really changed').toBe(HOST_ZONE);
+    driver = new InMemoryDriver({});
+    await driver.connect();
+    await driver.syncSchema(OBJECT, { name: OBJECT, fields: FIELDS });
+    for (const [id, opened_at] of ADMITTED_DATETIME) await driver.create(OBJECT, { id, opened_at });
+    await driver.create(OBJECT, { id: 'leap-day', placed_on: '2028-02-29' });
+    await driver.create(OBJECT, { id: 'before', placed_on: '2028-02-28', opened_at: '2026-07-15T09:59:59Z' });
+  });
+
+  afterAll(() => {
+    if (originalTz === undefined) delete process.env.TZ;
+    else process.env.TZ = originalTz;
+  });
+
+  it('reads each datetime back as its UTC instant, and the leap day as itself', async () => {
+    for (const [id, , instant] of ADMITTED_DATETIME) {
+      expect((await driver.findOne(OBJECT, { where: { id } }))?.opened_at, id).toBe(instant);
+    }
+    expect((await driver.findOne(OBJECT, { where: { id: 'leap-day' } }))?.placed_on).toBe('2028-02-29');
+  });
+
+  it('finds each one by the instant it names, and orders it after the second before', async () => {
+    const ids = async (where: Record<string, unknown>) =>
+      (await driver.find(OBJECT, { where })).map((r) => r.id as string).sort();
+    const july = ADMITTED_DATETIME.filter(([id]) => id !== 'leap').map(([id]) => id).sort();
+    expect(await ids({ opened_at: { $eq: '2026-07-15T10:00:00Z' } })).toEqual(july);
+    expect(await ids({ opened_at: { $gt: '2026-07-15T09:59:59Z', $lt: '2027-01-01' } })).toEqual(july);
+    expect(await ids({ placed_on: { $gt: '2028-02-28' } })).toEqual(['leap-day']);
+  });
+});
@@ -0,0 +1,194 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * [#20525] A temporal string is written on a calendar day that exists, and a
+ * `datetime` string in an ISO 8601 spelling — or it is refused with
+ * `VALIDATION_FAILED` and the field's `invalid_date` code, on insert, update, a
+ * multi-row update and the dry-run `validate`, before any driver write. Never
+ * rolled over, never re-read in the server's zone.
+ *
+ * Measured on the base (`b2b6a0643`) through `POST /api/v1/data/:object` and a
+ * read-back, the process in America/New_York, PostgreSQL 16 at Asia/Shanghai:
+ *
+ * | written | memory | SQLite | PostgreSQL | now |
+ * |:--|:--|:--|:--|:--|
+ * | `date` `"2026-02-30"` | 201, `"2026-02-30"` | 201, `"2026-02-30"` | 500 `DATABASE_ERROR` | 400 |
+ * | `datetime` `"2026-02-30T10:00:00Z"` | 201, `"2026-03-02T10:00:00.000Z"` | the same | the same | 400 |
+ * | `datetime` `"2026/07/15 10:00"`, `"07/15/2026 10:00"`, `"15 July 2026 10:00"` | 201, `"2026-07-15T14:00:00.000Z"` (the process zone) | the same | the same | 400 |
+ * | `datetime` `"07/08/2026"` | 201, `"2026-07-08T04:00:00.000Z"` (month-first, the process zone) | the same | the same | 400 |
+ * | `datetime` `"2026"` | 201, `"1970-01-01T00:00:02.026Z"` | the same | the same | 400 |
+ * | `date` `"2028-02-29"`, `datetime` `"2028-02-29T10:00:00Z"` (a leap day) | 201, as written | the same | the same | unchanged |
+ * | `datetime` `"2026-07-15 10:00"` (zone-naive ISO) | 201, `"2026-07-15T10:00:00.000Z"` (UTC, ADR-0074) | the same | the same | unchanged |
+ *
+ * The REST door over real drivers is
+ * `packages/rest/src/data-temporal-write-real-day-iso.test.ts`; the memory
+ * driver's half is `memory-20525-temporal-write-real-day-iso.test.ts`. This
+ * file's driver records writes and stores nothing, because the refusal sits in
+ * front of every driver — so these verdicts hold whatever the process zone.
+ */
+
+import { describe, it, expect, beforeEach } from 'vitest';
+import { ObjectQL } from './engine.js';
+
+const ledger = {
+  name: 'ledger',
+  label: 'Ledger',
+  fields: {
+    id: { name: 'id', type: 'text' as const, primaryKey: true },
+    customer_id: { name: 'customer_id', type: 'text' as const },
+    placed_on: { name: 'placed_on', type: 'date' as const },
+    opened_at: { name: 'opened_at', type: 'datetime' as const },
+  },
+};
+
+type Field = 'placed_on' | 'opened_at';
+
+/** Arm 1 — a leading day that does not exist. Each was `Date.parse`-readable, and stored as written or rolled over at the base. */
+const IMPOSSIBLE_DAY: ReadonlyArray<readonly [Field, string]> = [
+  ['placed_on', '2026-02-30'],
+  ['placed_on', '2026-02-29'],
+  ['placed_on', '2026-04-31'],
+  ['placed_on', '2026-02-30T10:00:00Z'],
+  ['opened_at', '2026-02-30T10:00:00Z'],
+  ['opened_at', '2026-02-30'],
+  ['opened_at', '2026-02-30 10:00'],
+  ['opened_at', '2026-02-29T10:00:00Z'],
+  ['opened_at', '2026-04-31T10:00:00+08:00'],
+];
+
+/** Arm 2 — a `datetime` string in no ISO spelling the storage rule reads the same on every host. Each was a 201 at the base. */
+const NON_ISO_DATETIME: readonly string[] = [
+  '2026/07/15 10:00',
+  '07/15/2026 10:00',
+  '15 July 2026 10:00',
+  '07/08/2026',
+  '2026-07-15 10:00 PM',
+  'Wed, 15 Jul 2026 10:00:00 GMT',
+  '2026',
+  '2026-07',
+  '2026-07-15t10:00:00z',
+  '+002026-07-15T10:00:00Z',
+  '2026-07-15 10:00Z',
+  '2026-07-15 10:00:00+08:00',
+];
+
+/** Refused at the base already — kept refused. */
+const STILL_REFUSED: ReadonlyArray<readonly [Field, unknown]> = [
+  ['opened_at', 'not-a-date'],
+  ['opened_at', '2026-07-15T25:00:00Z'],
+  ['opened_at', Date.UTC(2026, 6, 15, 10)],
+  ['placed_on', '2026/07/15'],
+];
+
+/** The leap-day control and the ISO controls — each reaches the driver. */
+const ACCEPTED: ReadonlyArray<readonly [Field, unknown]> = [
+  ['placed_on', '2028-02-29'],
+  ['placed_on', '2026-02-28'],
+  ['placed_on', '2026-07-15'],
+  ['placed_on', '2026-07-15T10:00:00Z'],
+  ['placed_on', '2026-07-15 10:00'],
+  ['placed_on', ' 2026-07-15'],
+  ['placed_on', '0050-01-01'],
+  ['placed_on', new Date(Date.UTC(2026, 6, 15, 10))],
+  ['opened_at', '2028-02-29T10:00:00Z'],
+  ['opened_at', '2026-07-15'],
+  ['opened_at', '2026-07-15T10:00'],
+  ['opened_at', '2026-07-15T10:00:00'],
+  ['opened_at', '2026-07-15T10:00:00Z'],
+  ['opened_at', '2026-07-15T10:00:00.123Z'],
+  ['opened_at', '2026-07-15T10:00:00+08:00'],
+  ['opened_at', '2026-07-15T10:00:00-0530'],
+  ['opened_at', '2026-07-15 10:00'],
+  ['opened_at', '2026-07-15 10:00:00.5'],
+  ['opened_at', ' 2026-07-15 10:00'],
+  ['opened_at', '0050-01-01T10:00:00Z'],
+  ['opened_at', new Date(Date.UTC(2026, 6, 15, 10))],
+];
+
+const REFUSED: ReadonlyArray<readonly [Field, unknown]> = [
+  ...IMPOSSIBLE_DAY,
+  ...NON_ISO_DATETIME.map((v) => ['opened_at', v] as const),
+  ...STILL_REFUSED,
+];
+
+/** A driver that records every read and write, and answers none. */
+function makeRecordingDriver() {
+  const writes: Record<string, unknown>[] = [];
+  const driver: any = {
+    name: 'recording', version: '0.0.0', supports: {},
+    async connect() {}, async disconnect() {}, async checkHealth() { return true; }, async execute() { return null; },
+    async find() { return []; },
+    async findOne() { return { id: 'r1' }; },
+    async count() { return 0; },
+    async aggregate() { return []; },
+    async create(_o: string, data: Record<string, unknown>) { writes.push(data); return { ...data }; },
+    async update(_o: string, id: string, data: Record<string, unknown>) { writes.push(data); return { ...data, id }; },
+    async updateMany(_o: string, _ast: unknown, data: Record<string, unknown>) { writes.push(data); return 0; },
+    async delete() { return true; },
+    async deleteMany() { return 0; },
+    async bulkCreate(_o: string, batch: Record<string, unknown>[]) { writes.push(...batch); return batch; },
+    async beginTransaction() { return { commit: async () => {}, rollback: async () => {} }; },
+    async commit() {}, async rollback() {},
+  };
+  return { driver, writes };
+}
+
+const refusalOf = async (p: Promise<unknown>) =>
+  p.then(() => null, (e: any) => e as Error & { code?: string; status?: number; fields?: Array<{ field: string; code: string }> });
+
+const labelOf = (field: Field, value: unknown) =>
+  `${field} ${value instanceof Date ? `Date ${value.toISOString()}` : JSON.stringify(value)}`;
+
+describe('[#20525] the write door — a real calendar day, and an ISO spelling for a datetime, or VALIDATION_FAILED before any write', () => {
+  let engine: ObjectQL;
+  let writes: Record<string, unknown>[];
+
+  beforeEach(async () => {
+    const rec = makeRecordingDriver();
+    writes = rec.writes;
+    engine = new ObjectQL();
+    engine.registerDriver(rec.driver, true);
+    await engine.init();
+    engine.registry.registerObject(ledger, 'test');
+  });
+
+  const doors = (field: Field, value: unknown) => [
+    ['insert', () => engine.insert('ledger', { id: 'n1', customer_id: 'c1', [field]: value })],
+    ['update', () => engine.update('ledger', { id: 'r1', [field]: value })],
+    ['multi-row update', () => engine.update('ledger', { [field]: value }, { where: { customer_id: 'c1' }, multi: true })],
+  ] as const;
+
+  it('refuses an impossible day and a non-ISO datetime on insert, update and a multi-row update, naming the field with invalid_date — and writes nothing', async () => {
+    for (const [field, value] of REFUSED) {
+      for (const [door, call] of doors(field, value)) {
+        const err = await refusalOf(call());
+        expect(err, `${door}, ${labelOf(field, value)}`).not.toBeNull();
+        expect(err!.code, `${door}, ${labelOf(field, value)}`).toBe('VALIDATION_FAILED');
+        expect(err!.fields, `${door}, ${labelOf(field, value)}`).toEqual([expect.objectContaining({ field, code: 'invalid_date' })]);
+      }
+    }
+    expect(writes, 'no write — every refusal precedes the driver').toHaveLength(0);
+  });
+
+  it('the dry-run validate predicts each refusal — and each accepted value as valid', async () => {
+    for (const [field, value] of REFUSED) {
+      const verdict = await engine.validate('ledger', { [field]: value });
+      expect(verdict.valid, labelOf(field, value)).toBe(false);
+      expect(verdict.results[0]!.errors, labelOf(field, value)).toEqual([expect.objectContaining({ field, code: 'invalid_date' })]);
+    }
+    for (const [field, value] of ACCEPTED) {
+      expect((await engine.validate('ledger', { [field]: value })).valid, labelOf(field, value)).toBe(true);
+    }
+  });
+
+  it('accepts a leap day, the ISO spellings and a Date on every door — the POSITIVE CONTROL', async () => {
+    for (const [field, value] of ACCEPTED) {
+      for (const [door, call] of doors(field, value)) {
+        const before = writes.length;
+        await expect(call(), `${door}, ${labelOf(field, value)}`).resolves.toBeDefined();
+        expect(writes.length, `${door}, ${labelOf(field, value)} reached the driver`).toBe(before + 1);
+        expect(writes.at(-1)![field], `${door}, ${labelOf(field, value)} reached it as written`).toEqual(value);
+      }
+    }
+  });
+});