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diff --git a/‎packages/objectql/src/engine-date-write-iso-only.test.ts‎
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diff --git a/‎packages/objectql/src/validation/record-validator.ts‎
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@@ -0,0 +1,40 @@
+---
+"@objectstack/objectql": minor
+---
+
+fix(objectql)!: a `date` string is written in its `YYYY-MM-DD` form, or it is refused with `VALIDATION_FAILED` / 400 (`invalid_date`) — `"2026/07/15"` is no longer stored verbatim as a non-day (#20481)
+
+Clause-②: no (narrowing)
+
+<!-- adr-0087: not-required (no-migration-prescription) a refusal of a written VALUE at the record validator's date 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 date string without a leading YYYY-MM-DD, and which calendar day such a string meant (07/08/2026 names two) 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 The other categories are closed on facts: the package publishes (not `unpublished`); no ADR-0087 id covers a write-door value check (not `registered` / `already-registered`); and the change is runtime behaviour, not a TypeScript declaration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` field accepts 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).
+
+FROM a `date` field written as a string with no leading `YYYY-MM-DD` that `Date.parse` still reads — `"2026/07/15"`, `"07/15/2026"`, `"07/08/2026"`, `"15 July 2026"`, `"July 15, 2026"`, `"2026-7-15"`, `"2026.07.15"`, `"+002026-07-15"` → TO `VALIDATION_FAILED` / 400 with the field code `invalid_date` and its existing message, nothing written. The fix is one line: send `YYYY-MM-DD` (`"2026-07-15"`), 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 guess stores the wrong day silently.
+
+Measured through `POST /api/v1/data/:object` and a read-back, before this change, the process in America/New_York and PostgreSQL 16 at `DateStyle` `ISO, MDY`:
+
+| written to a `date` | memory | SQLite | PostgreSQL | now, on all three |
+|:--|:--|:--|:--|:--|
+| `"2026/07/15"`, `"07/15/2026"`, `"15 July 2026"`, `"2026-7-15"`, `"2026.07.15"`, `"July 15, 2026"` | 201, read back verbatim | 201, read back verbatim | 201, `"2026-07-15"` | 400 `invalid_date` |
+| `"07/08/2026"` | 201, verbatim | 201, verbatim | 201, `"2026-07-08"` (a `DMY` server reads August 7) | 400 `invalid_date` |
+| `"+002026-07-15"` | 201, verbatim | 201, verbatim | 500 | 400 `invalid_date` |
+
+A verbatim `"2026/07/15"` is not a day: it sorts and compares as text beside real days, so it falls out of every date range and every date filter. PostgreSQL's reading was its server's `DateStyle`, not the writer's.
+
+What changes:
+
+- The record validator's `date` arm asks one more question of a string: does the `date` storage rule read it? That rule (`@objectstack/core`'s `temporalStorageForm`) collapses a string with a leading `YYYY-MM-DD` to that day and hands every other string back unchanged. The question is asked through `isUninterpretableTemporalComparand`, the predicate the engine's temporal-comparand door already refuses such a `date` comparand with, so a `date` string refused on `where` is refused as a written value too. It applies on insert, update, a multi-row update and `engine.validate` (the dry run), before any driver write.
+
+**Who is affected.** A caller that writes a `date` field as a locale or free-form string: a REST or SDK client, a flow, an MCP `create_record` / `update_record` call written by a model. The server import (`POST /api/v1/data/:object/import`) is not affected: it already turns a date cell into `YYYY-MM-DD` before the write. A row that already holds such a string 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 the field as `YYYY-MM-DD`.
+
+**Unchanged**, measured identical before and after on memory, SQLite and PostgreSQL through REST:
+
+- a string with a leading `YYYY-MM-DD`, still stored as that day: `"2026-07-15"`, `"2026-07-15T10:00:00Z"`, `"2026-07-15 10:00"`, `" 2026-07-15"`;
+- a `Date`, still stored as its UTC calendar day;
+- an epoch-millisecond number, still refused with `invalid_date`;
+- a string `Date.parse` cannot read, still refused: `"20260715"`, `"15/07/2026"`;
+- the year range 0001..9999;
+- every `datetime` and `time` value.
@@ -0,0 +1,62 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * [#20481] What the `date` write door admits, this driver stores as its day.
+ *
+ * The engine's record validator now admits a `date` string only when it carries
+ * a leading `YYYY-MM-DD` — the `date` storage rule's own reading
+ * (`@objectstack/core`'s `temporalStorageForm`) — and refuses every other
+ * spelling with `VALIDATION_FAILED` / `invalid_date` before any driver write
+ * (`packages/objectql/src/engine-date-write-iso-only.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 day it names and found by it, beside a
+ * `Date`.
+ *
+ * Measured on the base through REST over this driver: `"2026/07/15"`,
+ * `"07/15/2026"`, `"15 July 2026"` and `"2026-7-15"` were each a 201 read back
+ * verbatim — a non-day that compares as text beside real days. The engine
+ * refuses them now; the REST door over SQL is
+ * `packages/rest/src/data-date-write-iso-only.test.ts`.
+ */
+
+import { beforeAll, describe, expect, it } from 'vitest';
+import { InMemoryDriver } from './memory-driver.js';
+
+const OBJECT = 'ledger_date_20481';
+const FIELDS = { placed_on: { type: 'date' } };
+
+/** Each spelling the write door admits, and a `Date` — every one names 2026-07-15. */
+const ADMITTED: ReadonlyArray<readonly [string, unknown]> = [
+  ['bare', '2026-07-15'],
+  ['iso', '2026-07-15T10:00:00Z'],
+  ['naive', '2026-07-15 10:00'],
+  ['blank', ' 2026-07-15'],
+  ['date', new Date(Date.UTC(2026, 6, 15, 10))],
+];
+
+describe('[#20481] every date spelling the write door admits is stored as its day', () => {
+  let driver: InMemoryDriver;
+
+  beforeAll(async () => {
+    driver = new InMemoryDriver({});
+    await driver.connect();
+    await driver.syncSchema(OBJECT, { name: OBJECT, fields: FIELDS });
+    for (const [id, placed_on] of ADMITTED) await driver.create(OBJECT, { id, placed_on });
+    await driver.create(OBJECT, { id: 'before', placed_on: '2026-07-14' });
+  });
+
+  it('reads each one back as 2026-07-15', async () => {
+    for (const [id] of ADMITTED) {
+      expect((await driver.findOne(OBJECT, { where: { id } }))?.placed_on, id).toBe('2026-07-15');
+    }
+  });
+
+  it('finds each one by the day, and orders it after 2026-07-14', async () => {
+    const ids = async (where: Record<string, unknown>) =>
+      (await driver.find(OBJECT, { where })).map((r) => r.id as string).sort();
+    const all = ADMITTED.map(([id]) => id).sort();
+    expect(await ids({ placed_on: { $eq: '2026-07-15' } })).toEqual(all);
+    expect(await ids({ placed_on: { $gt: '2026-07-14' } })).toEqual(all);
+    expect(await ids({ placed_on: { $lt: '2026-07-15' } })).toEqual(['before']);
+  });
+});
@@ -0,0 +1,172 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * [#20481] A `date` string is written in its `YYYY-MM-DD` form or it is refused
+ * — `VALIDATION_FAILED` with the field's `invalid_date` code, on insert,
+ * update, a multi-row update and the dry-run `validate`, before any driver
+ * write.
+ *
+ * "Its `YYYY-MM-DD` form" is the `date` storage rule's own reading of a
+ * string (`@objectstack/core`'s `temporalStorageForm`): a leading `YYYY-MM-DD`
+ * after trimming, collapsed to that day. The write door asks the SAME
+ * predicate the temporal-comparand door asks (`isUninterpretableTemporalComparand`),
+ * so the two doors cannot disagree about which `date` strings the rule reads —
+ * the last block below holds them to that.
+ *
+ * Measured on the base (`0bbe4005e`) through REST, a create then a read-back,
+ * the process in America/New_York and PostgreSQL 16 at Asia/Shanghai with
+ * `DateStyle` `ISO, MDY`:
+ *
+ * | written to a `date` | memory | SQLite | PostgreSQL | now |
+ * |:--|:--|:--|:--|:--|
+ * | `"2026/07/15"`, `"07/15/2026"`, `"15 July 2026"`, `"2026-7-15"`, `"2026.07.15"`, `"July 15, 2026"` | 201, read back verbatim | 201, read back verbatim | 201, `"2026-07-15"` (its `DateStyle` reading) | 400 |
+ * | `"07/08/2026"` | 201, verbatim | 201, verbatim | 201, `"2026-07-08"` (August 7 under DMY) | 400 |
+ * | `"+002026-07-15"` | 201, verbatim | 201, verbatim | 500 | 400 |
+ * | `"2026-07-15T10:00:00Z"`, `"2026-07-15 10:00"`, `" 2026-07-15"`, `"2026-07-15"` | 201, `"2026-07-15"` | 201, `"2026-07-15"` | 201, `"2026-07-15"` | unchanged |
+ * | `"20260715"`, `"15/07/2026"` (no `Date.parse` reading) | 400 | 400 | 400 | unchanged |
+ * | an epoch-millisecond number | 400 | 400 | 400 | unchanged |
+ * | a `Date` | 201, its UTC day | 201, its UTC day | 201, its UTC day | unchanged |
+ *
+ * No other spelling is canonicalised, on purpose: `07/08/2026` names two days,
+ * and a guess stores the wrong one silently. The REST door over real drivers is
+ * `packages/rest/src/data-date-write-iso-only.test.ts`; this file's driver
+ * records writes and stores nothing, because the refusal sits in front of
+ * every driver.
+ */
+
+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 },
+  },
+};
+
+/** `Date.parse`-readable, no leading `YYYY-MM-DD` — each a 201 stored verbatim on memory and SQLite at the base. */
+const REFUSED: readonly string[] = [
+  '2026/07/15',
+  '07/15/2026',
+  '07/08/2026',
+  '15 July 2026',
+  'July 15, 2026',
+  '2026-7-15',
+  '2026.07.15',
+  '+002026-07-15',
+];
+
+/** Refused at the base already — kept refused. */
+const STILL_REFUSED: ReadonlyArray<readonly [string, unknown]> = [
+  ['no Date.parse reading', '20260715'],
+  ['a day-first spelling Date.parse cannot read', '15/07/2026'],
+  ['a leading day shape with no reading', '2026-13-45'],
+  ['a {placeholder}', '{today}'],
+  ['an epoch-millisecond number', Date.UTC(2026, 6, 15)],
+];
+
+/** A leading `YYYY-MM-DD` — the rule collapses each to `2026-07-15`, and a `Date` keeps its UTC day. */
+const ACCEPTED: ReadonlyArray<readonly [string, unknown]> = [
+  ['a bare day', '2026-07-15'],
+  ['an ISO instant', '2026-07-15T10:00:00Z'],
+  ['a zone-naive wall clock', '2026-07-15 10:00'],
+  ['a leading blank', ' 2026-07-15'],
+  ['a Date', new Date(Date.UTC(2026, 6, 15, 10))],
+];
+
+/** A driver that records every read and write, and answers none. */
+function makeRecordingDriver() {
+  const reads: unknown[] = [];
+  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(_o: string, ast: unknown) { reads.push(ast); return []; },
+    async findOne(_o: string, ast: unknown) { reads.push(ast); return { id: 'r1' }; },
+    async count(_o: string, ast: unknown) { reads.push(ast); return 0; },
+    async aggregate(_o: string, ast: unknown) { reads.push(ast); 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, reads, 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 = (value: unknown) => (value instanceof Date ? `Date ${value.toISOString()}` : JSON.stringify(value));
+
+describe('[#20481] the write door — a date string is written in its YYYY-MM-DD form, or it is VALIDATION_FAILED before any write', () => {
+  let engine: ObjectQL;
+  let reads: unknown[];
+  let writes: Record<string, unknown>[];
+
+  beforeEach(async () => {
+    const rec = makeRecordingDriver();
+    reads = rec.reads;
+    writes = rec.writes;
+    engine = new ObjectQL();
+    engine.registerDriver(rec.driver, true);
+    await engine.init();
+    engine.registry.registerObject(ledger, 'test');
+  });
+
+  const doors = (value: unknown) => [
+    ['insert', () => engine.insert('ledger', { id: 'n1', customer_id: 'c1', placed_on: value })],
+    ['update', () => engine.update('ledger', { id: 'r1', placed_on: value })],
+    ['multi-row update', () => engine.update('ledger', { placed_on: value }, { where: { customer_id: 'c1' }, multi: true })],
+  ] as const;
+
+  it('refuses every other spelling on insert, update and a multi-row update, with the field and invalid_date — and writes nothing', async () => {
+    for (const value of [...REFUSED, ...STILL_REFUSED.map(([, v]) => v)]) {
+      for (const [door, call] of doors(value)) {
+        const err = await refusalOf(call());
+        expect(err, `${door}, ${labelOf(value)}`).not.toBeNull();
+        expect(err!.code, `${door}, ${labelOf(value)}`).toBe('VALIDATION_FAILED');
+        expect(err!.fields, `${door}, ${labelOf(value)}`).toEqual([expect.objectContaining({ field: 'placed_on', code: 'invalid_date' })]);
+      }
+    }
+    expect(writes, 'no write — every refusal precedes the driver').toHaveLength(0);
+  });
+
+  it('the dry-run validate predicts each refusal — and each accepted value as valid', async () => {
+    for (const value of [...REFUSED, ...STILL_REFUSED.map(([, v]) => v)]) {
+      const verdict = await engine.validate('ledger', { placed_on: value });
+      expect(verdict.valid, labelOf(value)).toBe(false);
+      expect(verdict.results[0]!.errors, labelOf(value)).toEqual([expect.objectContaining({ field: 'placed_on', code: 'invalid_date' })]);
+    }
+    for (const [name, value] of ACCEPTED) {
+      expect((await engine.validate('ledger', { placed_on: value })).valid, name).toBe(true);
+    }
+  });
+
+  it('accepts a leading YYYY-MM-DD and a Date on every door — the POSITIVE CONTROL', async () => {
+    for (const [name, value] of ACCEPTED) {
+      for (const [door, call] of doors(value)) {
+        const before = writes.length;
+        await expect(call(), `${door}, ${name}`).resolves.toBeDefined();
+        expect(writes.length, `${door}, ${name} reached the driver`).toBe(before + 1);
+      }
+    }
+  });
+
+  it('one reading at both doors: a date string is refused as a written value exactly when it is refused as a comparand', async () => {
+    const strings = [...REFUSED, ...ACCEPTED.map(([, v]) => v).filter((v): v is string => typeof v === 'string')];
+    for (const value of strings) {
+      const written = (await engine.validate('ledger', { placed_on: value })).valid;
+      const err = await refusalOf(engine.find('ledger', { where: { placed_on: { $gte: value } } }));
+      if (err) expect(err, `where ${JSON.stringify(value)}`).toMatchObject({ code: 'INVALID_FILTER', status: 400 });
+      expect({ written, compared: err === null }, JSON.stringify(value)).toEqual({ written: !REFUSED.includes(value), compared: !REFUSED.includes(value) });
+    }
+    expect(reads, 'a read for each accepted comparand, none for a refused one').toHaveLength(strings.length - REFUSED.length);
+  });
+});
@@ -54,7 +54,8 @@
  *  - format         email / url / phone   (lightweight RFC-aware regex)
  *  - select / multiselect: value must appear in `options`
  *  - boolean / toggle: must coerce to boolean
- *  - date / datetime: must be ISO-parsable, naming a year from 0001 to 9999
+ *  - date / datetime: must be ISO-parsable, naming a year from 0001 to 9999;
+ *                   a `date` string also carries a leading `YYYY-MM-DD` (#20481)
  *
  * System-injected fields (`id`, `created_at`, `created_by`,
  * `updated_at`, `updated_by`, and provenance-flagged `system`/`readonly`
@@ -85,7 +86,7 @@ import {
   parseNumericString,
 } from '@objectstack/spec/data';
 import type { FieldErrorCode } from '@objectstack/spec/api';
-import { isOutsideTemporalYearRange } from '@objectstack/core';
+import { isOutsideTemporalYearRange, isUninterpretableTemporalComparand } from '@objectstack/core';
 import { isValueDomainMember, type ValueDomain } from '@objectstack/spec/shared';
 import {
   renderValidationMessage,
@@ -1220,7 +1221,29 @@ function validateOne(
     // 201 on memory and SQLite) and PostgreSQL refused it with a 500; year 0
     // is a 500 on PostgreSQL on both kinds. Same code and words as any other
     // value that is not a valid date.
-    if (readable && !isOutsideTemporalYearRange(value, t)) return null;
+    //
+    // [#20481] …and a `date` STRING is one the `date` storage rule reads: a
+    // leading `YYYY-MM-DD` (after trimming), which `temporalStorageForm`
+    // collapses to that day. The rule hands every other string back unchanged,
+    // so `"2026/07/15"`, `"07/15/2026"`, `"15 July 2026"` or `"2026-7-15"` —
+    // each `Date.parse`-readable — was stored verbatim on memory and SQLite, a
+    // non-day that sorts and compares as text beside real days, while
+    // PostgreSQL read it by its `DateStyle` (`07/08/2026` is July 8 under
+    // MDY and August 7 under DMY). No other spelling is canonicalised, on
+    // purpose: `07/08/2026` names two days, and a guess stores the wrong one
+    // silently. The question is asked of `@objectstack/core`'s
+    // `isUninterpretableTemporalComparand` — the temporal-comparand door's
+    // reading of the same rule, never a second copy of it here — so every
+    // `date` string that door refuses as a comparand is refused as a written
+    // value too; the `Date.parse` check above still applies on top of it
+    // (`2026-13-45` has a leading day shape and no reading). Its two
+    // comparand-only exemptions never reach here: a blank is missing before
+    // this arm, and a `{placeholder}` is not `Date.parse`-readable. A `Date`
+    // is not a string and keeps its UTC calendar day; a `datetime` is
+    // untouched.
+    const readsAsDay =
+      t !== 'date' || typeof value !== 'string' || !isUninterpretableTemporalComparand('date', value);
+    if (readable && readsAsDay && !isOutsideTemporalYearRange(value, t)) return null;
     // Same wire code, two sentences: "a valid date" vs "a valid datetime".
     return fail('invalid_date', { type: t }, t === 'datetime' ? 'invalid_datetime' : 'invalid_date');
   }