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+---
+'@object-ui/fields': minor
+---
+
+A `datetime` grid cell now honours the same authored `field.format` words a `date` cell already honoured (objectui#8853).
+
+`DateCellRenderer` and `DateTimeCellRenderer` are neighbours reading ONE authored key
+and handing it to two formatters with different vocabularies: `formatDate` honours
+`'short'` and `'relative'`, `formatDateTime`'s `options.style` honours `'compact'`
+alone. So `format: 'relative'` painted the relative face on a `date` column and the
+verbose absolute face on a `datetime` one — no error, no warning, no fallback.
+Measured end to end through a real `ObjectGrid` column before anything was changed:
+one object, one row, one instant (`2026-09-11T09:30:00.000Z`, clock pinned to
+`2026-09-09T12:00:00.000Z`, `en-US`), `format: 'relative'` authored on both fields,
+the grid's own body cells read
+
+    ["1Open", "Row One", "In 2 days", "Sep 11, 2026, 09:30 AM"]
+
+with the `date` column honouring the key and the `datetime` column beside it dropping
+it. After this change the same run reads `["1Open", "Row One", "In 2 days", "In 2
+days"]`.
+
+The cell now SELECTS a formatter instead of threading one, the way objectui#8352
+already ruled for `formatMeasureDate`'s datetime arm — the same defect class one
+surface over:
+
+- `'relative'` resolves through `formatRelativeDate`, the same function the `date`
+  cell reaches, so one calendar day reads the same phrase in either column.
+- `'short'` resolves to the dense face of this type, which for a `datetime` cell is
+  the compact face it already paints — the time of day is kept, and it stays
+  byte-identical to an unstyled cell.
+- every other string, `'compact'` and date patterns such as `'YYYY-MM-DD'` included,
+  falls to the default face exactly as before.
+
+**Behaviour change, spelled out.** Two authored spellings render differently than they
+did, and one of them loses a component:
+
+- `format: 'relative'` on a `datetime` field: was the verbose absolute face
+  (`Sep 11, 2026, 09:30 AM`), is now the relative phrase (`In 2 days`).
+- `format: 'short'` on a `datetime` field: was that same verbose face, is now the
+  compact face (`9/11/2026 9:30 am`).
+- ⚠️ **Beyond the ±7-day window a `'relative'` datetime now shows no time of day.**
+  `formatRelativeDate` falls back to an absolute DATE face out there, so
+  `2026-09-20T09:30:00.000Z` renders `Sep 20` where it rendered
+  `Sep 20, 2026, 09:30 AM` before. That window belongs to `formatRelativeDate` and is
+  inherited rather than re-decided at the call site — re-deciding it would put a
+  second copy of the convention in the renderer, which is objectui#4576. `'relative'`
+  is day-granular by construction (it shows no time inside the window either), and
+  any other fallback would make the two columns unequal again, which is the defect
+  being closed.
+
+Note what the delta is and is not: this renderer ignored both words outright before,
+so nothing was taken from a working feature — it starts honouring a request whose
+granularity is days. It reaches only a `datetime` field whose author actually wrote
+one of those two words. An unstyled `datetime` cell, an explicit `'compact'` one, an
+authored empty string, and any other spelling all render exactly as they did.
+
+No published signature moved. `formatDateTime(value, options?)` is unchanged and
+still ignores `'relative'` and `'short'` in its `options.style` key — threading the
+authored word into it would have honoured `'compact'`, the one word the `date` cell
+does NOT honour, while still ignoring both words it does, which is the defect
+inverted rather than closed. No spelling that rendered before is refused now; adding
+a refusal would be a breaking narrowing of a published metadata surface.
+
+`dueLike` is deliberately not threaded and is filed separately as objectui#8958: it
+is a different authored key whose affordance travels with red styling and a
+field-name heuristic, and acquiring a second key's behaviour while honouring the
+first would be an unruled change.
@@ -0,0 +1,261 @@
+/**
+ * ObjectUI
+ * Copyright (c) 2024-present ObjectStack Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+/**
+ * objectui#8853 — ONE authored `field.format`, one meaning, across the two
+ * neighbouring date cell renderers.
+ *
+ * ## What was measured, before anything was changed
+ *
+ * Driven end to end through a REAL `ObjectGrid` column (not inferred from a
+ * source read): one object with a `date` field and a `datetime` field, BOTH
+ * authored `format: 'relative'`, one row, one instant
+ * (`2026-09-11T09:30:00.000Z`), clock pinned to `2026-09-09T12:00:00.000Z`,
+ * `en-US`. The grid's own body cells came back as
+ *
+ *   ["1Open", "Row One", "In 2 days", "Sep 11, 2026, 09:30 AM"]
+ *                         ^ date       ^ datetime, same key, dropped
+ *
+ * and after the call-site mapping, as
+ *
+ *   ["1Open", "Row One", "In 2 days", "In 2 days"]
+ *
+ * The defect's whole signature is a SILENT drop — the runtime accepts the key,
+ * parses it, drops it, and renders something that still looks like a
+ * legitimate date — so a green suite proves nothing by itself. Every case
+ * below therefore asserts a rendered FACE, with controls that say what the
+ * probe would have shown had it been fooled.
+ *
+ * ## The controls, and why each one is here
+ *
+ * - **Positive control** — the `date` cell, in the SAME run, on the SAME
+ *   instant. It already honoured `'relative'`, so it is what "honoured" looks
+ *   like; without it, a datetime assertion could be measuring a broken clock
+ *   or a dead locale channel rather than the vocabulary.
+ * - **Negative control** — an OUT-OF-WINDOW value. `formatRelativeDate` falls
+ *   back to the absolute form beyond ±7 days, so out there `format:
+ *   'relative'` and no format at all render IDENTICALLY on the fully working
+ *   `date` cell. That is the trap objectui#8352's card recorded: a probe built
+ *   on an out-of-window value reports "identical" on a working path and on a
+ *   broken one alike. The pin below asserts that collapse explicitly, so the
+ *   in-window choice everywhere else is a measured decision rather than luck.
+ *
+ * ## Directions
+ *
+ * Reverting the call-site mapping in `DateTimeCellRenderer` turns the repro,
+ * the `'short'` face and the out-of-window datetime face RED, and leaves every
+ * control and regression pin GREEN — the controls measure surfaces this change
+ * does not touch, which is exactly why they can vouch for the run. Widening
+ * `formatDateTime`'s published signature instead (the refused route) turns the
+ * "published signature untouched" pins RED. Adding a refusal for a spelling
+ * that renders today turns the regression pins RED.
+ */
+import { describe, it, expect, vi, afterEach } from 'vitest';
+import React from 'react';
+import { render, cleanup } from '@testing-library/react';
+import '@testing-library/jest-dom';
+import { I18nProvider, LocalizationProvider } from '@object-ui/i18n';
+import { DateCellRenderer, DateTimeCellRenderer, formatDateTime, formatDateTimeCompactParts } from '../index';
+
+/** The pinned clock, and two values chosen on either side of the ±7-day window. */
+const CLOCK = '2026-09-09T12:00:00.000Z';
+/** +2 days: inside the window, so the relative face is a PHRASE and discriminates. */
+const IN_WINDOW = '2026-09-11T09:30:00.000Z';
+/** +11 days: outside it, where the relative face collapses onto the absolute one. */
+const OUT_OF_WINDOW = '2026-09-20T09:30:00.000Z';
+
+/** `en-US` plus one NON-US locale, the same pairing the #7443 pins use. */
+const LOCALES = ['en-US', 'zh', 'de-DE'];
+
+/**
+ * Same session harness as `datetime-compact-style-7443.test.tsx`: the tag is
+ * set as the TENANT locale because that is the channel objectui#4468 made
+ * every date branch read, and `persistLanguage={false}` keeps each case on its
+ * own language instead of inheriting the previous one's.
+ */
+function renderSession(locale: string, node: React.ReactElement) {
+  return render(
+    <I18nProvider
+      config={{ defaultLanguage: 'en', detectBrowserLanguage: false }}
+      persistLanguage={false}
+    >
+      <LocalizationProvider value={{ locale }}>{node}</LocalizationProvider>
+    </I18nProvider>,
+  );
+}
+
+/** Render one cell at the pinned clock and return its text, nothing retained. */
+function faceOf(node: React.ReactElement, locale = 'en-US'): string {
+  vi.useFakeTimers();
+  vi.setSystemTime(new Date(CLOCK));
+  try {
+    const { container } = renderSession(locale, node);
+    return container.textContent ?? '';
+  } finally {
+    cleanup();
+    vi.useRealTimers();
+  }
+}
+
+const dateCell = (value: string, format?: string) => (
+  <DateCellRenderer
+    value={value}
+    field={{ type: 'date', name: 'follow_up_on', ...(format === undefined ? {} : { format }) } as any}
+  />
+);
+
+const dateTimeCell = (value: string, format?: string) => (
+  <DateTimeCellRenderer
+    value={value}
+    field={{ type: 'datetime', name: 'follow_up_at', ...(format === undefined ? {} : { format }) } as any}
+  />
+);
+
+/** The compact face as the cell paints it — two spans, so no separating space. */
+function compactCellText(value: string, locale: string): string {
+  const parts = formatDateTimeCompactParts(value, { locale })!;
+  return `${parts.date}${parts.time}`;
+}
+
+afterEach(() => {
+  cleanup();
+  vi.useRealTimers();
+});
+
+describe('THE REPRO — `format: relative` means the same thing in both cells (#8853)', () => {
+  it('a datetime cell honours `relative`, and renders the phrase its date sibling renders', () => {
+    const dateFace = faceOf(dateCell(IN_WINDOW, 'relative'));
+    const dateTimeFace = faceOf(dateTimeCell(IN_WINDOW, 'relative'));
+
+    // The anchor, so a redesign that moved both sides together cannot pass.
+    expect(dateFace).toBe('In 2 days');
+    expect(dateTimeFace).toBe('In 2 days');
+    // The claim itself: ONE authored key, ONE meaning, across the two cells.
+    expect(dateTimeFace).toBe(dateFace);
+    // And what it used to be, named — not merely "something else".
+    expect(dateTimeFace).not.toBe('Sep 11, 2026, 09:30 AM');
+  });
+
+  it.each(LOCALES)('%s — the two cells agree in a non-US locale too', (locale) => {
+    expect(faceOf(dateTimeCell(IN_WINDOW, 'relative'), locale)).toBe(
+      faceOf(dateCell(IN_WINDOW, 'relative'), locale),
+    );
+  });
+
+  it('`short` reaches the dense face of THIS type — the time of day is kept', () => {
+    // objectui#8352 mapped `'short'` to the arm's own narrow face: `formatDate`'s
+    // `'short'` for a date, the compact datetime face for a datetime. Here that
+    // face is the one this cell already paints, so a measure tile and a grid
+    // cell showing the same instant agree.
+    expect(faceOf(dateTimeCell(IN_WINDOW, 'short'))).toBe(compactCellText(IN_WINDOW, 'en-US'));
+    expect(faceOf(dateTimeCell(IN_WINDOW, 'short'))).toBe('9/11/20269:30 am');
+    expect(faceOf(dateTimeCell(IN_WINDOW, 'short'))).not.toBe('Sep 11, 2026, 09:30 AM');
+  });
+
+  it('the relative face is painted in ONE span, not the compact two', () => {
+    vi.useFakeTimers();
+    vi.setSystemTime(new Date(CLOCK));
+    const { container } = renderSession('en-US', dateTimeCell(IN_WINDOW, 'relative'));
+    expect(container.querySelectorAll('span > span')).toHaveLength(0);
+    vi.useRealTimers();
+  });
+});
+
+describe('POSITIVE CONTROL — the date cell, unchanged, in the same run', () => {
+  it('still honours `relative` and `short`, and still defaults to relative', () => {
+    expect(faceOf(dateCell(IN_WINDOW, 'relative'))).toBe('In 2 days');
+    expect(faceOf(dateCell(IN_WINDOW, 'short'))).toBe("Sep 11, '26");
+    expect(faceOf(dateCell(IN_WINDOW, undefined))).toBe('In 2 days');
+  });
+
+  it("`compact` stays inert on a date cell — the vocabulary was widened on ONE side", () => {
+    // The reverse asymmetry the card names. Honouring it here would be a
+    // second, unruled change: `'compact'` falls to the date arm's default
+    // face, exactly as objectui#8352 declared for the measure path.
+    expect(faceOf(dateCell(IN_WINDOW, 'compact'))).toBe('Sep 11');
+    expect(faceOf(dateCell(IN_WINDOW, 'compact'))).toBe(faceOf(dateCell(IN_WINDOW, 'no-such-face')));
+  });
+});
+
+describe('NEGATIVE CONTROL — out of the ±7-day window the probe cannot discriminate', () => {
+  it('on the WORKING date cell, `relative` and no format render identically out there', () => {
+    // This is the trap. Had the cases above used this value, "identical"
+    // would have been the answer on a working path and a broken one alike.
+    const authored = faceOf(dateCell(OUT_OF_WINDOW, 'relative'));
+    const absent = faceOf(dateCell(OUT_OF_WINDOW, undefined));
+    expect(authored).toBe(absent);
+    expect(authored).toBe('Sep 20');
+  });
+
+  it('the in-window value DOES discriminate on that same cell — the probe has teeth', () => {
+    expect(faceOf(dateCell(IN_WINDOW, 'relative'))).not.toBe('Sep 11');
+  });
+
+  it('an out-of-window datetime renders the absolute DATE face — the declared cost', () => {
+    // ⚠️ The time of day is gone. `formatRelativeDate`'s out-of-window branch
+    // renders through `toLocaleDateString` and has no time component to add;
+    // that window belongs to that function and is INHERITED here rather than
+    // re-decided at this call site (objectui#4576). `'relative'` is day-granular
+    // by construction, so its degraded form is a day face — and nothing was
+    // taken from a working feature, since this cell ignored the word outright
+    // before. Pinned so the cost cannot drift silently in either direction.
+    expect(faceOf(dateTimeCell(OUT_OF_WINDOW, 'relative'))).toBe('Sep 20');
+    expect(faceOf(dateTimeCell(OUT_OF_WINDOW, 'relative'))).toBe(
+      faceOf(dateCell(OUT_OF_WINDOW, 'relative')),
+    );
+  });
+});
+
+describe('REGRESSION — every datetime cell that rendered before renders the same', () => {
+  it.each(LOCALES)('%s — no format is still the compact face', (locale) => {
+    expect(faceOf(dateTimeCell(IN_WINDOW, undefined), locale)).toBe(
+      compactCellText(IN_WINDOW, locale),
+    );
+  });
+
+  it('an explicit `compact` is still the compact face', () => {
+    expect(faceOf(dateTimeCell(IN_WINDOW, 'compact'))).toBe(compactCellText(IN_WINDOW, 'en-US'));
+  });
+
+  it('an authored EMPTY string is still the compact face, not the verbose one', () => {
+    // `||`, not `??` — the spelling objectui#7443 chose so an authored empty
+    // string stays on the compact face. The mapping above must not disturb it.
+    expect(faceOf(dateTimeCell(IN_WINDOW, ''))).toBe(compactCellText(IN_WINDOW, 'en-US'));
+  });
+
+  it('an unrecognised spelling still falls to the verbose default — no refusal was added', () => {
+    // ⛔ Rejecting a currently-accepted spelling would be a breaking narrowing
+    // of a published metadata surface. It renders, as it always did.
+    expect(faceOf(dateTimeCell(IN_WINDOW, 'default'))).toBe('Sep 11, 2026, 09:30 AM');
+    expect(faceOf(dateTimeCell(IN_WINDOW, 'YYYY-MM-DD'))).toBe('Sep 11, 2026, 09:30 AM');
+  });
+
+  it('an absent field is still tolerated, on the compact face', () => {
+    expect(faceOf(<DateTimeCellRenderer value={IN_WINDOW} field={undefined as any} />)).toBe(
+      compactCellText(IN_WINDOW, 'en-US'),
+    );
+  });
+});
+
+describe('the PUBLISHED signature was not moved — the mapping lives at the call site', () => {
+  it('formatDateTime still declares exactly two parameters', () => {
+    // `(value, options?)` is 2; the refused `(value, style?, options?)` is 3.
+    expect(formatDateTime.length).toBe(2);
+  });
+
+  it("formatDateTime's own vocabulary is untouched: it still ignores `relative` and `short`", () => {
+    // The function was NOT widened. It answers the verbose face for both
+    // words, and the CELL is what maps them — which is why this file and the
+    // function's own pins can disagree about `'relative'` without either being
+    // wrong.
+    const verbose = formatDateTime(IN_WINDOW, { locale: 'en-US' });
+    expect(formatDateTime(IN_WINDOW, { locale: 'en-US', style: 'relative' })).toBe(verbose);
+    expect(formatDateTime(IN_WINDOW, { locale: 'en-US', style: 'short' })).toBe(verbose);
+    expect(verbose).toBe('Sep 11, 2026, 09:30 AM');
+  });
+});