@@ -24,6 +24,6 @@ These refusals run after the walker's own (an unknown operator, a malformed refe
 
 Not refused, but answering differently:
 
-- **A `Date` bound is compared as an instant.** `{ opened_at: { $gt: new Date('2026-02-01') } }` against the ISO text a `datetime` column holds counted no row: JS compared the `Date` with the string by coercion. `$ne` and `$nin` counted every row, and a `$between` of two `Date`s counted every row. The same bound in a `where` counted 4 of 6 on both drivers. The comparison now reads the pair through `@objectstack/spec/data`'s `utcInstantMs`, the lift `@objectstack/formula`'s evaluator applies, whenever one side is a `Date` and both sides denote an instant. Every `datetime` row and a UTC-midnight `Date` on a `date` field now count what the same bound counts in a `where`. `having` shares this comparison, so a `Date` bound in `having` keeps the groups its ISO spelling keeps on a `datetime` column; on a `date`-class column (`min` / `max` of a `date` field) a UTC-midnight `Date` follows the calendar-day reading a `where` gives (`{ $gte: new Date('2026-02-01') }` keeps the group whose max is `2026-02-01`, and so does `$eq`), which the ISO-instant text, compared as text, did not. A `Date` is not JSON, so this reaches in-process callers only. Two readings still differ from a `where`, because the per-row comparison holds no declaration: a `Date` carrying a time of day against a `date` field, which a `where` reads as that UTC calendar day, and a `Date` against a `time` field, which is not an instant and is left as before.
+- **A `Date` bound is compared as an instant.** `{ opened_at: { $gt: new Date('2026-02-01') } }` against the ISO text a `datetime` column holds counted no row: JS compared the `Date` with the string by coercion. `$ne` and `$nin` counted every row, and a `$between` of two `Date`s counted every row. The same bound in a `where` counted 4 of 6 on both drivers. The comparison now reads the pair through `@objectstack/spec/data`'s `utcInstantMs`, the lift `@objectstack/formula`'s evaluator applies, whenever one side is a `Date` and both sides denote an instant. Every `datetime` row and a UTC-midnight `Date` on a `date` field now count what the same bound counts in a `where`. `having` shares this comparison, so a `Date` bound in `having` keeps the groups its ISO spelling keeps on a `datetime` column; on a `date`-class column (`min` / `max` of a `date` field) a UTC-midnight `Date` follows the calendar-day reading a `where` gives (`{ $gte: new Date('2026-02-01') }` keeps the group whose max is `2026-02-01`, and so does `$eq`), which the ISO-instant text, compared as text, did not. A `Date` is not JSON, so this reaches in-process callers only. Two readings still differed from a `where` in this change alone, because the per-row comparison held no declaration (#20176 closes both in the same release, reading every temporal comparand at this position by the column's storage rule): a `Date` carrying a time of day against a `date` field, which a `where` reads as that UTC calendar day, and a `Date` against a `time` field, which is not an instant and is left as before.
 
 Not changed, measured identical before and after on both drivers: every `where`, `groupBy` and `having` answer outside the `Date` shapes above, and a per-aggregation filter that uses implicit equality, ordering bounds, `$in`, `$between`, `$or`, `{}`, a `{ $field }` between two declared numeric fields, `addDays` between two `date` or two `datetime` fields (literal or read from a numeric column), and a reference to `created_at` or `id`.
@@ -0,0 +1,35 @@
+---
+"@objectstack/core": minor
+"@objectstack/objectql": minor
+"@objectstack/driver-sql": patch
+"@objectstack/driver-memory": patch
+---
+
+fix(objectql,core): a per-aggregation `filter` and `having` on `engine.aggregate` read a temporal comparand by the column's storage rule, the rule `where` already applies — one function, `temporalStorageForm`, now exported by `@objectstack/core` and shared by both drivers (#20176)
+
+A per-aggregation `filter` (`aggregations[i].filter`) and `having` are evaluated by the engine itself, over the rows (or aggregated rows) a driver returns. Both compared a temporal comparand exactly as written, while the same condition as a `where` is put into the column's storage form by the driver first. So they counted differently. Measured through `engine.aggregate` and through `POST /data/:object/query`, on `driver-memory` and `driver-sql`, over six rows:
+
+| in `aggregations[i].filter` (or `having`) | before | now, and the `where` twin |
+|:--|:--|:--|
+| an ISO instant on a `date` field, `{ placed_on: { $gte: '2026-02-01T00:00:00.000Z' } }` | 1 | 3 |
+| the same instant under `$eq` | 0 | 2 |
+| a bare day as the upper bound of a `datetime`, `{ opened_at: { $lte: '2026-02-01' } }`, or as a `$between` max | 2 | 3 |
+| an epoch-millisecond bound on a `datetime` | 0 | 3 |
+| a `Date` carrying a time of day on a `date` field, `$gte` / `$lt` / `$eq` (in-process only) | 1 / 5 / 0 | 3 / 3 / 2 |
+| a `Date` on a `time` field (in-process only) | 0 | 3 |
+| `having` on `max` of a `date` field with an ISO-instant bound | kept one group | keeps the two groups whose day is on or after it |
+
+The same holds for `$ne`, `$in` / `$nin` members, `$between` endpoints, implicit equality, an offset instant (`'…T18:00:00+08:00'`), an epoch-millisecond string, a zone-naive `'2026-02-01T10:00'`, and a short wall clock (`'11:00'`) or an ISO instant on a `time` field. On a `having` column, the class comes from the query, as the `addDays` rule already reads it: `min` / `max` take the class of the field they read, a `groupBy` projection takes its field's, and a `day` date bucket is a `date`.
+
+What the rule does, now in one place:
+
+- A comparand, and the row's value, are put into the column's storage form: canonical UTC ISO text for `datetime`, `YYYY-MM-DD` for `date`, and `HH:MM:SS` (`.fff` only when non-zero) for `time`.
+- A bare `YYYY-MM-DD` used as the upper bound of a `datetime` (`$lte`, a `$between` max) means that whole day, as it does in a `where` (ADR-0053 D-D). On a `date` or `time` column it is not widened.
+- A value the rule cannot read is compared as written, and so is every non-temporal column, presence tests (`$exists`, `$null`), the text operators and a `{ $field }` reference.
+- An object whose declared fields the engine cannot see keeps the previous comparison.
+
+`@objectstack/core` exports the rule as `temporalStorageForm(value, kind)`, `kind` being `'datetime' | 'date' | 'time'`. `driver-sql` (`canonicalUtcDatetime`, `toDateOnly`, `canonicalTimeOfDay`) and `driver-memory` (`coerceTemporalValue`) each carried a copy of it; both now call it. The copies agreed on every shape measured when they were lifted, so no `where`, write or read answer of either driver changes. MySQL still binds a `datetime` in its own literal spelling.
+
+`@objectstack/objectql`'s `applyInMemoryAggregation(rows, ast, timezone?, fields?)` takes the object's declared field map as an optional fourth argument, and a per-aggregation `filter` reads a temporal comparand by the rule only when it is given. Called without it, the function answers as before.
+
+Not changed, measured identical before and after on both drivers: every `where` answer, every refusal a per-aggregation `filter` or `having` gives, and every per-aggregation `filter` and `having` cell whose column is not temporal.
@@ -97,6 +97,13 @@ export * from './utils/analytics-date-range-conformance.js';
 // on each other.
 export * from './utils/temporal-comparand.js';
 
+// [#20176] …and the storage FORM that column's rule puts a value in — the one
+// rule `driver-sql` and `driver-memory` apply to a `where` comparand (and on
+// write), and `@objectstack/objectql` applies to a per-aggregation `filter` and
+// `having`, which it evaluates itself. Here because the drivers and the engine
+// do not depend on each other, and each driver used to carry its own copy.
+export * from './utils/temporal-storage-form.js';
+
 // [#12350 / ADR-0126 §4] THE activation-ledger row contract, parameterized by
 // `metadata_type`. Same reason as the two entries above: its consumers —
 // `@objectstack/objectql` (packaged actions) and
 
@@ -41,9 +41,9 @@
  * ## Interpretability is defined by the DRIVERS' own totals, deliberately
  *
  * Each predicate below mirrors the total function that would receive the value
- * if the door let it through — `storageDatetimeValue` / `storageDateValue` /
- * `storageTimeValue` in `driver-memory`, and their `SqlDriver` twins. Those
- * functions are total on purpose: an input they cannot interpret is returned
+ * if the door let it through — `temporalStorageForm` (`temporal-storage-form.ts`,
+ * the one rule both drivers read since #20176; before it, a copy in each).
+ * That function is total on purpose: an input it cannot interpret is returned
  * UNCHANGED rather than becoming an invented instant. So "the driver would
  * return it unchanged" IS the definition of uninterpretable, and defining it
  * any other way would refuse comparands that work today.
@@ -87,7 +87,7 @@ export function temporalComparandKind(fieldType: unknown): TemporalComparandKind
 }
 
 /**
- * `storageDatetimeValue`'s reading, as a yes/no.
+ * `temporalStorageForm`'s `datetime` reading, as a yes/no.
  *
  * Mirrors it step for step: a bare integer in either sign is epoch
  * milliseconds; a bare `YYYY-MM-DD` is midnight UTC; a zone-naive
@@ -105,11 +105,11 @@ function readsAsInstant(s: string): boolean {
 }
 
 /**
- * `storageDateValue`'s reading of a STRING: its leading `YYYY-MM-DD`, and
+ * `temporalStorageForm`'s `date` reading of a STRING: its leading `YYYY-MM-DD`, and
  * nothing else.
  *
  * Narrower than {@link readsAsInstant} on purpose, because the rule it mirrors
- * is narrower: `storageDateValue` collapses a leading calendar day and returns
+ * is narrower: the `date` rule collapses a leading calendar day and returns
  * every other string untouched. `2026/07/15` is therefore uninterpretable for a
  * `date` column even though `Date.parse` reads it — today it survives to the
  * driver and compares as text against `YYYY-MM-DD` values, which is the silent
@@ -120,7 +120,7 @@ function readsAsCalendarDay(s: string): boolean {
 }
 
 /**
- * `storageTimeValue`'s reading: a bare wall clock whose components are in
+ * `temporalStorageForm`'s `time` reading: a bare wall clock whose components are in
  * range. Out-of-range (`25:00`) is uninterpretable — the rule it mirrors
  * returns such a value untouched rather than wrapping it.
  */
 
@@ -0,0 +1,89 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+//
+// [#20176] `temporalStorageForm` — the ONE storage rule a temporal comparand is
+// put in before it is compared: by `driver-sql` and `driver-memory` on `where`
+// (and on write), and by `@objectstack/objectql` on a per-aggregation `filter`
+// and `having`. Each driver carried a word-for-word copy until it was lifted
+// here; the drivers' own suites pin that their `where` coercion IS this
+// function (`memory-temporal-storage-form.test.ts`,
+// `sql-driver-temporal-storage-form.test.ts`). This file pins the rule itself.
+
+import { describe, it, expect } from 'vitest';
+import { temporalStorageForm } from './temporal-storage-form.js';
+
+describe('temporalStorageForm — datetime: canonical UTC ISO text', () => {
+  const cases: ReadonlyArray<readonly [string, unknown, unknown]> = [
+    ['a Date', new Date('2026-02-01T10:00:00.000Z'), '2026-02-01T10:00:00.000Z'],
+    ['epoch milliseconds', 1769940000000, '2026-02-01T10:00:00.000Z'],
+    ['an epoch-millisecond string, padded', ' 1769940000000 ', '2026-02-01T10:00:00.000Z'],
+    ['a negative epoch string', '-86400000', '1969-12-31T00:00:00.000Z'],
+    ['a bare day — midnight UTC, never the host zone', '2026-02-01', '2026-02-01T00:00:00.000Z'],
+    ['a zone-naive wall clock — read AS UTC', '2026-02-01 09:00', '2026-02-01T09:00:00.000Z'],
+    ['a zone-naive T spelling with a long fraction', '2026-02-01T09:00:00.123456', '2026-02-01T09:00:00.123Z'],
+    ['an ISO instant without milliseconds', '2026-02-01T10:00:00Z', '2026-02-01T10:00:00.000Z'],
+    ['an offset instant — re-spelled in Z', '2026-02-01T18:00:00+08:00', '2026-02-01T10:00:00.000Z'],
+  ];
+  for (const [name, input, expected] of cases) {
+    it(name, () => expect(temporalStorageForm(input, 'datetime')).toBe(expected));
+  }
+});
+
+describe('temporalStorageForm — date: the UTC calendar day', () => {
+  const cases: ReadonlyArray<readonly [string, unknown, unknown]> = [
+    ['an ISO instant — its leading day', '2026-02-01T00:00:00.000Z', '2026-02-01'],
+    ['a Date carrying a time of day — its UTC day', new Date('2026-02-01T23:30:00.000Z'), '2026-02-01'],
+    ['a bare day, padded', '  2026-02-01  ', '2026-02-01'],
+    ['a zone-naive timestamp', '2026-02-01 23:59', '2026-02-01'],
+  ];
+  for (const [name, input, expected] of cases) {
+    it(name, () => expect(temporalStorageForm(input, 'date')).toBe(expected));
+  }
+
+  it('epoch milliseconds are not a calendar day — returned as they came', () => {
+    expect(temporalStorageForm(1769940000000, 'date')).toBe(1769940000000);
+  });
+});
+
+describe('temporalStorageForm — time: the UTC wall clock, .fff only when non-zero', () => {
+  const cases: ReadonlyArray<readonly [string, unknown, unknown]> = [
+    ['a short wall clock', '09:00', '09:00:00'],
+    ['a zero-millisecond suffix is trimmed', '09:00:00.000', '09:00:00'],
+    ['a fraction is kept to milliseconds', '09:00:00.5', '09:00:00.500'],
+    ['a Date — its UTC time of day', new Date('2026-02-01T11:00:00.000Z'), '11:00:00'],
+    ['an ISO instant — its UTC time of day', '2026-02-01T11:00:00.250Z', '11:00:00.250'],
+    ['a bare day — its midnight', '2026-02-01', '00:00:00'],
+  ];
+  for (const [name, input, expected] of cases) {
+    it(name, () => expect(temporalStorageForm(input, 'time')).toBe(expected));
+  }
+});
+
+describe('temporalStorageForm — total: what the rule cannot read comes back unchanged', () => {
+  const invalid = new Date('nope');
+  const untouched: ReadonlyArray<readonly [string, unknown]> = [
+    ['null', null],
+    ['undefined', undefined],
+    ['the empty string', ''],
+    ['whitespace', '   '],
+    ['junk', 'not-a-date'],
+    ['a preset name', 'last_30_days'],
+    ['a placeholder', '{today}'],
+    ['a boolean', true],
+    ['an Invalid Date', invalid],
+    ['NaN', Number.NaN],
+  ];
+  for (const kind of ['datetime', 'date', 'time'] as const) {
+    for (const [name, input] of untouched) {
+      it(`${kind}: ${name}`, () => expect(temporalStorageForm(input, kind)).toBe(input));
+    }
+  }
+
+  it('time: an out-of-range wall clock is not wrapped', () => {
+    expect(temporalStorageForm('25:00', 'time')).toBe('25:00');
+  });
+
+  it('a list is NOT mapped — a caller comparing a list maps its members', () => {
+    const list = ['2026-02-01', '2026-02-02'];
+    expect(temporalStorageForm(list, 'datetime')).toBe(list);
+  });
+});