feat(driver-mongodb): lower dateGranularity groupBy to $dateToString bucket labels, and publish supports.queryDateGranularity (#7580)

`driver-mongodb` published no `queryDateGranularity`, so `engine.aggregate`
bucketed every granularity in memory: correct answers, but the whole result set
shipped to the client before the rollup. #7550 refused a bucketed node at the
builder rather than implement or silently drop it, and sized the native lowering
as a card of its own. This is that card.

The bucket LABELS are the engine's own spellings, because the engine picks
between the pushed-down and in-memory paths per query and a drill-down can cross
that seam. All five declared granularities are advertised — `week` included,
where driver-sql on SQLite cannot, because `$dateToString` has both halves of
the ISO-8601 week date (`%G`/`%V`).

No `$dateTrunc`: it answers a truncated DATE that still needs formatting, raises
the server floor to MongoDB 5.0, and adds binSize/startOfWeek semantics this
fleet cannot observe. `$dateToString` answers the label directly out of one
operator, and fewer unobserved operators is the whole argument.

All three ADR-0053 storage forms are served through one total expression:
`$convert … onError/onNull: null` mirrors `bucketDateValue`'s totality, so a
BSON Date, `YYYY-MM-DD` text, `HH:MM:SS` text, null, missing and unparseable
junk all bucket the way the engine buckets them.

The capability record and the builder's refusal read ONE constant, so an
advertised granularity the builder would refuse cannot exist — the failure worse
than advertising nothing, since the engine stops bucketing in memory on the
strength of the bit.

Parity is proven by running the SAME rows through the real
`applyInMemoryAggregation` and through the emitted pipeline. driver-mongodb can
depend on objectql where driver-sql cannot (objectql depends on no driver), so
this is a devDependency rather than the hand-copied `bucketDateValue` the three
SQL bucket suites carry, and the drift their `⚠️ Keep in sync` comments admit
they cannot detect does not exist here.

The strict in-process evaluator moved to `mongodb-pipeline-evaluator.testkit.ts`
so both suites share one reader; only the date operators were added. It models
the manual independently — its own ISO-8601 grammar, `%G`/`%V` from the standard
— so the two sides CAN disagree and the comparison means something.

⚠️ Nothing here has met a real mongod (#5517: proxy 403 on the binary). The
bound is written into the suite header, onto the published capability, and
beside the lowering.

Fixes #7580

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019QkW7hhVvhTxh4V9Wmnqdy

Author: claude

.changeset/mongodb-native-date-granularity.md

@@ -0,0 +1,50 @@
+---
+"@objectstack/driver-mongodb": patch
+---
+
+feat(driver-mongodb): bucket `dateGranularity` groupBy server-side, and publish `supports.queryDateGranularity` (#7580)
+
+`driver-mongodb` now lowers a `dateGranularity`-bearing `groupBy` into the
+aggregation pipeline and advertises the capability, so `engine.aggregate` pushes
+a bucketed aggregate down to MongoDB instead of fetching every matching row and
+bucketing it in JS.
+
+**Answers do not change — where the work happens does.** `MongoDBDriver.supports`
+published no `queryDateGranularity`, so the engine already bucketed every
+granularity in memory and the results were correct. What was missing was the
+index/server-side half: a year-over-year rollup shipped the whole result set to
+the client first. #7550 refused a bucketed node at the builder rather than
+implement or silently drop it; this replaces that refusal with the lowering it
+described.
+
+**All five granularities `DateGranularity` declares are advertised** — `day`,
+`week`, `month`, `quarter`, `year`. The bucket LABELS are the engine's own
+spellings (`'2024'`, `'2024-Q1'`, `'2024-01'`, `'2024-01-15'`, ISO `'2025-W01'`),
+because the engine picks between the pushed-down and in-memory paths per query
+and a drill-down can cross that seam. `week: true` where `driver-sql` on SQLite
+carries `week: false`: MongoDB's `$dateToString` has both halves of the ISO-8601
+week date (`%G`/`%V`), SQLite has neither.
+
+**All three ADR-0053 storage forms are served.** This driver stores `datetime` as
+a BSON `Date` but `date` and `time` as timezone-naive TEXT, so the lowering reads
+the instant through `$convert … onError/onNull: null` — total, exactly like the
+in-memory `bucketDateValue`, which puts null, missing and unparseable values in
+one empty bucket. A `Field.time` column is a wall clock and not an instant: both
+paths agree it has no bucket, rather than one of them inventing a day.
+
+**Timezones are unchanged and stay engine-side.** `engine.aggregate` forces the
+in-memory path for any non-UTC reference zone (ADR-0053 Phase 2 D2) and the AST
+it hands a driver carries no `timezone`, so this bucketing is UTC by
+construction.
+
+The #7550 refusal is kept for a granularity outside the advertised record —
+`NOT_IMPLEMENTED` / 501 in the ADR-0112 envelope, now naming what *is* bucketed
+here — and it reads the same constant the capability record publishes, so the
+two cannot drift.
+
+⚠️ **Bound, stated because a green suite reads as more than it is.** Parity with
+the engine's labels is proven through a strict in-process pipeline evaluator, not
+against a live mongod: this environment cannot fetch a mongod binary (#5517). The
+`$convert` / `$dateToString` / `$concat` / `$switch` semantics the lowering stands
+on are documentation-derived. The bound is written into the suite header, onto
+the published capability, and beside the lowering.

packages/drivers/driver-mongodb/package.json

@@ -26,6 +26,7 @@
     "nanoid": "^6.0.0"
   },
   "devDependencies": {
+    "@objectstack/objectql": "workspace:*",
     "@types/node": "^26.1.2",
     "mongodb-memory-server": "^11.2.0",
     "typescript": "^6.0.3",

packages/drivers/driver-mongodb/src/index.ts

@@ -5,7 +5,11 @@ import { MongoDBDriver } from './mongodb-driver.js';
 export { MongoDBDriver };
 export type { MongoDBDriverConfig } from './mongodb-driver.js';
 export { translateFilter } from './mongodb-filter.js';
-export { buildAggregationPipeline, postProcessAggregation } from './mongodb-aggregation.js';
+export {
+  buildAggregationPipeline,
+  postProcessAggregation,
+  MONGODB_DATE_GRANULARITIES,
+} from './mongodb-aggregation.js';
 export type { AggregationInput } from './mongodb-aggregation.js';
 export {
   MongoDBMultiTenantUnsupportedError,