@@ -0,0 +1,38 @@
+---
+'@object-ui/core': patch
+'@object-ui/plugin-grid': patch
+'@object-ui/plugin-list': patch
+---
+
+Fix: a grid grouped by a field it does not also show as a column no longer collapses
+every row into one `(empty)` group (objectui#7179).
+
+`$select` was built from the view's `columns` and nothing else, so a view declaring
+`grouping: { fields: [{ field: 'business_unit' }] }` on a field absent from its columns
+never asked the server for that field. It was `undefined` on every row by the time
+grouping ran, and the grouping label builder — correctly, for a genuinely empty value —
+answered `(empty)` for all of them. The result was one collapsible group holding every
+record, with no error, no warning and no empty state: a grid that looked like it grouped
+and did not, reading as "these records have no value for this field".
+
+The grouping fields are now unioned into the projection, at both places it is built —
+`ObjectGrid` when it fetches for itself, and `ListView` when it fetches and hands the
+rows down. Lookup grouping fields are unioned into `$expand` as well: a `select` that
+fetches a bare foreign key without populating it buckets by raw id instead of by name,
+which is a different wrong answer rather than a fix.
+
+Authors do not need to mirror a grouping field in `columns` any more. That was never
+required by `@objectstack/spec` — `grouping` is a sibling of `columns`, not a subset of
+it — and the neighbouring view kinds (kanban, gantt, timeline) already unioned their
+`groupByField` with no column needed. Refusing the configuration at author time was
+considered and rejected: it would make the grid the odd one out and reject working
+intent that the schema explicitly allows.
+
+The union is guarded, and the guard is as load-bearing as the fix. A `grouping.fields[]`
+entry carries a bare string that has never been through column validation, and some
+backends answer an unknown `$select` key with an empty result set rather than ignoring
+it. Unioned unguarded, a grouping field naming something the object does not declare
+would have turned this bug into a strictly worse one — no rows at all, equally silently.
+Grouping fields are therefore intersected with the object's declared fields and passed
+through the same field-level-security gate as columns and predicate operands before they
+reach the query.
@@ -98,6 +98,10 @@ export * from './utils/predicate-record.js';
 // The other half of a view's field appetite: the fields its PREDICATES read,
 // which the column-derived `$select` never asked the server for.
 export * from './utils/predicate-fields.js';
+// The THIRD source of a view's field appetite: the fields it GROUPS BY. The
+// spec's `grouping` block is a sibling of `columns`, not a subset, so a grid
+// may group by a field it never shows (objectui#7179).
+export * from './utils/grouping-fields.js';
 export * from './utils/normalize-list-view.js';
 // The single home for the VALUE fallback prettifier (a stored value becomes a
 // display string when nothing resolves it). `@object-ui/fields` and
 
@@ -0,0 +1,84 @@
+/**
+ * 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#7179 — the grouping-field harvester's own contract.
+ *
+ * The two renderer suites (`plugin-grid`'s `groupingProjection-7179` and
+ * `plugin-list`'s `ListView.groupingProjection-7179`) pin what reaches the
+ * QUERY. This pins the harvest itself, which is the half those two cannot
+ * fully reach: a malformed entry that crashes a consumer's own unrelated code
+ * before the projection is built is invisible to them, and the `null` case
+ * below is exactly that — `ObjectGrid`'s `groupValueFormatter` memo throws on
+ * it today, so the only place the harvester's handling of `null` is observable
+ * is here.
+ */
+import { describe, it, expect } from 'vitest';
+import { collectGroupingFieldRefs } from '../grouping-fields';
+
+describe('collectGroupingFieldRefs (objectui#7179)', () => {
+  it('harvests the field name from the spec shape', () => {
+    expect(
+      collectGroupingFieldRefs({ fields: [{ field: 'business_unit', order: 'asc', collapsed: false }] }),
+    ).toEqual(['business_unit']);
+  });
+
+  it('preserves first-seen order across a multi-level block', () => {
+    expect(
+      collectGroupingFieldRefs({ fields: [{ field: 'business_unit' }, { field: 'region' }] }),
+    ).toEqual(['business_unit', 'region']);
+  });
+
+  it('deduplicates a repeated field', () => {
+    expect(
+      collectGroupingFieldRefs({ fields: [{ field: 'region' }, { field: 'region' }] }),
+    ).toEqual(['region']);
+  });
+
+  it('trims surrounding whitespace so a padded name is not sent as an unknown key', () => {
+    expect(collectGroupingFieldRefs({ fields: [{ field: '  region  ' }] })).toEqual(['region']);
+  });
+
+  it.each([
+    ['undefined', undefined],
+    ['null', null],
+    ['an empty block', {}],
+    ['a non-array `fields`', { fields: 'business_unit' }],
+    ['an empty `fields`', { fields: [] }],
+  ])('harvests nothing from %s', (_label, input) => {
+    expect(collectGroupingFieldRefs(input)).toEqual([]);
+  });
+
+  it('contributes nothing for a NULL entry rather than throwing', () => {
+    // The shape no consumer survives today. The harvester must not be the
+    // thing that throws, so the crash stays attributable to its real owner.
+    expect(collectGroupingFieldRefs({ fields: [null, { field: 'region' }] })).toEqual(['region']);
+  });
+
+  it('contributes nothing for an entry with no `field`', () => {
+    expect(collectGroupingFieldRefs({ fields: [{}, { field: 'region' }] })).toEqual(['region']);
+  });
+
+  it('contributes nothing for a non-string `field`', () => {
+    expect(collectGroupingFieldRefs({ fields: [{ field: 42 }, { field: 'region' }] })).toEqual(['region']);
+  });
+
+  it('contributes nothing for an empty or whitespace-only `field`', () => {
+    expect(collectGroupingFieldRefs({ fields: [{ field: '' }, { field: '   ' }] })).toEqual([]);
+  });
+
+  it('REFUSES a bare string entry — the shorthand the spec does not accept', () => {
+    // `GroupingConfigSchema.fields` is an array of `$strict` OBJECTS. Reading a
+    // bare string anyway would be the lenient renderer-side alias AGENTS.md
+    // #0.1 forbids: it fossilizes a second de-facto contract instead of having
+    // the producer rejected at publish. It also could not work end to end —
+    // `useGroupedData` reads `f.field` off each entry, so a bare string groups
+    // by `undefined` no matter what the projection asks for.
+    expect(collectGroupingFieldRefs({ fields: ['business_unit'] })).toEqual([]);
+  });
+});
@@ -0,0 +1,79 @@
+/**
+ * ObjectUI
+ * Copyright (c) 2024-present ObjectStack Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+/**
+ * The THIRD half of a view's field appetite (objectui#7179).
+ *
+ * A list view projects what it DISPLAYS — `$select` is built from `columns`.
+ * `predicate-fields.ts` covers the fields a view's PREDICATES read. This covers
+ * the fields it GROUPS BY, which is a third, independent source of demand: the
+ * spec's `grouping` block is a sibling of `columns`, not a subset of it, so a
+ * view may legitimately group by a field it never shows.
+ *
+ * ## Why it needed a fix rather than a gate
+ *
+ * `GroupingConfigSchema` accepts `grouping` with no matching column, and the
+ * neighbouring view kinds (kanban / gantt / timeline) already union their
+ * `groupByField` into the projection with no column required. Grouping by a
+ * field you do not want on screen is an ordinary thing to want. Refusing it at
+ * author time would make the grid the odd one out and reject working intent.
+ *
+ * ## The failure this closes
+ *
+ * With the grouping field absent from `$select` the server never returns it,
+ * so `useGroupedData` reads `undefined` on every row and `buildSegmentLabel`
+ * answers `(empty)` for all of them: ONE group holding every record, with no
+ * error, no warning and no empty state. It reads as "these records have no
+ * value for this field" — a plausible, wrong, actionable conclusion about the
+ * data rather than a visible bug in the view.
+ *
+ * ## ⛔ THE RESULT IS CANDIDATES, NOT VERIFIED FIELDS — the caller MUST gate it
+ *
+ * `GroupingFieldSchema.field` is a bare `z.ZodString`. Nothing in the schema
+ * requires it to name a field the object declares, and the whole premise of
+ * this harvest is that it has NOT been through column validation. Some backends
+ * answer an unknown `$select` key with an EMPTY RESULT SET rather than ignoring
+ * it — the cloud multi-tenant runtime does exactly that — so a single unknown
+ * grouping field put in the projection unguarded silently zeroes the whole
+ * list. That would convert this card's bug (one `(empty)` group holding every
+ * row) into a strictly worse one (no rows at all, still silent).
+ *
+ * So every caller intersects this result with the object's declared fields —
+ * {@link isProjectableField}, or the caller's equivalent known-field set —
+ * exactly as {@link collectPredicateFieldRefs}'s callers do, and for the same
+ * measured reason. Callers additionally FLS-gate it: a grouping field names a
+ * field just as capable of being denied as a column is, and the projection is
+ * what goes on the wire (objectui#6898).
+ *
+ * @param grouping - The view's `grouping` block in any authored state
+ *   (`undefined`, malformed, or the spec shape). Anything that is not an entry
+ *   carrying a non-empty string `field` contributes nothing, so a malformed
+ *   block yields an empty harvest instead of a plausible wrong name.
+ * @returns Grouping field names in first-seen order, deduplicated.
+ */
+export function collectGroupingFieldRefs(grouping: unknown): string[] {
+  const fields = (grouping as { fields?: unknown } | null | undefined)?.fields;
+  if (!Array.isArray(fields)) return [];
+  const out: string[] = [];
+  const seen = new Set<string>();
+  for (const entry of fields) {
+    // The spec shape is `{ field, order, collapsed }`. A bare string is NOT
+    // accepted here even though it would be a natural shorthand: `grouping` is
+    // a `$strict` object schema in `@objectstack/spec`, so a bare string is
+    // off-spec metadata, and reading it anyway would be exactly the lenient
+    // renderer-side alias AGENTS.md #0.1 forbids — it fossilizes a second
+    // de-facto contract instead of having the producer rejected at publish.
+    const name = (entry as { field?: unknown } | null | undefined)?.field;
+    if (typeof name !== 'string') continue;
+    const trimmed = name.trim();
+    if (!trimmed || seen.has(trimmed)) continue;
+    seen.add(trimmed);
+    out.push(trimmed);
+  }
+  return out;
+}