@@ -0,0 +1,18 @@
+---
+'@objectstack/objectql': patch
+---
+
+fix(objectql)!: the in-process engine refuses a search-field override that names no field, as the Data API doors and the shared declarations do (#27732)
+
+Clause-②: no (narrowing) — the in-process engine (`find`, `findOne`, `count`, `aggregate`) refuses a `searchFields` or object-form `search.fields` that names no field (an empty list, or a comma string with no name in it), which it read as absent before. The doors already refuse it (#27484) and `QuerySchema.searchFields` / `FullTextSearchSchema.fields` declare the refusal (#27683). Nothing is widened.
+Metadata-protocol: none
+
+<!-- adr-0087: not-required (no-migration-prescription) No key of any schema is added, removed, renamed or re-shaped, and no export or type changes: an engine option value the shared declarations already refuse is now refused in process too. The refusal is the doors' VALIDATION_ERROR / 400, so there is nothing for a migration to rewrite and no tombstone. -->
+
+**BREAKING** accept-set narrowing at the engine's search override (`@objectstack/objectql`).
+
+- **Before.** `engine.find(obj, { search: 'acme', searchFields: [] })`, the same on `findOne` / `count` / `aggregate`, and `search: { query: 'acme', fields: [] }` scanned the object's whole default search set: an empty override read as no override. The caller wrote the key to narrow and was not told.
+- **Now.** Each is refused `400 VALIDATION_ERROR` (`param: 'searchFields'` or `'search.fields'`) before any driver read, whether or not a search term rides along, and for a system-context caller too. The message carries the declaration's own words ("Name at least one field, or leave the key out to search the default search fields"), and `mapDataError` serves it the status and code the REST door serves.
+- **Unchanged.** An absent (or `null`) override searches the default set. A named override narrows as before, and a name outside the searchable set is still intersected away in process (refused at the doors).
+
+**The remedy.** Leave the key out to search the default fields, or name at least one field.
@@ -1194,7 +1194,9 @@ the tolerant intersection, but not a search with nothing to scan: when no
 `searchableFields` entry names a stored field and the auto-default finds none
 (`internal: true` fields never count), the engine itself refuses a non-blank `search`
 with `400 INVALID_FIELD` (`param: 'search'`) on `find`, `findOne`, `count` and
-`aggregate` alike, rather than answering every row. Multiple whitespace-separated terms are AND-ed and
+`aggregate` alike, rather than answering every row. An override that names no field (`searchFields: []`,
+`search.fields: []`, or a comma string with no name in it) is refused there too, `400 VALIDATION_ERROR`, as
+at the ingress: leave the key out to search the default set. Multiple whitespace-separated terms are AND-ed and
 fields are OR-ed. Case sensitivity comes from the operator the expansion emits, not
 from the expansion: it emits `$icontains`, which ignores **ASCII case** by the
 rule in [Case Sensitivity](#case-sensitivity) above. So a user typing `acme` does
 
@@ -0,0 +1,223 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * [#27732] The in-process engine refuses a search-field override that names no
+ * field, as the Data API doors (#27484) and the shared declarations (#27683)
+ * do.
+ *
+ * `searchFields` and the object-form `search.fields` narrow which columns a
+ * `search` scans; absent means "scan the object's default search fields". The
+ * door refuses a value naming no field with `400 VALIDATION_ERROR`
+ * (`assertSearchFieldsAreSearchable`, `@objectstack/metadata-protocol`), and
+ * `QuerySchema.searchFields` / `FullTextSearchSchema.fields` refuse it too. The
+ * engine never parses its options with those schemas, and `resolveSearchFields`
+ * read an empty override as absent, so `find` / `findOne` / `count` /
+ * `aggregate` scanned the whole default set: a caller who wrote the override
+ * meant to narrow, and got the widest search instead, untold.
+ *
+ * Driven against a REAL {@link ObjectQL} engine over a driver double that
+ * evaluates `$or` / `$icontains` and records each read, so "refused before any
+ * driver read" is measured rather than assumed. `harbour` hits `name` on two
+ * rows and `city` on a third, so a narrowing is observable.
+ */
+
+import { describe, it, expect, beforeEach } from 'vitest';
+import { ObjectStackProtocolImplementation } from '@objectstack/metadata-protocol';
+import { QuerySchema, FullTextSearchSchema } from '@objectstack/spec/data';
+import type { EngineQueryOptions, EngineCountOptions, EngineAggregateOptions } from '@objectstack/spec/data';
+import { mapDataError } from '@objectstack/types';
+import { ObjectQL } from './engine.js';
+
+const account = {
+  name: 'acct_27732',
+  label: 'Account',
+  fields: {
+    id: { name: 'id', label: 'ID', type: 'text' as const, primaryKey: true },
+    name: { name: 'name', label: 'Name', type: 'text' as const },
+    city: { name: 'city', label: 'City', type: 'text' as const },
+    region: { name: 'region', label: 'Region', type: 'text' as const },
+  },
+};
+
+const ROWS: ReadonlyArray<Record<string, unknown>> = [
+  { id: 'a1', name: 'Harbour Freight', city: 'Boston', region: 'east' },
+  { id: 'a2', name: 'Harbour Lights', city: 'Seattle', region: 'west' },
+  { id: 'a3', name: 'Northgate Mills', city: 'Harbourton', region: 'east' },
+  { id: 'a4', name: 'Riverside Co', city: 'Portland', region: 'west' },
+];
+
+/** The shared declarations' own refusal words, read off the published schemas. */
+const declaredRefusal = (): string => {
+  const parsed = (QuerySchema as any).shape.searchFields.safeParse([]);
+  expect(parsed.success).toBe(false);
+  const nested = FullTextSearchSchema.shape.fields.safeParse([]);
+  expect(nested.success).toBe(false);
+  expect(nested.error!.issues[0].message).toBe(parsed.error!.issues[0].message);
+  return parsed.error!.issues[0].message;
+};
+
+function matches(row: Record<string, unknown>, where: unknown): boolean {
+  if (!where || typeof where !== 'object') return true;
+  for (const [k, v] of Object.entries(where as Record<string, unknown>)) {
+    if (k === '$and') { if (!(v as unknown[]).every((w) => matches(row, w))) return false; continue; }
+    if (k === '$or') { if (!(v as unknown[]).some((w) => matches(row, w))) return false; continue; }
+    if (k.startsWith('$')) throw new Error(`driver double does not implement the '${k}' combinator`);
+    if (v && typeof v === 'object' && '$icontains' in (v as any)) {
+      if (!String(row[k] ?? '').toLowerCase().includes(String((v as any).$icontains).toLowerCase())) return false;
+      continue;
+    }
+    const expected = v && typeof v === 'object' && '$eq' in (v as any) ? (v as any).$eq : v;
+    if (row[k] !== expected) return false;
+  }
+  return true;
+}
+
+function makeDriver() {
+  const reads: Array<{ via: string; where: unknown }> = [];
+  const driver: any = {
+    name: 'memory',
+    version: '0.0.0',
+    supports: {},
+    async connect() {}, async disconnect() {}, async checkHealth() { return true; }, async execute() { return null; },
+    async find(_o: string, ast: any) {
+      reads.push({ via: 'find', where: ast?.where });
+      const matched = ROWS.filter((r) => matches(r, ast?.where));
+      const page = typeof ast?.limit === 'number' ? matched.slice(0, ast.limit) : matched;
+      return page.map((r) => ({ ...r }));
+    },
+    async findOne(_o: string, ast: any) {
+      reads.push({ via: 'findOne', where: ast?.where });
+      const hit = ROWS.find((r) => matches(r, ast?.where));
+      return hit ? { ...hit } : null;
+    },
+    async count(_o: string, ast: any) {
+      reads.push({ via: 'count', where: ast?.where });
+      return ROWS.filter((r) => matches(r, ast?.where)).length;
+    },
+    async create(_o: string, d: any) { return d; },
+    async update(_o: string, _id: string, d: any) { return d; },
+    async delete() { return true; },
+    async bulkCreate(_o: string, r: any[]) { return r; },
+    async bulkUpdate() { return []; }, async bulkDelete() {},
+    async beginTransaction() { return { commit: async () => {}, rollback: async () => {} }; },
+    async commit() {}, async rollback() {},
+  };
+  return { driver, reads };
+}
+
+/** The refusal as the REST door would answer it: `mapDataError`'s status and code. */
+async function wireAnswer(read: Promise<unknown>) {
+  const err = await read.then(
+    () => { throw new Error('expected a refusal, got an answer'); },
+    (e: unknown) => e,
+  );
+  const mapped = mapDataError(err);
+  return { status: mapped.status, code: mapped.body.code, message: (err as Error).message, param: (err as any).param };
+}
+
+const COUNT = [{ function: 'count' as const, alias: 'n' }];
+
+type Verb = 'find' | 'findOne' | 'count' | 'aggregate';
+const VERBS: readonly Verb[] = ['find', 'findOne', 'count', 'aggregate'];
+
+/**
+ * Run one verb with the search keys in `bag`. Deliberately off-contract: the
+ * bags carry the comma-string and `null` spellings the engine-side declaration
+ * does not admit, as the wire path hands them over.
+ */
+function run(engine: ObjectQL, verb: Verb, bag: Record<string, unknown>): Promise<unknown> {
+  switch (verb) {
+    case 'find': return engine.find(account.name, bag as unknown as EngineQueryOptions);
+    case 'findOne': return engine.findOne(account.name, bag as unknown as EngineQueryOptions);
+    case 'count': return engine.count(account.name, bag as unknown as EngineCountOptions);
+    case 'aggregate': return engine.aggregate(account.name, { groupBy: ['region'], aggregations: COUNT, ...bag } as unknown as EngineAggregateOptions);
+  }
+}
+
+/** The ids a verb's answer covers, so a narrowing is read off the result. */
+async function answered(engine: ObjectQL, verb: Verb, bag: Record<string, unknown>): Promise<unknown> {
+  const out: any = await run(engine, verb, bag);
+  if (verb === 'find') return (out as any[]).map((r) => r.id).sort();
+  if (verb === 'findOne') return out?.id ?? null;
+  if (verb === 'count') return out;
+  return Object.fromEntries((out as any[]).map((r) => [r.region, r.n]));
+}
+
+/** What each verb answers for `harbour` over the DEFAULT set, and narrowed to `name`. */
+const DEFAULT_ANSWER: Record<Verb, unknown> = {
+  find: ['a1', 'a2', 'a3'], findOne: 'a1', count: 3, aggregate: { east: 2, west: 1 },
+};
+const NAME_ONLY_ANSWER: Record<Verb, unknown> = {
+  find: ['a1', 'a2'], findOne: 'a1', count: 2, aggregate: { east: 1, west: 1 },
+};
+
+describe('[#27732] the in-process engine refuses a search-field override naming no field', () => {
+  let engine: ObjectQL;
+  let reads: Array<{ via: string; where: unknown }>;
+
+  beforeEach(async () => {
+    engine = new ObjectQL();
+    const made = makeDriver();
+    reads = made.reads;
+    engine.registerDriver(made.driver, true);
+    await engine.init();
+    engine.registry.registerObject(account, 'test-package');
+  });
+
+  describe.each(VERBS)('%s', (verb) => {
+    it('searchFields: [] is refused 400 VALIDATION_ERROR in the declarations\' words, before any driver read', async () => {
+      const answer = await wireAnswer(run(engine, verb, { search: 'harbour', searchFields: [] }));
+      expect(answer).toMatchObject({ status: 400, code: 'VALIDATION_ERROR', param: 'searchFields' });
+      expect(answer.message).toContain(declaredRefusal());
+      expect(reads).toEqual([]);
+    });
+
+    it('search: { query, fields: [] } is refused the same way (item 1, the search.fields coupling)', async () => {
+      const answer = await wireAnswer(run(engine, verb, { search: { query: 'harbour', fields: [] } }));
+      expect(answer).toMatchObject({ status: 400, code: 'VALIDATION_ERROR', param: 'search.fields' });
+      expect(answer.message).toContain(declaredRefusal());
+      expect(reads).toEqual([]);
+    });
+
+    it('a comma string naming no field (the GET transport form) is refused the same way', async () => {
+      const answer = await wireAnswer(run(engine, verb, { search: 'harbour', searchFields: ' , ' }));
+      expect(answer).toMatchObject({ status: 400, code: 'VALIDATION_ERROR', param: 'searchFields' });
+      expect(reads).toEqual([]);
+    });
+
+    it('CONTROL: a named override still narrows', async () => {
+      expect(await answered(engine, verb, { search: 'harbour', searchFields: ['name'] })).toEqual(NAME_ONLY_ANSWER[verb]);
+      expect(await answered(engine, verb, { search: { query: 'harbour', fields: ['name'] } })).toEqual(NAME_ONLY_ANSWER[verb]);
+    });
+
+    it('CONTROL: an absent override still searches the default set', async () => {
+      expect(await answered(engine, verb, { search: 'harbour' })).toEqual(DEFAULT_ANSWER[verb]);
+      expect(await answered(engine, verb, { search: { query: 'harbour' } })).toEqual(DEFAULT_ANSWER[verb]);
+    });
+  });
+
+  it('an empty override is refused whether or not a search term rode along, as the door judges it', async () => {
+    const answer = await wireAnswer(engine.find(account.name, { searchFields: [] }));
+    expect(answer).toMatchObject({ status: 400, code: 'VALIDATION_ERROR', param: 'searchFields' });
+    expect(reads).toEqual([]);
+  });
+
+  it('a system-context read is refused too: the rule is about the shape, not the caller', async () => {
+    const answer = await wireAnswer(engine.find(account.name, { search: 'harbour', searchFields: [], context: { isSystem: true } }));
+    expect(answer).toMatchObject({ status: 400, code: 'VALIDATION_ERROR' });
+    expect(reads).toEqual([]);
+  });
+
+  it('the REST door answers the same status and code for the same override', async () => {
+    const protocol = new ObjectStackProtocolImplementation(engine);
+    const door = await wireAnswer(protocol.findData({ object: account.name, query: { search: 'harbour', searchFields: '' } as any }));
+    const inProcess = await wireAnswer(engine.find(account.name, { search: 'harbour', searchFields: [] }));
+    expect({ status: inProcess.status, code: inProcess.code }).toEqual({ status: door.status, code: door.code });
+    expect(door).toMatchObject({ status: 400, code: 'VALIDATION_ERROR' });
+    expect(reads).toEqual([]);
+  });
+
+  it('CONTROL: a null override is a withdrawal and searches the default set', async () => {
+    expect(await answered(engine, 'find', { search: 'harbour', searchFields: null })).toEqual(DEFAULT_ANSWER.find);
+  });
+});
@@ -138,7 +138,10 @@ describe('[#24284] a search over an empty resolved search set is refused', () =>
     });
 
     it('an explicit searchFields narrowing does not rescue it — the allowed set is empty, so the fallback is too', async () => {
-        for (const searchFields of [['title'], ['book'], ['nope'], []]) {
+        // [#27732] An empty override is no longer a narrowing to rescue: it
+        // names no field, and is refused before the expansion
+        // (engine-empty-search-fields-refusal.test.ts).
+        for (const searchFields of [['title'], ['book'], ['nope']]) {
             const err: any = await engine.find('lib_loan', { search: 'Dune', searchFields }).then(() => null, (e) => e);
             expect(err, `searchFields ${JSON.stringify(searchFields)}`).toMatchObject(REFUSAL);
         }
 
@@ -5,7 +5,7 @@ import { QueryAST, QueryInput, HookContext, ServiceObject } from '@objectstack/s
 // [commit 74155c735] The defaulting node schema `fillQueryAstDefaults` runs author input
 // through — the declared `.default()` stays in `packages/spec`, the engine
 // only invokes it.
-import { SortNodeSchema } from '@objectstack/spec/data';
+import { SortNodeSchema, FullTextSearchSchema } from '@objectstack/spec/data';
 import {
   EngineQueryOptions,
   DataEngineInsertOptions,
@@ -735,6 +735,40 @@ const ENGINE_AGGREGATE_OPTION_KEYS: ReadonlySet<string> = new Set([
   'search', 'searchFields',
 ]);
 
+/**
+ * [#27732] A search-field override — `searchFields`, or the object-form
+ * `search.fields` — that names no field is refused `400 VALIDATION_ERROR`:
+ * an empty list, or a comma string with no name in it (the `GET` door's
+ * transport spelling, which reaches the engine as sent). Absent (or `null`)
+ * still searches the object's default search fields.
+ *
+ * `resolveSearchFields` reads an empty override as absent, so the search
+ * widened to the whole default set: the caller wrote the key to narrow and was
+ * not told. The door refuses this set (`assertSearchFieldsAreSearchable`,
+ * #27484) and `QuerySchema.searchFields` / `FullTextSearchSchema.fields`
+ * declare the same refusal (#27683); the words are read off that declaration
+ * rather than copied, and the status and code are the door's, so
+ * `mapDataError` answers an in-process caller and a REST caller alike. Any
+ * other value is left to the expansion's existing tolerance.
+ */
+function refuseSearchOverrideNamingNoField(object: string, requested: unknown, param: string): void {
+  const names = typeof requested === 'string'
+    ? requested.split(',').map((s) => s.trim()).filter(Boolean)
+    : Array.isArray(requested) ? requested : undefined;
+  if (names === undefined || names.length > 0) return;
+  const declared = FullTextSearchSchema.shape.fields.safeParse([]).error?.issues[0]?.message;
+  const err: any = new Error(
+    `ObjectQL search on '${object}' names no field in '${param}': got ${JSON.stringify(requested)}. The query was not run: `
+    + "an empty search-field list was read as no narrowing, which scans the object's default search fields. "
+    + `${declared}.`,
+  );
+  err.status = 400;
+  err.code = 'VALIDATION_ERROR';
+  err.param = param;
+  err.object = object;
+  throw err;
+}
+
 /**
  * Rows per page for the autonumber seeding scan (#6249). This is a PAGE size,
  * not a cap: the walk pages until the scope is exhausted. The number is the one
@@ -13397,6 +13431,11 @@ export class ObjectQL implements IObjectQLEngine {
     // unknown option — rejected at the entry point, not silently dropped
     // (#4371).
     const raw = (ast as any).search;
+    // [#27732] An override naming no field is refused, never read as absent.
+    // Judged before the expansion and so before any driver read, whether or
+    // not a search term rode along, on both slots, as the door does.
+    refuseSearchOverrideNamingNoField(ast.object, (ast as any).searchFields, 'searchFields');
+    if (raw !== null && typeof raw === 'object') refuseSearchOverrideNamingNoField(ast.object, raw.fields, 'search.fields');
     if (raw != null && schema?.fields) {
       const requestedFields = (ast as any).searchFields
         ?? (typeof raw === 'object' ? raw?.fields : undefined);