diff --git a/‎.changeset/20157-engine-judge-filter.md‎
Lines changed: 16 additions & 0 deletions b/‎.changeset/20157-engine-judge-filter.md‎
Lines changed: 16 additions & 0 deletions
diff --git a/‎packages/objectql/src/engine-judge-filter.test.ts‎
Lines changed: 327 additions & 0 deletions b/‎packages/objectql/src/engine-judge-filter.test.ts‎
Lines changed: 327 additions & 0 deletions
@@ -0,0 +1,16 @@
+---
+"@objectstack/spec": minor
+"@objectstack/objectql": minor
+---
+
+`IObjectQLEngine` gains an optional judge-only member, `judgeFilter(objectName, where, { operation?, context? })`, and `ObjectQL` implements it (#20157, #19995 ruling C). It answers "can this filter run against this object?" without running anything: `{ ok: true }`, or `{ ok: false, code, status, message }` with the same diagnostic execution would raise.
+
+- **The engine's own admission, not a copy.** The judge calls the two stage functions every verb that takes a `where` already runs, in their order. First the lowering doors: the shape gate, the list-comparand shape, the virtual-field and dotted-path refusals, the text operator over a non-text field, the uninterpretable temporal comparand and the comparand-type door. Then the filter-placeholder resolver. A new door on that pipeline is judged the day it lands.
+- **Nothing executes.** No driver is resolved or called, and no hook or middleware runs. The member is synchronous, so a door that needs I/O cannot join it without a contract change. Driver-level refusals and the predicates middleware composes later (RLS, sharing, tenant scope) are not judged.
+- **Placeholders resolve against `context`**, exactly as execution resolves them. A context placeholder the context cannot answer (`{current_user_id}` with no user) is refused with `FILTER_TOKEN_UNRESOLVED`, never resolved to `null`.
+- **`operation`** (default `'find'`) names the verb the caller will run, so the message carries that verb's prefix. The verdict is the same on every verb.
+- **The message is not redacted.** It names fields, operators and comparands. A caller judging a filter it must not disclose, such as a read-scope policy, withholds the message itself.
+
+Optional by the ruling. A caller probes for it (`typeof ql.judgeFilter === 'function'`) and keeps its current behaviour on an engine without it. Existing engine doubles and foreign engines need no change. Execution is unchanged for every CRUD caller: same diagnostics, same order.
+
+Clause-②: yes
@@ -0,0 +1,327 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * [#20157] `ObjectQL.judgeFilter`, the engine's judge-only filter admission
+ * (`IObjectQLEngine.judgeFilter`, #19995 ruling C).
+ *
+ * What each block pins:
+ *
+ * - **Per class.** For each class #19995 lists (a text operator over a
+ *   non-text field, an uninterpretable temporal comparand, an unknown filter
+ *   placeholder, a filter on a virtual field, a dotted path through a lookup),
+ *   the judge returns the door's diagnostic, AND execution raises the same one.
+ *   Same `code`, `status` and `message`, on every verb that takes a `where`,
+ *   with `operation` naming the verb.
+ * - **Ok.** A runnable filter returns `{ ok: true }`.
+ * - **Nothing executes.** A driver spy sees no call, no driver is resolved,
+ *   and no hook or middleware runs. Each has a positive control: execution
+ *   drives the same spy.
+ * - **Order.** A filter with two defects gets the diagnostic execution gives.
+ *   The door stage runs before the placeholder stage, and the doors inside it
+ *   keep their order.
+ * - **Placeholders.** They resolve against the supplied context. One the
+ *   context cannot answer is refused, never resolved to `null`.
+ *
+ * Every refusal assertion reads `code` and `status` (the ADR-0112 envelope),
+ * never a bare `toThrow()`.
+ */
+
+import { describe, it, expect, beforeEach, vi } from 'vitest';
+import type { EngineFilterJudgement, EngineFilterJudgementOptions } from '@objectstack/spec/contracts';
+import type { EngineQueryOptions } from '@objectstack/spec/data';
+import type { ExecutionContext } from '@objectstack/spec/kernel';
+import { ObjectQL } from './engine.js';
+
+/** The `where` type every verb (and the judge) accepts. */
+type Where = EngineQueryOptions['where'];
+
+const DEAL = 'judge_deal';
+const ACCOUNT = 'judge_account';
+
+const ACCOUNT_SCHEMA = {
+  name: ACCOUNT,
+  label: 'Judge account',
+  fields: {
+    id: { name: 'id', type: 'text' },
+    name: { name: 'name', type: 'text' },
+  },
+};
+
+const DEAL_SCHEMA = {
+  name: DEAL,
+  label: 'Judge deal',
+  fields: {
+    id: { name: 'id', type: 'text' },
+    title: { name: 'title', type: 'text' },
+    owner_id: { name: 'owner_id', type: 'text' },
+    amount: { name: 'amount', type: 'number' },
+    closes_on: { name: 'closes_on', type: 'date' },
+    // A virtual field: no driver materialises a column for it.
+    is_open: { name: 'is_open', type: 'formula', expression: '1', returnType: 'boolean' },
+    account: { name: 'account', type: 'lookup', reference: ACCOUNT },
+  },
+};
+
+type Verb = NonNullable<EngineFilterJudgementOptions['operation']>;
+const VERBS: readonly Verb[] = ['find', 'findOne', 'count', 'aggregate', 'update', 'delete'];
+
+/** Run `where` through one verb's EXECUTION on `object`. */
+function execute(engine: ObjectQL, verb: Verb, object: string, where: Where, context?: ExecutionContext) {
+  switch (verb) {
+    case 'find': return engine.find(object, { where }, { context });
+    case 'findOne': return engine.findOne(object, { where }, { context });
+    case 'count': return engine.count(object, { where }, { context });
+    case 'aggregate':
+      return engine.aggregate(object, { where, aggregations: [{ function: 'count', alias: 'n' }] }, { context });
+    case 'update': return engine.update(object, { title: 'x' }, { where, multi: true, context });
+    case 'delete': return engine.delete(object, { where, multi: true, context });
+  }
+}
+
+type Thrown = Error & { code?: string; status?: number };
+
+async function refusalOf(p: Promise<unknown>): Promise<Thrown | null> {
+  return p.then(() => null, (e: unknown) => e as Thrown);
+}
+
+/** A recording driver: every method call lands in `calls`, by method name. */
+function makeRecordingDriver() {
+  const calls: string[] = [];
+  const reads: Array<{ method: string; ast: any }> = [];
+  const record = <A extends unknown[], R>(method: string, impl: (...args: A) => R) =>
+    (...args: A): R => { calls.push(method); return impl(...args); };
+  const driver: any = {
+    name: 'judge-recording', version: '0.0.0', supports: {},
+    connect: record('connect', async () => {}),
+    disconnect: record('disconnect', async () => {}),
+    checkHealth: record('checkHealth', async () => true),
+    execute: record('execute', async () => null),
+    find: record('find', async (_o: string, ast: any) => { reads.push({ method: 'find', ast }); return []; }),
+    findOne: record('findOne', async (_o: string, ast: any) => { reads.push({ method: 'findOne', ast }); return null; }),
+    count: record('count', async (_o: string, ast: any) => { reads.push({ method: 'count', ast }); return 0; }),
+    aggregate: record('aggregate', async (_o: string, ast: any) => { reads.push({ method: 'aggregate', ast }); return []; }),
+    create: record('create', async (_o: string, d: any) => d),
+    update: record('update', async (_o: string, id: any, d: any) => ({ id, ...d })),
+    updateMany: record('updateMany', async () => 0),
+    delete: record('delete', async () => true),
+    deleteMany: record('deleteMany', async () => 0),
+    bulkCreate: record('bulkCreate', async (_o: string, rows: any[]) => rows),
+    beginTransaction: record('beginTransaction', async () => ({})),
+    commit: record('commit', async () => {}),
+    rollback: record('rollback', async () => {}),
+  };
+  return { driver, calls, reads };
+}
+
+/**
+ * The five classes the ruling names, each with the envelope its door raises.
+ * `where` is a factory so no case can edit a filter another case judges.
+ */
+const CLASSES: ReadonlyArray<{ name: string; where: () => Where; code: string; status: number; mentions: string }> = [
+  {
+    name: 'a text operator over a non-text field',
+    where: () => ({ amount: { $contains: '5' } }),
+    code: 'INVALID_FILTER', status: 400, mentions: "'amount'",
+  },
+  {
+    name: 'an uninterpretable temporal comparand',
+    where: () => ({ closes_on: { $gt: 'not-a-date' } }),
+    code: 'INVALID_FILTER', status: 400, mentions: "'closes_on'",
+  },
+  {
+    name: 'an unknown filter placeholder',
+    where: () => ({ owner_id: '{bogus_token}' }),
+    code: 'FILTER_TOKEN_UNKNOWN', status: 400, mentions: '{bogus_token}',
+  },
+  {
+    name: 'a filter on a virtual field',
+    where: () => ({ is_open: true }),
+    code: 'INVALID_FIELD', status: 400, mentions: "'is_open'",
+  },
+  {
+    name: 'a dotted path through a lookup',
+    where: () => ({ 'account.name': 'Acme' }),
+    code: 'INVALID_FIELD', status: 400, mentions: "'account.name'",
+  },
+];
+
+function refused(verdict: EngineFilterJudgement): Extract<EngineFilterJudgement, { ok: false }> {
+  if (verdict.ok) throw new Error(`expected a refusal, the judge answered ok`);
+  return verdict;
+}
+
+describe('[#20157] ObjectQL.judgeFilter: judge a where without executing it', () => {
+  let engine: ObjectQL;
+  let calls: string[];
+  let reads: Array<{ method: string; ast: any }>;
+
+  beforeEach(async () => {
+    const rec = makeRecordingDriver();
+    calls = rec.calls;
+    reads = rec.reads;
+    engine = new ObjectQL();
+    engine.registerDriver(rec.driver, true);
+    await engine.init();
+    engine.registry.registerObject(ACCOUNT_SCHEMA as any, 'test');
+    engine.registry.registerObject(DEAL_SCHEMA as any, 'test');
+    // Boot traffic (connect, schema sync) is not the judge's; start clean.
+    calls.length = 0;
+    reads.length = 0;
+  });
+
+  describe('per class: the judge returns the diagnostic execution raises', () => {
+    for (const c of CLASSES) {
+      for (const verb of VERBS) {
+        it(`${c.name}, on ${verb}`, async () => {
+          const verdict = refused(engine.judgeFilter(DEAL, c.where(), { operation: verb }));
+          expect(calls).toEqual([]);
+
+          const thrown = await refusalOf(execute(engine, verb, DEAL, c.where()));
+          expect(thrown).not.toBeNull();
+          // The envelope, on both sides.
+          expect({ code: thrown!.code, status: thrown!.status }).toEqual({ code: c.code, status: c.status });
+          expect({ code: verdict.code, status: verdict.status }).toEqual({ code: c.code, status: c.status });
+          // The same diagnostic, byte for byte, including the verb prefix.
+          expect(verdict.message).toBe(thrown!.message);
+          expect(verdict.message).toContain(c.mentions);
+        });
+      }
+    }
+
+    it('the default operation is find', () => {
+      const bare = refused(engine.judgeFilter(DEAL, { amount: { $contains: '5' } }));
+      const asFind = refused(engine.judgeFilter(DEAL, { amount: { $contains: '5' } }, { operation: 'find' }));
+      expect(bare).toEqual(asFind);
+      expect(bare.message.startsWith(`find('${DEAL}')`)).toBe(true);
+    });
+
+    it('the filter-array sugar is judged through the same lowering execution runs', async () => {
+      // Input-only sugar: off the `where` type on purpose, as a caller holding
+      // a `FilterArray` passes it.
+      const where = [['amount', 'contains', '5']] as unknown as Where;
+      const verdict = refused(engine.judgeFilter(DEAL, where));
+      const thrown = await refusalOf(engine.find(DEAL, { where }));
+      expect({ code: verdict.code, status: verdict.status }).toEqual({ code: 'INVALID_FILTER', status: 400 });
+      expect({ code: thrown!.code, status: thrown!.status }).toEqual({ code: 'INVALID_FILTER', status: 400 });
+      expect(verdict.message).toBe(thrown!.message);
+    });
+
+    it('a where that is not a filter object gets the shape gate\'s diagnostic', async () => {
+      // Off-contract on purpose: the shape gate is what refuses it.
+      const where = 'status = open' as unknown as Where;
+      const verdict = refused(engine.judgeFilter(DEAL, where));
+      const thrown = await refusalOf(engine.find(DEAL, { where }));
+      expect({ code: verdict.code, status: verdict.status }).toEqual({ code: 'INVALID_FILTER', status: 400 });
+      expect(verdict.message).toBe(thrown!.message);
+    });
+  });
+
+  describe('a runnable filter', () => {
+    it('returns ok, and execution admits it and reaches the driver', async () => {
+      const where = { title: 'Acme', amount: { $gt: 5 }, closes_on: { $gte: '{30_days_ago}' } };
+      expect(engine.judgeFilter(DEAL, where)).toEqual({ ok: true });
+      expect(calls).toEqual([]);
+
+      // Positive control: the same filter executes, so the spy is live.
+      await engine.find(DEAL, { where });
+      expect(calls).toContain('find');
+    });
+
+    it('an absent, null or empty where is ok', () => {
+      expect(engine.judgeFilter(DEAL, undefined)).toEqual({ ok: true });
+      expect(engine.judgeFilter(DEAL, null as unknown as Where)).toEqual({ ok: true });
+      expect(engine.judgeFilter(DEAL, {})).toEqual({ ok: true });
+      expect(engine.judgeFilter(DEAL, [] as unknown as Where)).toEqual({ ok: true });
+    });
+
+    it('leaves the caller\'s filter untouched', () => {
+      const where = { owner_id: '{current_user_id}', closes_on: { $gte: '{30_days_ago}' } };
+      const before = JSON.stringify(where);
+      expect(engine.judgeFilter(DEAL, where, { context: { userId: 'u_1' } })).toEqual({ ok: true });
+      expect(JSON.stringify(where)).toBe(before);
+    });
+  });
+
+  describe('nothing executes', () => {
+    it('no driver method is called and no driver is resolved, for a refusal or an ok', async () => {
+      const getDriver = vi.spyOn(engine as any, 'getDriver');
+      for (const c of CLASSES) engine.judgeFilter(DEAL, c.where());
+      engine.judgeFilter(DEAL, { title: 'Acme' });
+      expect(calls).toEqual([]);
+      expect(getDriver).not.toHaveBeenCalled();
+
+      // Positive control: execution resolves the driver through the same spy.
+      await engine.find(DEAL, { where: { title: 'Acme' } });
+      expect(getDriver).toHaveBeenCalled();
+    });
+
+    it('no hook and no middleware runs', async () => {
+      const hook = vi.fn();
+      const middleware = vi.fn(async (_opCtx: unknown, next: () => Promise<void>) => { await next(); });
+      engine.registerHook('beforeFind', hook, { object: DEAL });
+      engine.registerMiddleware(middleware);
+
+      engine.judgeFilter(DEAL, { title: 'Acme' });
+      engine.judgeFilter(DEAL, { is_open: true });
+      expect(hook).not.toHaveBeenCalled();
+      expect(middleware).not.toHaveBeenCalled();
+
+      // Positive control: execution runs both.
+      await engine.find(DEAL, { where: { title: 'Acme' } });
+      expect(hook).toHaveBeenCalled();
+      expect(middleware).toHaveBeenCalled();
+    });
+  });
+
+  describe('order: the diagnostic execution gives when a filter has two defects', () => {
+    it('the door stage runs before the placeholder stage', async () => {
+      const where = (): Where => ({ owner_id: '{bogus_token}', amount: { $contains: '5' } });
+      const verdict = refused(engine.judgeFilter(DEAL, where()));
+      const thrown = await refusalOf(engine.find(DEAL, { where: where() }));
+      expect(verdict.code).toBe('INVALID_FILTER');
+      expect({ code: thrown!.code, status: thrown!.status }).toEqual({ code: 'INVALID_FILTER', status: 400 });
+      expect(verdict.message).toBe(thrown!.message);
+    });
+
+    it('inside the door stage, the materializable door answers before the text-operator door', async () => {
+      const where = (): Where => ({ amount: { $contains: '5' }, is_open: true });
+      const verdict = refused(engine.judgeFilter(DEAL, where()));
+      const thrown = await refusalOf(engine.find(DEAL, { where: where() }));
+      expect(verdict.code).toBe('INVALID_FIELD');
+      expect({ code: thrown!.code, status: thrown!.status }).toEqual({ code: 'INVALID_FIELD', status: 400 });
+      expect(verdict.message).toBe(thrown!.message);
+    });
+  });
+
+  describe('placeholders resolve against the supplied context, never to null', () => {
+    it('a context placeholder with no context is refused, as execution refuses it', async () => {
+      const where = { owner_id: '{current_user_id}' };
+      const verdict = refused(engine.judgeFilter(DEAL, where));
+      const thrown = await refusalOf(engine.find(DEAL, { where }));
+      expect({ code: verdict.code, status: verdict.status }).toEqual({ code: 'FILTER_TOKEN_UNRESOLVED', status: 400 });
+      expect({ code: thrown!.code, status: thrown!.status }).toEqual({ code: 'FILTER_TOKEN_UNRESOLVED', status: 400 });
+      expect(verdict.message).toBe(thrown!.message);
+    });
+
+    it('the same placeholder with the context execution would get is ok, and execution sends the resolved value', async () => {
+      const where = { owner_id: '{current_user_id}' };
+      expect(engine.judgeFilter(DEAL, where, { context: { userId: 'u_1' } })).toEqual({ ok: true });
+      await engine.find(DEAL, { where }, { context: { userId: 'u_1' } });
+      expect(reads.at(-1)?.ast.where).toEqual({ owner_id: 'u_1' });
+    });
+  });
+
+  describe('an object the registry does not know', () => {
+    it('the field-map doors answer nothing and the schema-free doors still judge, as at execution', async () => {
+      // A virtual-field verdict needs the field map; with none, it is ok.
+      expect(engine.judgeFilter('judge_unregistered', { is_open: true })).toEqual({ ok: true });
+      // The list-comparand shape gate needs no field map.
+      const where = (): Where => ({ status: { $in: 'open' } });
+      const verdict = refused(engine.judgeFilter('judge_unregistered', where()));
+      const thrown = await refusalOf(engine.find('judge_unregistered', { where: where() }));
+      expect({ code: verdict.code, status: verdict.status }).toEqual({ code: 'INVALID_FILTER', status: 400 });
+      expect({ code: thrown!.code, status: thrown!.status }).toEqual({ code: 'INVALID_FILTER', status: 400 });
+      expect(verdict.message).toBe(thrown!.message);
+    });
+  });
+});