@@ -101,7 +101,8 @@ const CALLERS: Record<string, Classification> = {
     kind: 'not-a-door',
     reason: 'the provider\'s service registration: it binds the admission into the `security` service the plugin registers; it serves no rows',
   },
-  'packages/objectql/src/engine.ts': {
+  // [#25522 cut 15] The ReadableIds composition's admission ask, moved out of engine.ts.
+  'packages/objectql/src/engine-readable-ids-permission-formula.ts': {
     kind: 'not-a-door',
     reason:
       'the ReadableIds composition (ADR-0139 D2): it asks the admission of a PARENT object to compose the scope of a `$in` leaf '
 
@@ -0,0 +1,362 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * [#25522 cut 15] The `ReadableIds` composition, permission and formula
+ * resolution bodies of `ObjectQL`, moved out of `engine.ts`:
+ * `composeReadableIdsChain` (the chain of composed read scopes),
+ * `findUnservableControlledByParentMasters` (the boot screen over
+ * `controlled_by_parent` details), `readableIdsScopeOf` (the scope one leaf is
+ * composed with), `resolveOptionPermissions`, `permissionResolution`,
+ * `resolveFormulaPermissions` and `resolveDefaultPermissions` (an operation's
+ * one effective-permission resolution and its three consumers) and
+ * `reportFormulaFault` (a formula fault, said once per field).
+ *
+ * A MOVE, not a redesign. Each exported function below is the body of the
+ * `ObjectQL` method of the same name as it stood, re-indented one level and
+ * otherwise unedited. Each method's docblock stays on the method in
+ * `engine.ts`, which is still the contract.
+ *
+ * What stays in `engine.ts`: `composeReadableIdsAtBoundary` and
+ * `refuseUncomposableReadableIdsClasses` (ADR-0139 names them by path),
+ * `resolveReadableIdsSecurity` (it hands `this` on as a value),
+ * `resolveFormulaRelated` (its return type, `FormulaRelated`, is shared with
+ * module helpers that stay, and exporting it reorders the published declaration
+ * chunk), and the short ones that do not pay for a host
+ * (`uncomposableReadableIdsParent`, `serveFormulaField`, `formulaFaultSink`).
+ *
+ * ## How the moved bodies reach the class
+ *
+ * The shape #23050 set for `rest-server.ts`, applied per method as
+ * `engine-driver-options.ts` applies it. The class keeps all eight methods with
+ * name, modifiers, signature, docblock and position. Seven bodies become one
+ * literal of exactly the {@link ReadableIdsPermissionFormulaHost} members that
+ * method reads, plus a `.call`. The fields a body reads (`_registry`, `logger`,
+ * `_effectiveObjectPermissionsResolver`, `formulaFaultReported`) go as GETTERS,
+ * so each read happens when the body makes it, as it did; no moved body assigns
+ * a field. The methods they call go as late-bound closures over the instance,
+ * so a double or spy set on the engine is still the one a call reaches, and
+ * `composeReadableIdsChain`'s recursion re-enters through the method.
+ * `resolveOptionPermissions` reads no member of the class, so its method calls
+ * the function directly.
+ *
+ * ## Module helpers
+ *
+ * `READABLE_IDS_MAX_CHAIN_DEPTH` is read by `composeReadableIdsChain` alone, so
+ * it moved with it. Two helpers are read by these bodies AND by bodies that
+ * stay: `writeFailureLogMeta` (the write doors' failure logs) and
+ * `isExpressionDefault` (`applyFieldDefaults`). One home each: they stay
+ * declared in `engine.ts`, exported in place, and are imported here, never
+ * copied. The types these bodies share with bodies that stay
+ * (`PermissionResolution`, `FormulaPlanEntry`, `ReadableIdsSecurity`,
+ * `ReadableIdsChain`) are exported in place the same way and imported as types.
+ * Nothing re-exports any of them from the package entry, so the published
+ * surface does not move.
+ *
+ * That import is a run-time module cycle (`engine.ts` imports this module, this
+ * module imports `engine.ts`). Nothing here runs at module evaluation, only
+ * declarations, and `engine.ts` imports this module after every module this one
+ * imports, so the engine's evaluation order is what it was. The published build
+ * bundles both files into one, where the cycle does not exist.
+ */
+
+import { ReadableIds, RLS_DENY_FILTER, isControlledByParentMasterField, markFilterSubtreeProvenance } from '@objectstack/spec/data';
+import type { FilterCondition } from '@objectstack/spec/data';
+import type { ExecutionContext } from '@objectstack/spec/kernel';
+import { toEvalPermissions, type EvalError, type EvalPermissions } from '@objectstack/formula';
+import { collectComposableReadableIds, composeReadableIdsLeaves, describeReadableIdsLeaf, readableIdsRefusalError } from './filter-comparand-shape.js';
+import type { ComposableReadableIdsSite } from './filter-comparand-shape.js';
+import { optionVisibilityReadsPermissions, readsPermissionPredicate } from './validation/rule-validator.js';
+import { isExpressionDefault, writeFailureLogMeta } from './engine.js';
+import type { FormulaPlanEntry, PermissionResolution, ReadableIdsChain, ReadableIdsSecurity, UnservableControlledByParentMaster } from './engine.js';
+import type { ObjectQL } from './engine.js';
+
+/**
+ * The `ObjectQL` members the functions below read — every one of them, and no
+ * other; each function's `this` is the `Pick` of the members IT reads. Each is
+ * typed AS the class member (an indexed access on the class), so a change to a
+ * member's type on the class is a change here too, and naming a member the
+ * class does not have is a compile error. See the module header for which
+ * members are getters, and which one also has a setter.
+ */
+export interface ReadableIdsPermissionFormulaHost {
+  readonly _registry: ObjectQL['_registry'];
+  readonly logger: ObjectQL['logger'];
+  readonly _effectiveObjectPermissionsResolver: ObjectQL['_effectiveObjectPermissionsResolver'];
+  readonly formulaFaultReported: ObjectQL['formulaFaultReported'];
+  refuseUncomposableReadableIdsClasses: ObjectQL['refuseUncomposableReadableIdsClasses'];
+  readableIdsScopeOf: ObjectQL['readableIdsScopeOf'];
+  composeReadableIdsChain: ObjectQL['composeReadableIdsChain'];
+  uncomposableReadableIdsParent: ObjectQL['uncomposableReadableIdsParent'];
+  buildEvalUser: ObjectQL['buildEvalUser'];
+  defaultFieldEntries: ObjectQL['defaultFieldEntries'];
+}
+
+/**
+ * [ADR-0139 D6, as amended — the nested master chain] How deep a chain of
+ * composed scopes the engine composes: the scope answered for a leaf in the
+ * read's own `where` is one scope deep, the scope answered for a leaf inside
+ * it is two, and so on down a master-detail chain whose every master is
+ * itself `controlled_by_parent`. A chain deeper than this is refused by name.
+ *
+ * A COST ceiling, not a semantic rule, and the same cut as the
+ * `controlled_by_parent` derivation's (`CBP_MAX_CHAIN_DEPTH`,
+ * `packages/plugins/plugin-security`): a detail with seven derived masters
+ * above it composes, an eighth derived master is refused there and here.
+ * Every authored chain in this repository is one hop, the deepest any consumer
+ * has asked for is two, and 8 is four times that. Termination needs no bound —
+ * the chain refuses a parent already on its branch — so what this caps is the
+ * statement the driver compiles, one nested subquery per level. At the bound
+ * the read is REFUSED, loud (D5's envelope), ⛔ never composed partway and
+ * never answered "no restriction".
+ */
+const READABLE_IDS_MAX_CHAIN_DEPTH = 8;
+
+/** The body of `ObjectQL#composeReadableIdsChain`; the method's docblock there is its contract. */
+export async function composeReadableIdsChain<N>(
+  this: Pick<ReadableIdsPermissionFormulaHost, 'refuseUncomposableReadableIdsClasses' | 'readableIdsScopeOf' | 'composeReadableIdsChain'>,
+  chain: ReadableIdsChain,
+  node: N,
+  sites: readonly ComposableReadableIdsSite[],
+  ancestors: readonly string[],
+): Promise<N> {
+  const { object, operation } = chain;
+  const parents = this.refuseUncomposableReadableIdsClasses(object, operation, sites);
+  for (const parent of parents) {
+    if (chain.answers.has(parent)) continue;
+    const site = sites.find((s) => s.leaf.object === parent)!;
+    const branch = [object, ...ancestors, parent];
+    if (ancestors.includes(parent)) {
+      throw readableIdsRefusalError(
+        object,
+        `${operation}('${object}'): ${describeReadableIdsLeaf(site.at, site.leaf)}, inside the read scope of ` +
+        `'${ancestors[ancestors.length - 1]}', and the engine composes no such leaf: the chain of read scopes ` +
+        `${branch.join(' -> ')} returns to '${parent}', a cycle. The query was NOT run and no driver was asked. ` +
+        `A parent's read scope cannot be derived from its own readable ids; fix the read scope the security ` +
+        `service answers for '${ancestors[ancestors.length - 1]}'.`,
+      );
+    }
+    if (ancestors.length >= READABLE_IDS_MAX_CHAIN_DEPTH) {
+      throw readableIdsRefusalError(
+        object,
+        `${operation}('${object}'): ${describeReadableIdsLeaf(site.at, site.leaf)}, and the engine composes no ` +
+        `such leaf: the chain of read scopes ${branch.join(' -> ')} is ${ancestors.length + 1} scopes deep, and the ` +
+        `engine composes a chain at most ${READABLE_IDS_MAX_CHAIN_DEPTH} scopes deep. The query was NOT run and ` +
+        `no driver was asked. A master-detail chain this deep is not one the engine composes; read '${parent}' as ` +
+        'the caller first and match its ids with a list, or shorten the chain.',
+      );
+    }
+    const answer = chain.security.kind === 'usable'
+      ? await this.readableIdsScopeOf(object, operation, parent, chain.security.svc, chain.context)
+      : null;
+    if (answer === null || answer.scope === undefined) {
+      chain.answers.set(parent, answer);
+      continue;
+    }
+    // The scope is the `where` of a read of `parent`: judged as one, and
+    // the leaves it carries are composed before this parent's leaf is.
+    const nested = collectComposableReadableIds(object, operation, answer.scope, 'where', `${site.at}.scope`);
+    chain.answers.set(parent, nested.length === 0
+      ? answer
+      : { scope: await this.composeReadableIdsChain(chain, answer.scope, nested, [...ancestors, parent]) });
+  }
+  // A parent with no answer (`null`, or never asked: not registered) is
+  // `$in: []`.
+  return composeReadableIdsLeaves(node, (leaf) => {
+    const answer = chain.answers.get(leaf.object);
+    return answer ? ReadableIds.compose(leaf, answer.scope) : [];
+  });
+}
+
+/** The body of `ObjectQL#findUnservableControlledByParentMasters`; the method's docblock there is its contract. */
+export function findUnservableControlledByParentMasters(
+  this: Pick<ReadableIdsPermissionFormulaHost, '_registry' | 'uncomposableReadableIdsParent'>,
+): UnservableControlledByParentMaster[] {
+  const found: UnservableControlledByParentMaster[] = [];
+  for (const object of this._registry.getAllObjects() as Array<{ name?: string; sharingModel?: unknown; fields?: Record<string, unknown> }>) {
+    if (object?.sharingModel !== 'controlled_by_parent' || typeof object.name !== 'string') continue;
+    const masters = Object.entries(object.fields ?? {}).filter(([, f]) => isControlledByParentMasterField(f));
+    if (masters.length !== 1) continue;
+    const [field, def] = masters[0];
+    const master = (def as { reference?: unknown }).reference;
+    if (typeof master !== 'string' || !this._registry.getObject(master)) continue;
+    const uncomposable = this.uncomposableReadableIdsParent(object.name, master);
+    if (uncomposable) found.push({ detail: object.name, field, master, ...uncomposable });
+  }
+  return found;
+}
+
+/** The body of `ObjectQL#readableIdsScopeOf`; the method's docblock there is its contract. */
+export async function readableIdsScopeOf(
+  this: Pick<ReadableIdsPermissionFormulaHost, 'logger'>,
+  object: string,
+  operation: string,
+  parent: string,
+  svc: ReadableIdsSecurity,
+  context: ExecutionContext | undefined,
+): Promise<{ scope: FilterCondition | undefined } | null> {
+  const deny = (why: string, e?: unknown): null => {
+    this.logger.warn(
+      `[ObjectQL] ${operation}('${object}'): the ReadableIds leaf over '${parent}' is answered $in: [] ` +
+      `(fail-closed) — ${why}`,
+      e === undefined ? undefined : writeFailureLogMeta(e, { object, parent }),
+    );
+    return null;
+  };
+  let admitted: boolean;
+  try {
+    admitted = typeof svc.canReadObject === 'function'
+      ? (await svc.canReadObject(parent, context)) === true
+      : (await svc.explain!({ object: parent, operation: 'read' }, context))?.allowed === true;
+  } catch (e) {
+    return deny('the object-level read admission threw', e);
+  }
+  if (!admitted) return null;
+  let scope: unknown;
+  try {
+    scope = await svc.getReadFilter(parent, context);
+  } catch (e) {
+    return deny('getReadFilter() threw', e);
+  }
+  if (scope === undefined) return { scope: undefined };
+  if (scope === RLS_DENY_FILTER) return null;
+  if (scope === null || typeof scope !== 'object' || Array.isArray(scope)) {
+    return deny(`getReadFilter() answered ${scope === null ? 'null' : Array.isArray(scope) ? 'an array' : typeof scope}, not a filter`);
+  }
+  return { scope: markFilterSubtreeProvenance(scope as FilterCondition, 'policy') };
+}
+
+/** The body of `ObjectQL#resolveOptionPermissions`; the method's docblock there is its contract. */
+export async function resolveOptionPermissions(
+  schema: unknown,
+  payloads: ReadonlyArray<Record<string, unknown> | null | undefined>,
+  resolution: PermissionResolution | undefined,
+): Promise<(payload: Record<string, unknown> | null | undefined) => EvalPermissions | undefined> {
+  const none = (): undefined => undefined;
+  // [#20082] The write's ONE resolution ({@link permissionResolution}) —
+  // `undefined` on exactly the two conditions this method used to test
+  // itself: no resolver registered, or no acting user.
+  if (!resolution) return none;
+  const fields = (schema as { fields?: Parameters<typeof optionVisibilityReadsPermissions>[0] } | null | undefined)?.fields;
+  const needs = (payload: Record<string, unknown> | null | undefined): boolean =>
+    optionVisibilityReadsPermissions(fields, payload);
+  if (!payloads.some(needs)) return none;
+  let permissions: EvalPermissions;
+  try {
+    permissions = await resolution.get();
+  } catch (err) {
+    return (payload) => {
+      if (needs(payload)) throw err;
+      return undefined;
+    };
+  }
+  return (payload) => (needs(payload) ? permissions : undefined);
+}
+
+/** The body of `ObjectQL#permissionResolution`; the method's docblock there is its contract. */
+export function permissionResolution(
+  this: Pick<ReadableIdsPermissionFormulaHost, '_effectiveObjectPermissionsResolver' | 'buildEvalUser'>,
+  context: ExecutionContext | undefined,
+): PermissionResolution | undefined {
+  const resolver = this._effectiveObjectPermissionsResolver;
+  if (!resolver || !this.buildEvalUser(context)) return undefined;
+  let pending: Promise<EvalPermissions> | undefined;
+  return {
+    // `Promise.resolve().then(...)` so a resolver that throws SYNCHRONOUSLY is
+    // memoised as a rejection too, rather than escaping `get()` un-memoised
+    // and being asked again by the next consumer.
+    get: () => (pending ??= Promise.resolve()
+      .then(() => resolver(context))
+      .then((answer) => toEvalPermissions(answer))),
+  };
+}
+
+/** The body of `ObjectQL#resolveFormulaPermissions`; the method's docblock there is its contract. */
+export async function resolveFormulaPermissions(
+  this: Pick<ReadableIdsPermissionFormulaHost, 'logger'>,
+  object: string,
+  plan: readonly FormulaPlanEntry[],
+  records: readonly unknown[],
+  context: ExecutionContext | undefined,
+  resolution: PermissionResolution | undefined,
+): Promise<EvalPermissions | undefined> {
+  if (!context?.userId) return undefined;
+  if (!records.some((r) => r != null && typeof r === 'object')) return undefined;
+  const fields = plan.filter((entry) => readsPermissionPredicate(entry.expression)).map((entry) => entry.name);
+  if (fields.length === 0) return undefined;
+  if (!resolution) {
+    this.logger.warn(
+      `formula field(s) ${fields.join(', ')} on '${object}' call current_user.can(), and no `
+      + 'effective-permission source is registered, so they read null: compose a security '
+      + 'service that registers one (registerEffectiveObjectPermissionsResolver) for can() to '
+      + 'be answered',
+      { object, fields, reason: 'no-permission-source' },
+    );
+    return undefined;
+  }
+  try {
+    return await resolution.get();
+  } catch (error) {
+    this.logger.warn(
+      `formula field(s) ${fields.join(', ')} on '${object}' call current_user.can(), and the `
+      + 'effective-permission resolution failed, so they read null on this read (failed closed: '
+      + 'neither a grant nor a denial was assumed)',
+      { object, fields, reason: 'permission-resolution-failed', error },
+    );
+    return undefined;
+  }
+}
+
+/** The body of `ObjectQL#reportFormulaFault`; the method's docblock there is its contract. */
+export function reportFormulaFault(
+  this: Pick<ReadableIdsPermissionFormulaHost, 'formulaFaultReported' | 'logger'>,
+  object: string,
+  field: string,
+  error: EvalError,
+): void {
+  const key = JSON.stringify([object, field]);
+  if (this.formulaFaultReported.has(key)) return;
+  this.formulaFaultReported.add(key);
+  // The evaluator's message carries the source and a caret on the lines after
+  // its first; the first line goes in the sentence, the whole of it in the meta.
+  const headline = error.message.split('\n', 1)[0];
+  this.logger.warn(
+    `formula field '${field}' on '${object}' could not be evaluated, so it reads null wherever this `
+    + `fault holds (${error.kind}: ${headline}). If the expression itself is at fault — an unknown `
+    + 'function, a missing field — `os validate`, or a re-save of the object, refuses it with a located '
+    + 'message; if it faults on some records\' values, guard the operands it reads. Reported once per '
+    + 'object and field per engine instance.',
+    { object, field, kind: error.kind, error: error.message },
+  );
+}
+
+/** The body of `ObjectQL#resolveDefaultPermissions`; the method's docblock there is its contract. */
+export async function resolveDefaultPermissions(
+  this: Pick<ReadableIdsPermissionFormulaHost, 'defaultFieldEntries'>,
+  object: string,
+  rows: ReadonlyArray<unknown>,
+  context: ExecutionContext | undefined,
+  resolution: PermissionResolution | undefined,
+  onlyFields?: readonly string[],
+): Promise<(row: unknown) => EvalPermissions | undefined> {
+  const none = (): undefined => undefined;
+  if (!resolution || !context?.userId) return none;
+  const gated = (this.defaultFieldEntries(object) ?? [])
+    .filter((f) => !onlyFields || onlyFields.includes(f.name))
+    .filter((f) => isExpressionDefault(f.defaultValue) && readsPermissionPredicate(f.defaultValue))
+    .map((f) => f.name);
+  if (gated.length === 0) return none;
+  const needs = (row: unknown): boolean =>
+    row != null && typeof row === 'object'
+    && gated.some((name) => (row as Record<string, unknown>)[name] == null);
+  if (!rows.some(needs)) return none;
+  let permissions: EvalPermissions;
+  try {
+    permissions = await resolution.get();
+  } catch (err) {
+    return (row) => {
+      if (needs(row)) throw err;
+      return undefined;
+    };
+  }
+  return (row) => (needs(row) ? permissions : undefined);
+}