diff --git a/packages/plugins/plugin-security/src/explain-controlled-by-parent-master-modify-all.test.ts b/packages/plugins/plugin-security/src/explain-controlled-by-parent-master-modify-all.test.ts
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+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+//
+// [ADR-0055] `security/explain`'s record-grained verdict for an update and a
+// delete of a `controlled_by_parent` record whose MASTER the caller may edit
+// through `modifyAllRecords` on the master alone, beside the door's answer for
+// the same caller and row.
+//
+// ## Why this route has its own file
+//
+// The console's record header asks exactly this question: it posts
+// `security/explain` with a `recordId`, once for `update` and once for
+// `delete`, and shows Edit and Delete on `decision.record.visible`. A sales
+// manager who holds `viewAllRecords` + `modifyAllRecords` on the master (the
+// account) and plain edit on the detail (a contract, a quote) reaches the
+// detail's rows only through the master: the detail grants no bypass of its
+// own, and the master is owned and created by somebody else.
+//
+// The routes to the master that the explain/door pair already pins beside each
+// other (`controlled-by-parent-write-member.test.ts`, and the REST twin
+// `packages/qa/dogfood/test/cbp-explain-master-write.dogfood.test.ts`) are an
+// owned master, a master shared at `edit`, a master an RLS policy admits and a
+// two-hop chain. None of them is the Modify All Data bypass, which the master
+// check reaches by two seams of its own: the master's ownership floor comes off
+// on the sharing write verdict `allow` that the bypass answers, and the master's
+// record-sharing leg is the bypass branch of `canEdit`. This file pins that
+// route, with the floor armed on both objects.
+//
+// ## The control
+//
+// The viewer holds `viewAllRecords` on the master WITHOUT `modifyAllRecords`:
+// the near neighbour of the manager's grant. They read every master and every
+// detail, and may edit neither the master nor, therefore, its details. Both
+// faces must refuse them, and explain must name the master check's leg. A read
+// bypass that leaked into a write verdict, or an explanation that stopped
+// asking the master check, fails this half.
+//
+// ## The rig
+//
+// The real `SecurityPlugin` over a real `ObjectQL` and SQL driver
+// (better-sqlite3, in memory), the real `SharingService` as the kernel's
+// `sharing` service with its middleware on the engine after this plugin's, and
+// the platform's own `member_default` set, whose wildcard `owner_only_writes` /
+// `owner_only_deletes` floor (`created_by == current_user.id`, positions
+// `['org_member']`) is armed for both callers. The armed case below shows it
+// binding each of them on this stack, through explain's own `rls` record.
+//
+// `@objectstack/core` and `@objectstack/plugin-sharing` resolve through their
+// built `dist/` here, as this package's other suites read them.
+
+import { describe, it, expect, beforeAll, afterAll, vi } from 'vitest';
+import { ObjectQL } from '@objectstack/objectql';
+import { SqlDriver } from '@objectstack/driver-sql';
+import { SharingService, buildSharingMiddleware, SysRecordShare } from '@objectstack/plugin-sharing';
+import { PermissionSetSchema } from '@objectstack/spec/security';
+import type { ExplainDecision } from '@objectstack/spec/security';
+import { SecurityPlugin } from './security-plugin.js';
+import { defaultPermissionSets } from './objects/default-permission-sets.js';
+
+const SYS = { context: { isSystem: true } } as never;
+const MEMBER_DEFAULT = defaultPermissionSets.find((p) => p.name === 'member_default')!;
+
+const ACCOUNT = 'cbm_account';
+const CONTRACT = 'cbm_contract';
+/**
+ * The floor witness: an object with no master and no owner column, whose rows
+ * neither caller created. Explaining a write of one shows the floor's own
+ * predicate in the `rls` record, for each caller.
+ */
+const MEMO = 'cbm_memo';
+
+/** The master's owner and creator, and the creator of every detail row: nobody the suite explains. */
+const REP = 'usr_rep';
+const MANAGER = 'usr_manager';
+const VIEWER = 'usr_viewer';
+
+const CRUD = { allowRead: true, allowCreate: true, allowEdit: true, allowDelete: true };
+
+/** Modify All Data on the master only; the detail grants plain CRUD, reads included, and no write bypass. */
+const MANAGER_SET = PermissionSetSchema.parse({
+  name: 'cbm_manager',
+  objects: {
+    [ACCOUNT]: { ...CRUD, viewAllRecords: true, modifyAllRecords: true },
+    [CONTRACT]: { ...CRUD, viewAllRecords: true, modifyAllRecords: false },
+    [MEMO]: { allowRead: true, allowEdit: true, viewAllRecords: true },
+  },
+});
+
+/** The control: the same grants with the master's write bypass withheld. */
+const VIEWER_SET = PermissionSetSchema.parse({
+  name: 'cbm_viewer',
+  objects: {
+    [ACCOUNT]: { allowRead: true, allowCreate: true, allowEdit: true, viewAllRecords: true, modifyAllRecords: false },
+    [CONTRACT]: { ...CRUD, viewAllRecords: true, modifyAllRecords: false },
+    [MEMO]: { allowRead: true, allowEdit: true, viewAllRecords: true },
+  },
+});
+
+/** The execution context `resolveAuthzContext` hands the middleware for an organization member holding the set. */
+const callerOf = (userId: string, set: string) => ({
+  userId,
+  positions: ['org_member'],
+  permissions: [set, 'member_default'],
+  posture: 'MEMBER',
+});
+const MANAGER_CALLER = callerOf(MANAGER, MANAGER_SET.name);
+const VIEWER_CALLER = callerOf(VIEWER, VIEWER_SET.name);
+
+type Answer = { kind: 'admitted' } | { kind: 'refused'; code?: string; status?: number; message: string };
+
+const landed = (p: Promise<unknown>): Promise<Answer> =>
+  p.then(
+    () => ({ kind: 'admitted' as const }),
+    (e: any) => ({
+      kind: 'refused' as const,
+      code: e?.code == null ? undefined : String(e.code),
+      status: e?.statusCode ?? e?.status,
+      message: `${String(e?.message ?? '')} ${String(e?.developerMessage ?? '')}`,
+    }),
+  );
+
+let engine: ObjectQL;
+let plugin: SecurityPlugin;
+
+beforeAll(async () => {
+  engine = new ObjectQL();
+  engine.registerDriver(
+    new SqlDriver({ client: 'better-sqlite3', connection: { filename: ':memory:' }, useNullAsDefault: true }) as never,
+    true,
+  );
+  await engine.init();
+  engine.registerApp({
+    id: 'com.objectstack.qa.explain-controlled-by-parent-master-modify-all',
+    name: 'Explain: a controlled_by_parent record under a master edited through Modify All Data',
+    version: '1.0.0',
+    type: 'plugin',
+    scope: 'system',
+    objects: [
+      SysRecordShare,
+      {
+        name: ACCOUNT,
+        label: 'Account',
+        sharingModel: 'private',
+        tenancy: { enabled: false },
+        fields: {
+          id: { name: 'id', type: 'text', primaryKey: true },
+          name: { name: 'name', type: 'text' },
+          owner_id: { name: 'owner_id', type: 'text' },
+          created_by: { name: 'created_by', type: 'text' },
+        },
+      },
+      {
+        name: CONTRACT,
+        label: 'Contract',
+        sharingModel: 'controlled_by_parent',
+        tenancy: { enabled: false },
+        fields: {
+          id: { name: 'id', type: 'text', primaryKey: true },
+          name: { name: 'name', type: 'text' },
+          account: { name: 'account', type: 'master_detail', reference: ACCOUNT, required: true },
+          created_by: { name: 'created_by', type: 'text' },
+        },
+      },
+      {
+        name: MEMO,
+        label: 'Memo',
+        sharingModel: 'private',
+        tenancy: { enabled: false },
+        fields: {
+          id: { name: 'id', type: 'text', primaryKey: true },
+          name: { name: 'name', type: 'text' },
+          created_by: { name: 'created_by', type: 'text' },
+        },
+      },
+    ],
+  } as never);
+  await engine.syncSchemas();
+  await engine.insert(ACCOUNT, [{ id: 'acct_rep', name: "the rep's account", owner_id: REP, created_by: REP }], SYS);
+  // One detail row per (caller, verb), so a delete that lands never changes another case's row.
+  await engine.insert(CONTRACT, [
+    { id: 'c_manager_update', name: 'contract', account: 'acct_rep', created_by: REP },
+    { id: 'c_manager_delete', name: 'contract', account: 'acct_rep', created_by: REP },
+    { id: 'c_viewer_update', name: 'contract', account: 'acct_rep', created_by: REP },
+    { id: 'c_viewer_delete', name: 'contract', account: 'acct_rep', created_by: REP },
+  ], SYS);
+  await engine.insert(MEMO, [{ id: 'm_rep', name: "the rep's memo", created_by: REP }], SYS);
+
+  const sets = [MEMBER_DEFAULT, MANAGER_SET, VIEWER_SET];
+  let security: unknown;
+  let sharing: SharingService | undefined;
+  const services: Record<string, unknown> = {
+    manifest: { register: vi.fn() },
+    objectql: engine,
+    metadata: {
+      get: async (type: string, name: string) =>
+        type === 'permission' ? sets.find((s) => s.name === name) ?? null : engine.getSchema(name) ?? null,
+      list: async () => sets,
+    },
+    get sharing() { return sharing; },
+  };
+  const ctx = {
+    logger: { info: vi.fn(), warn: vi.fn(), error: vi.fn(), debug: vi.fn() },
+    registerService: (name: string, svc: unknown) => { if (name === 'security') security = svc; },
+    // The lifecycle hooks are collected and never fired, so no bootstrap read
+    // is left running into the engine teardown.
+    hook: () => undefined,
+    getService: (name: string) => {
+      if (!(name in services)) throw new Error(`service not registered: ${name}`);
+      return services[name];
+    },
+  };
+  plugin = new SecurityPlugin({ fallbackPermissionSet: 'member_default' });
+  await plugin.init(ctx as never);
+  await plugin.start(ctx as never);
+  sharing = new SharingService({ engine: engine as never, securityService: () => security as never });
+  engine.registerMiddleware(buildSharingMiddleware(sharing, ctx.logger) as never, { object: '*' });
+});
+
+afterAll(async () => {
+  try { await engine?.destroy(); } catch { /* noop */ }
+});
+
+const explain = (operation: 'update' | 'delete', recordId: string, caller: object): Promise<ExplainDecision> =>
+  plugin.explainAccessForCaller({ object: CONTRACT, operation, recordId }, { ...caller });
+
+const door = (operation: 'update' | 'delete', recordId: string, caller: object): Promise<Answer> =>
+  operation === 'update'
+    ? landed(engine.update(CONTRACT, { name: 'edited' }, { where: { id: recordId }, context: { ...caller } } as never))
+    : landed(engine.delete(CONTRACT, { where: { id: recordId }, context: { ...caller } } as never));
+
+const sharingDetailOf = (d: ExplainDecision): string =>
+  String(d.layers.find((l) => l.layer === 'sharing')?.record?.detail ?? '');
+
+describe('[ADR-0055] explain answers a controlled_by_parent write under a Modify All Data master as the door does', () => {
+  it('armed: every row was created by another user, and the ownership floor binds both callers on this stack', async () => {
+    const stored = (await engine.find(CONTRACT, { where: {}, context: { isSystem: true } } as never)) as Array<Record<string, unknown>>;
+    expect(stored.map((r) => r.created_by)).toEqual([REP, REP, REP, REP]);
+    // The floor is the only update policy these sets carry: explained on a row
+    // the caller did not create, the `rls` record names its predicate,
+    // `created_by == current_user.id`, and it excludes the row.
+    for (const caller of [MANAGER_CALLER, VIEWER_CALLER]) {
+      const d = await plugin.explainAccessForCaller({ object: MEMO, operation: 'update', recordId: 'm_rep' }, { ...caller });
+      const rls = d.layers.find((l) => l.layer === 'rls')?.record;
+      expect(rls?.rowFilter, `the floor's predicate for ${caller.userId}`).toEqual({ created_by: caller.userId });
+      expect(rls?.outcome).toBe('excluded');
+    }
+  });
+
+  for (const verb of ['update', 'delete'] as const) {
+    it(`${verb}: the master's Modify All Data holder, who created neither row, is explained writable and the door admits`, async () => {
+      const id = `c_manager_${verb}`;
+      const explained = await explain(verb, id, MANAGER_CALLER);
+      const answered = await door(verb, id, MANAGER_CALLER);
+      expect(answered, `${verb} door, the manager`).toEqual({ kind: 'admitted' });
+      expect(explained.record, `explain ${verb}, the manager`).toMatchObject({ recordId: id, visible: true });
+      expect(sharingDetailOf(explained)).not.toContain('master-detail write check');
+    });
+
+    it(`${verb}: control, the master's reader without Modify All Data is refused by both, on the master leg`, async () => {
+      const id = `c_viewer_${verb}`;
+      const explained = await explain(verb, id, VIEWER_CALLER);
+      const answered = await door(verb, id, VIEWER_CALLER);
+      expect(answered, `${verb} door, the viewer`).toMatchObject({ kind: 'refused', code: 'PERMISSION_DENIED', status: 403 });
+      expect((answered as { message: string }).message).toMatch(/requires edit access to its master record/);
+      expect(explained.record, `explain ${verb}, the viewer`).toEqual({ recordId: id, visible: false, decidedBy: 'sharing' });
+      expect(sharingDetailOf(explained)).toMatch(new RegExp(`refuses this ${verb} on its '[a-z_]+' leg`));
+    });
+  }
+
+  it("reference: the master's own door gives the two callers the answers the master check gives them", async () => {
+    const asManager = await landed(engine.update(ACCOUNT, { name: 'renamed' }, { where: { id: 'acct_rep' }, context: { ...MANAGER_CALLER } } as never));
+    const asViewer = await landed(engine.update(ACCOUNT, { name: 'renamed' }, { where: { id: 'acct_rep' }, context: { ...VIEWER_CALLER } } as never));
+    expect(asManager, 'the manager PATCHes the master').toEqual({ kind: 'admitted' });
+    expect(asViewer, 'the viewer PATCHes the master').toMatchObject({ kind: 'refused', code: 'PERMISSION_DENIED', status: 403 });
+  });
+});