feat(hierarchy): audit event + outbox machinery (M4-1b-i, contract 1 §5.2)

- hierarchy_audit_events: append-only semantic events (actor, verb, target
  snapshot with root-first parent chain), deletion-safe linkage (no FK into
  class tables), CHECK-enforced verb/target-kind/transfer shape, unique
  idempotency key, generated-always seq for per-target ordering, causation
  self-FK RESTRICT; hierarchy_outbox: dedicated same-transaction outbox
  (unique event_id, status enum, claim-by-CAS lifecycle) — migration 0019
- gateway HierarchyAuditRepository: same-tx append with idempotent replay
  (canonical-JSON compare, jsonb key order independent), snapshot builder,
  per-target history, outbox claim/complete/release; HierarchyModule exposes
  no routes yet (command family lands in M4-1b-ii after contract 2 merges)
- dual-leg schema witnesses (PGlite + real PG) for every constraint above;
  repository §6.4 witnesses: atomic commit, rollback residue-free, replay,
  conflicting-key refusal, events survive target deletion, CAS races
- §6.3(a) route-inventory baseline: enumerates the AppModule route surface,
  pins zero hierarchy mutation routes until M4-1b-ii
- writer-coverage scan perimeter widened from <pkg>/src to the full package
  tree (S1 residual; widened set measured free of all trigger tokens)

apps/gateway/src/__tests__/hierarchy-route-inventory.test.ts

@@ -0,0 +1,106 @@
+import { RequestMethod, type Type } from '@nestjs/common';
+import { describe, expect, it } from 'vitest';
+import { AppModule } from '../app.module.js';
+import { HierarchyModule } from '../hierarchy/hierarchy.module.js';
+
+/**
+ * Hierarchy route-inventory baseline (contract 1 §6.3(a)).
+ *
+ * M4-1b-i ships the audit event + outbox machinery with NO mutation routes:
+ * the hierarchy command family (controllers + DTOs) lands in M4-1b-ii once
+ * contract 2 merges. This witness enumerates every route the AppModule graph
+ * declares and pins that baseline, so a hierarchy route appearing before its
+ * command-family witnesses exist fails here first. When M4-1b-ii lands, this
+ * baseline is replaced by an exact inventory of the command family.
+ */
+
+interface RouteEntry {
+  method: string;
+  path: string;
+  controller: string;
+}
+
+/** Module-metadata entry: a module class or a DynamicModule-shaped object. */
+type ModuleEntry =
+  | Type<unknown>
+  | { module: Type<unknown>; imports?: unknown[]; controllers?: Type<unknown>[] };
+
+function collectControllers(root: ModuleEntry): Type<unknown>[] {
+  const visited = new Set<unknown>();
+  const controllers: Type<unknown>[] = [];
+  const walk = (entry: ModuleEntry | undefined | null): void => {
+    if (!entry || visited.has(entry)) return;
+    visited.add(entry);
+    const moduleClass = typeof entry === 'function' ? entry : entry.module;
+    // Entries with no resolvable class (forwardRef wrappers, async dynamic
+    // modules) carry no decorator metadata to read here.
+    if (typeof moduleClass !== 'function') return;
+    if (visited.has(moduleClass) && typeof entry !== 'function') return;
+    visited.add(moduleClass);
+    // 'controllers' / 'imports' are the metadata keys the @Module decorator writes.
+    const declared = (Reflect.getMetadata('controllers', moduleClass) ?? []) as Type<unknown>[];
+    controllers.push(...declared);
+    if (typeof entry !== 'function' && entry.controllers) controllers.push(...entry.controllers);
+    const imports = [
+      ...((Reflect.getMetadata('imports', moduleClass) ?? []) as ModuleEntry[]),
+      ...(typeof entry !== 'function' ? ((entry.imports ?? []) as ModuleEntry[]) : []),
+    ];
+    for (const imported of imports) walk(imported);
+  };
+  walk(root);
+  return controllers;
+}
+
+function routesOf(controller: Type<unknown>): RouteEntry[] {
+  // 'path' on the class is the @Controller prefix; 'path'/'method' on a
+  // handler are written by the @Get/@Post/... route decorators.
+  const base = (Reflect.getMetadata('path', controller) ?? '') as string | string[];
+  const bases = Array.isArray(base) ? base : [base];
+  const routes: RouteEntry[] = [];
+  const prototype = controller.prototype as Record<string, unknown>;
+  for (const name of Object.getOwnPropertyNames(prototype)) {
+    if (name === 'constructor') continue;
+    const handler = Object.getOwnPropertyDescriptor(prototype, name)?.value;
+    if (typeof handler !== 'function') continue;
+    const method = Reflect.getMetadata('method', handler) as number | undefined;
+    if (method === undefined) continue;
+    const sub = (Reflect.getMetadata('path', handler) ?? '/') as string;
+    for (const prefix of bases) {
+      const path = `/${prefix}/${sub}`.replace(/\/+/g, '/').replace(/(.)\/$/, '$1');
+      routes.push({
+        method: RequestMethod[method] ?? String(method),
+        path,
+        controller: controller.name,
+      });
+    }
+  }
+  return routes;
+}
+
+describe('hierarchy route-inventory baseline (§6.3(a))', () => {
+  const inventory = collectControllers(AppModule).flatMap(routesOf);
+
+  it('control: the enumeration sees the known route surface', () => {
+    const paths = inventory.map((r) => `${r.method} ${r.path}`);
+    expect(paths).toContain('GET /health');
+    expect(paths).toContain('POST /api/workspaces');
+    expect(paths).toContain('GET /api/teams');
+    expect(inventory.length).toBeGreaterThan(20);
+  });
+
+  it('declares zero hierarchy mutation routes before M4-1b-ii', () => {
+    const hierarchyRoutes = inventory.filter((r) =>
+      /hierarch|compan|estate|platform[-_]?project/i.test(r.path),
+    );
+    expect(
+      hierarchyRoutes,
+      'a hierarchy route landed without replacing the §6.3(a) baseline with a command-family inventory',
+    ).toEqual([]);
+  });
+
+  it('HierarchyModule itself declares no controllers', () => {
+    expect((Reflect.getMetadata('controllers', HierarchyModule) ?? []) as unknown[]).toEqual([]);
+    const hierarchyControllers = collectControllers(HierarchyModule);
+    expect(hierarchyControllers).toEqual([]);
+  });
+});

apps/gateway/src/app.module.ts

@@ -24,6 +24,7 @@ import { GCModule } from './gc/gc.module.js';
 import { HarnessModule } from './harness/harness.module.js';
 import { ReloadModule } from './reload/reload.module.js';
 import { WorkspaceModule } from './workspace/workspace.module.js';
+import { HierarchyModule } from './hierarchy/hierarchy.module.js';
 import { QueueModule } from './queue/queue.module.js';
 import { FederationModule } from './federation/federation.module.js';
 import { ThrottlerGuard, ThrottlerModule } from '@nestjs/throttler';
@@ -65,6 +66,7 @@ const federationEnabled = loadConfig(resolveGatewayConfigPath()).tier === 'feder
     QueueModule,
     ReloadModule,
     WorkspaceModule,
+    HierarchyModule,
     ...(federationEnabled ? [FederationModule] : []),
   ],
   controllers: [HealthController],

apps/gateway/src/hierarchy/hierarchy-audit.integration.test.ts

@@ -0,0 +1,226 @@
+import { mkdtemp, rm } from 'node:fs/promises';
+import { randomUUID } from 'node:crypto';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+import { afterAll, beforeAll, describe, expect, it } from 'vitest';
+import { Test, type TestingModule } from '@nestjs/testing';
+import {
+  companies,
+  createPgliteDb,
+  eq,
+  estates,
+  hierarchyAuditEvents,
+  hierarchyOutbox,
+  platformProjects,
+  runPgliteMigrations,
+  type DbHandle,
+} from '@mosaicstack/db';
+import { DB } from '../database/database.module.js';
+import {
+  HierarchyAuditIdempotencyConflictError,
+  HierarchyAuditRepository,
+  HierarchyNodeNotFoundError,
+  type AppendHierarchyEventInput,
+} from './hierarchy-audit.repository.js';
+
+/**
+ * Repository-level §6.4 witnesses for the hierarchy audit machinery
+ * (contract 1 §5.2, REQ-AUD-001): same-transaction atomicity of state +
+ * event + outbox, rollback leaving no residue, idempotent replay, snapshot
+ * parent chains, events surviving target deletion, per-target ordering, and
+ * the outbox claim/complete/release CAS. The schema-level constraints are
+ * witnessed in packages/db/src/hierarchy-audit.witness.test.ts.
+ */
+describe('hierarchy audit repository integration', (): void => {
+  let dataDir: string;
+  let handle: DbHandle;
+  let moduleRef: TestingModule;
+  let repo: HierarchyAuditRepository;
+
+  const input = (
+    overrides: Partial<AppendHierarchyEventInput> = {},
+  ): AppendHierarchyEventInput => ({
+    actorId: 'user-actor',
+    verb: 'create',
+    targetKind: 'company',
+    targetId: randomUUID(),
+    targetSnapshot: { id: 'x', slug: 'x', name: 'x', parentChain: [] },
+    correlationId: 'corr-1',
+    idempotencyKey: `key-${randomUUID()}`,
+    ...overrides,
+  });
+
+  beforeAll(async (): Promise<void> => {
+    dataDir = await mkdtemp(join(tmpdir(), 'mosaic-gateway-hierarchy-audit-'));
+    handle = createPgliteDb(dataDir);
+    await runPgliteMigrations(handle);
+    moduleRef = await Test.createTestingModule({
+      providers: [HierarchyAuditRepository, { provide: DB, useValue: handle.db }],
+    }).compile();
+    repo = moduleRef.get(HierarchyAuditRepository);
+  });
+
+  afterAll(async (): Promise<void> => {
+    await moduleRef.close();
+    await handle.close();
+    await rm(dataDir, { recursive: true, force: true });
+  });
+
+  it('commits state, event, and outbox record atomically in one transaction', async () => {
+    const companyId = randomUUID();
+    const key = `key-${randomUUID()}`;
+    await handle.db.transaction(async (tx) => {
+      await tx.insert(companies).values({ id: companyId, name: 'Atomic Co', slug: 'atomic-co' });
+      const snapshot = await repo.snapshot(tx, 'company', companyId);
+      const result = await repo.append(tx, {
+        ...input({ targetId: companyId, idempotencyKey: key }),
+        targetSnapshot: { ...snapshot },
+      });
+      expect(result.replayed).toBe(false);
+      expect(result.event.idempotencyKey).toBe(key);
+    });
+    const events = await handle.db
+      .select()
+      .from(hierarchyAuditEvents)
+      .where(eq(hierarchyAuditEvents.idempotencyKey, key));
+    expect(events).toHaveLength(1);
+    const outbox = await handle.db
+      .select()
+      .from(hierarchyOutbox)
+      .where(eq(hierarchyOutbox.eventId, events[0]!.id));
+    expect(outbox).toHaveLength(1);
+    expect(outbox[0]).toMatchObject({
+      status: 'pending',
+      idempotencyKey: key,
+      correlationId: 'corr-1',
+    });
+  });
+
+  it('a rolled-back transaction leaves no state, no event, and no outbox record', async () => {
+    const companyId = randomUUID();
+    const key = `key-${randomUUID()}`;
+    await expect(
+      handle.db.transaction(async (tx) => {
+        await tx.insert(companies).values({ id: companyId, name: 'Doomed Co', slug: 'doomed-co' });
+        await repo.append(tx, input({ targetId: companyId, idempotencyKey: key }));
+        throw new Error('deliberate rollback');
+      }),
+    ).rejects.toThrow('deliberate rollback');
+    const [companyRows, eventRows, outboxRows] = await Promise.all([
+      handle.db.select().from(companies).where(eq(companies.id, companyId)),
+      handle.db
+        .select()
+        .from(hierarchyAuditEvents)
+        .where(eq(hierarchyAuditEvents.idempotencyKey, key)),
+      handle.db.select().from(hierarchyOutbox).where(eq(hierarchyOutbox.idempotencyKey, key)),
+    ]);
+    expect(companyRows).toHaveLength(0);
+    expect(eventRows).toHaveLength(0);
+    expect(outboxRows).toHaveLength(0);
+  });
+
+  it('replays a duplicate idempotency key without inserting a second event or outbox record', async () => {
+    const first = input();
+    const original = await handle.db.transaction(async (tx) => repo.append(tx, first));
+    const replay = await handle.db.transaction(async (tx) => repo.append(tx, first));
+    expect(original.replayed).toBe(false);
+    expect(replay.replayed).toBe(true);
+    expect(replay.event.id).toBe(original.event.id);
+    const outbox = await handle.db
+      .select()
+      .from(hierarchyOutbox)
+      .where(eq(hierarchyOutbox.eventId, original.event.id));
+    expect(outbox).toHaveLength(1);
+  });
+
+  it('throws on a duplicate idempotency key carrying different event content', async () => {
+    const first = input();
+    await handle.db.transaction(async (tx) => repo.append(tx, first));
+    await expect(
+      handle.db.transaction(async (tx) =>
+        repo.append(tx, { ...first, verb: 'rename', targetId: randomUUID() }),
+      ),
+    ).rejects.toThrow(HierarchyAuditIdempotencyConflictError);
+  });
+
+  it('builds root-first parent chains and rejects unknown nodes', async () => {
+    const companyId = randomUUID();
+    const estateId = randomUUID();
+    const projectId = randomUUID();
+    await handle.db.transaction(async (tx) => {
+      await tx.insert(companies).values({ id: companyId, name: 'Chain Co', slug: 'chain-co' });
+      await tx
+        .insert(estates)
+        .values({ id: estateId, name: 'Chain Estate', slug: 'chain-estate', companyId });
+      await tx
+        .insert(platformProjects)
+        .values({ id: projectId, name: 'Chain Project', slug: 'chain-project', estateId });
+    });
+    const snapshot = await repo.snapshot(handle.db, 'platform_project', projectId);
+    expect(snapshot).toMatchObject({ id: projectId, slug: 'chain-project', name: 'Chain Project' });
+    expect(snapshot.parentChain).toEqual([
+      { kind: 'company', id: companyId, slug: 'chain-co' },
+      { kind: 'estate', id: estateId, slug: 'chain-estate' },
+    ]);
+    await expect(repo.snapshot(handle.db, 'estate', randomUUID())).rejects.toThrow(
+      HierarchyNodeNotFoundError,
+    );
+  });
+
+  it('keeps events readable, in per-target seq order, after the target row is deleted', async () => {
+    const companyId = randomUUID();
+    await handle.db.transaction(async (tx) => {
+      await tx.insert(companies).values({ id: companyId, name: 'Mortal Co', slug: 'mortal-co' });
+      const snapshot = await repo.snapshot(tx, 'company', companyId);
+      await repo.append(tx, input({ targetId: companyId, targetSnapshot: { ...snapshot } }));
+    });
+    await handle.db.transaction(async (tx) => {
+      const snapshot = await repo.snapshot(tx, 'company', companyId);
+      await repo.append(tx, {
+        ...input({ verb: 'delete', targetId: companyId }),
+        targetSnapshot: { ...snapshot },
+      });
+      await tx.delete(companies).where(eq(companies.id, companyId));
+    });
+    const events = await repo.eventsForTarget(companyId);
+    expect(events.map((e) => e.verb)).toEqual(['create', 'delete']);
+    expect(events[1]!.seq).toBeGreaterThan(events[0]!.seq);
+    expect((events[1]!.targetSnapshot as { id: string }).id).toBe(companyId);
+  });
+
+  it('claims the oldest pending outbox record exactly once, completes and releases by CAS', async () => {
+    // Drain records left pending by earlier cases so ordering is deterministic.
+    for (;;) {
+      const drained = await repo.claimPendingOutbox();
+      if (!drained) break;
+      await repo.completeOutbox(drained.id);
+    }
+    const older = await handle.db.transaction(async (tx) => repo.append(tx, input()));
+    const newer = await handle.db.transaction(async (tx) => repo.append(tx, input()));
+
+    const claimed = await repo.claimPendingOutbox();
+    expect(claimed).not.toBeNull();
+    expect(claimed!.eventId).toBe(older.event.id);
+    expect(claimed!.status).toBe('processing');
+
+    // Delivery fails: release returns it to pending and it is claimable again.
+    await repo.releaseOutbox(claimed!.id);
+    const reclaimed = await repo.claimPendingOutbox();
+    expect(reclaimed!.id).toBe(claimed!.id);
+
+    await repo.completeOutbox(reclaimed!.id);
+    const done = await handle.db
+      .select()
+      .from(hierarchyOutbox)
+      .where(eq(hierarchyOutbox.id, reclaimed!.id));
+    expect(done[0]!.status).toBe('delivered');
+    expect(done[0]!.deliveredAt).not.toBeNull();
+    // completeOutbox is CAS-guarded on 'processing': completing again is a no-op.
+    await repo.completeOutbox(reclaimed!.id);
+
+    const second = await repo.claimPendingOutbox();
+    expect(second!.eventId).toBe(newer.event.id);
+    await repo.completeOutbox(second!.id);
+    expect(await repo.claimPendingOutbox()).toBeNull();
+  });
+});

apps/gateway/src/hierarchy/hierarchy-audit.repository.ts

@@ -0,0 +1,270 @@
+import { Inject, Injectable } from '@nestjs/common';
+import {
+  and,
+  asc,
+  companies,
+  eq,
+  estates,
+  hierarchyAuditEvents,
+  hierarchyOutbox,
+  platformProjects,
+  type Db,
+  type HIERARCHY_AUDIT_TARGET_KINDS,
+  type HIERARCHY_AUDIT_VERBS,
+} from '@mosaicstack/db';
+import { DB } from '../database/database.module.js';
+
+/**
+ * Hierarchy audit event + outbox machinery (contract 1 §5.2).
+ *
+ * Every hierarchy mutation writes its semantic audit event AND the event's
+ * outbox record on the caller's transaction, so state, event, and outbox
+ * commit or roll back together. Events reference their target by an
+ * immutable snapshot (id, slug, parent chain at event time), never by a
+ * foreign key into the class tables — append-only events survive the
+ * deletion of their target. This module exposes no update or delete path
+ * for events: append-only is a property of the code surface, witnessed by
+ * the integration tests.
+ *
+ * This is NOT a class-table writer: it touches only the audit/outbox
+ * tables, so it does not appear on the writer-coverage allowlist. The
+ * hierarchy command repositories (M4-1b-ii) are the allowlisted writers and
+ * call into this on their own transactions.
+ */
+
+export type HierarchyAuditVerb = (typeof HIERARCHY_AUDIT_VERBS)[number];
+export type HierarchyTargetKind = (typeof HIERARCHY_AUDIT_TARGET_KINDS)[number];
+export type HierarchyNodeKind = Exclude<HierarchyTargetKind, 'grant'>;
+
+export interface ParentChainEntry {
+  readonly kind: HierarchyNodeKind;
+  readonly id: string;
+  readonly slug: string;
+}
+
+/** Immutable node snapshot at event time; parentChain is root-first. */
+export interface HierarchyNodeSnapshot {
+  readonly id: string;
+  readonly slug: string;
+  readonly name: string;
+  readonly parentChain: readonly ParentChainEntry[];
+}
+
+export interface AppendHierarchyEventInput {
+  readonly actorId: string;
+  readonly verb: HierarchyAuditVerb;
+  readonly targetKind: HierarchyTargetKind;
+  readonly targetId: string;
+  /** Node events: HierarchyNodeSnapshot. Grant events: subject/target/role snapshot (contract 2 §4.4). */
+  readonly targetSnapshot: Record<string, unknown>;
+  /** Present exactly on transfers (CHECK-enforced): source/destination parent { kind, id, slug }. */
+  readonly transferFrom?: ParentChainEntry;
+  readonly transferTo?: ParentChainEntry;
+  readonly correlationId: string;
+  /** Prior event in the causal chain (e.g. the delete event causing cascaded grant_revoke events). */
+  readonly causationId?: string;
+  readonly idempotencyKey: string;
+}
+
+export type HierarchyAuditEventRow = typeof hierarchyAuditEvents.$inferSelect;
+export type HierarchyOutboxRow = typeof hierarchyOutbox.$inferSelect;
+
+export interface AppendHierarchyEventResult {
+  readonly event: HierarchyAuditEventRow;
+  /** True when the idempotency key had already committed an identical event (REQ-AUD-001 duplicate suppression). */
+  readonly replayed: boolean;
+}
+
+type Tx = Pick<Db, 'insert' | 'select'>;
+
+export class HierarchyAuditIdempotencyConflictError extends Error {
+  constructor(idempotencyKey: string) {
+    super(
+      `hierarchy audit idempotency key ${idempotencyKey} already exists with different event content`,
+    );
+    this.name = 'HierarchyAuditIdempotencyConflictError';
+  }
+}
+
+export class HierarchyNodeNotFoundError extends Error {
+  constructor(kind: HierarchyNodeKind, id: string) {
+    super(`hierarchy node not found: ${kind} ${id}`);
+    this.name = 'HierarchyNodeNotFoundError';
+  }
+}
+
+/**
+ * Append one audit event and its outbox record on the caller's transaction.
+ * A duplicate idempotency key with identical semantic content returns the
+ * prior event (replayed: true) without inserting anything; a duplicate key
+ * with different content throws.
+ */
+export async function appendHierarchyEvent(
+  tx: Tx,
+  input: AppendHierarchyEventInput,
+): Promise<AppendHierarchyEventResult> {
+  const inserted = await tx
+    .insert(hierarchyAuditEvents)
+    .values({
+      actorId: input.actorId,
+      verb: input.verb,
+      targetKind: input.targetKind,
+      targetId: input.targetId,
+      targetSnapshot: input.targetSnapshot,
+      transferFrom: input.transferFrom ?? null,
+      transferTo: input.transferTo ?? null,
+      correlationId: input.correlationId,
+      causationId: input.causationId ?? null,
+      idempotencyKey: input.idempotencyKey,
+    })
+    .onConflictDoNothing()
+    .returning();
+  const event = inserted[0];
+  if (event) {
+    await tx.insert(hierarchyOutbox).values({
+      eventId: event.id,
+      idempotencyKey: input.idempotencyKey,
+      correlationId: input.correlationId,
+    });
+    return { event, replayed: false };
+  }
+
+  const prior = await tx
+    .select()
+    .from(hierarchyAuditEvents)
+    .where(eq(hierarchyAuditEvents.idempotencyKey, input.idempotencyKey))
+    .limit(1);
+  const existing = prior[0];
+  if (!existing || !sameEvent(existing, input)) {
+    throw new HierarchyAuditIdempotencyConflictError(input.idempotencyKey);
+  }
+  // Event and outbox committed atomically the first time, so the outbox
+  // record already exists; a replay inserts nothing.
+  return { event: existing, replayed: true };
+}
+
+/** Key-order-independent serialization: jsonb does not preserve key order. */
+function canonicalJson(value: unknown): string {
+  if (Array.isArray(value)) return `[${value.map(canonicalJson).join(',')}]`;
+  if (value !== null && typeof value === 'object') {
+    const record = value as Record<string, unknown>;
+    const body = Object.keys(record)
+      .sort()
+      .map((key) => `${JSON.stringify(key)}:${canonicalJson(record[key])}`)
+      .join(',');
+    return `{${body}}`;
+  }
+  return JSON.stringify(value);
+}
+
+function sameEvent(row: HierarchyAuditEventRow, input: AppendHierarchyEventInput): boolean {
+  return (
+    row.actorId === input.actorId &&
+    row.verb === input.verb &&
+    row.targetKind === input.targetKind &&
+    row.targetId === input.targetId &&
+    row.correlationId === input.correlationId &&
+    (row.causationId ?? null) === (input.causationId ?? null) &&
+    canonicalJson(row.targetSnapshot) === canonicalJson(input.targetSnapshot)
+  );
+}
+
+/**
+ * Build the immutable snapshot for a node: its row plus the parent chain up
+ * to the company root, root-first, read on the caller's transaction so the
+ * snapshot is consistent with the mutation it audits.
+ */
+export async function buildNodeSnapshot(
+  tx: Tx,
+  kind: HierarchyNodeKind,
+  id: string,
+): Promise<HierarchyNodeSnapshot> {
+  if (kind === 'company') {
+    const rows = await tx.select().from(companies).where(eq(companies.id, id)).limit(1);
+    const row = rows[0];
+    if (!row) throw new HierarchyNodeNotFoundError(kind, id);
+    return { id: row.id, slug: row.slug, name: row.name, parentChain: [] };
+  }
+  if (kind === 'estate') {
+    const rows = await tx.select().from(estates).where(eq(estates.id, id)).limit(1);
+    const row = rows[0];
+    if (!row) throw new HierarchyNodeNotFoundError(kind, id);
+    const parent = await buildNodeSnapshot(tx, 'company', row.companyId);
+    return {
+      id: row.id,
+      slug: row.slug,
+      name: row.name,
+      parentChain: [...parent.parentChain, { kind: 'company', id: parent.id, slug: parent.slug }],
+    };
+  }
+  const rows = await tx.select().from(platformProjects).where(eq(platformProjects.id, id)).limit(1);
+  const row = rows[0];
+  if (!row) throw new HierarchyNodeNotFoundError(kind, id);
+  const parent = await buildNodeSnapshot(tx, 'estate', row.estateId);
+  return {
+    id: row.id,
+    slug: row.slug,
+    name: row.name,
+    parentChain: [...parent.parentChain, { kind: 'estate', id: parent.id, slug: parent.slug }],
+  };
+}
+
+@Injectable()
+export class HierarchyAuditRepository {
+  constructor(@Inject(DB) private readonly db: Db) {}
+
+  /** Compose an event+outbox append into a caller-owned transaction. */
+  append(tx: Tx, input: AppendHierarchyEventInput): Promise<AppendHierarchyEventResult> {
+    return appendHierarchyEvent(tx, input);
+  }
+
+  snapshot(tx: Tx, kind: HierarchyNodeKind, id: string): Promise<HierarchyNodeSnapshot> {
+    return buildNodeSnapshot(tx, kind, id);
+  }
+
+  /** Per-target ordered event history (REQ-AUD-001 per-target ordering; read-only). */
+  async eventsForTarget(targetId: string): Promise<HierarchyAuditEventRow[]> {
+    return this.db
+      .select()
+      .from(hierarchyAuditEvents)
+      .where(eq(hierarchyAuditEvents.targetId, targetId))
+      .orderBy(asc(hierarchyAuditEvents.seq));
+  }
+
+  /**
+   * Claim the oldest pending outbox record (claim-by-CAS: the UPDATE is
+   * guarded on status so a lost race returns null and the caller retries).
+   */
+  async claimPendingOutbox(): Promise<HierarchyOutboxRow | null> {
+    const candidates = await this.db
+      .select()
+      .from(hierarchyOutbox)
+      .where(eq(hierarchyOutbox.status, 'pending'))
+      .orderBy(asc(hierarchyOutbox.createdAt))
+      .limit(1);
+    const candidate = candidates[0];
+    if (!candidate) return null;
+    const claimed = await this.db
+      .update(hierarchyOutbox)
+      .set({ status: 'processing', updatedAt: new Date() })
+      .where(and(eq(hierarchyOutbox.id, candidate.id), eq(hierarchyOutbox.status, 'pending')))
+      .returning();
+    return claimed[0] ?? null;
+  }
+
+  async completeOutbox(id: string): Promise<void> {
+    const now = new Date();
+    await this.db
+      .update(hierarchyOutbox)
+      .set({ status: 'delivered', deliveredAt: now, updatedAt: now })
+      .where(and(eq(hierarchyOutbox.id, id), eq(hierarchyOutbox.status, 'processing')));
+  }
+
+  /** Return a claimed record to pending (delivery failed; it stays replayable). */
+  async releaseOutbox(id: string): Promise<void> {
+    await this.db
+      .update(hierarchyOutbox)
+      .set({ status: 'pending', updatedAt: new Date() })
+      .where(and(eq(hierarchyOutbox.id, id), eq(hierarchyOutbox.status, 'processing')));
+  }
+}

apps/gateway/src/hierarchy/hierarchy.module.ts

@@ -0,0 +1,17 @@
+import { Module } from '@nestjs/common';
+import { HierarchyAuditRepository } from './hierarchy-audit.repository.js';
+
+/**
+ * Hierarchy (tenancy/authorization structure) feature module.
+ *
+ * M4-1b-i ships the audit event + outbox machinery only (contract 1 §5.2).
+ * The hierarchy command family — controllers, DTOs, and the allowlisted
+ * class-table repositories — lands in M4-1b-ii once contract 2 (RBAC grant
+ * model) merges; until then this module exposes no routes, which the
+ * route-inventory witness asserts.
+ */
+@Module({
+  providers: [HierarchyAuditRepository],
+  exports: [HierarchyAuditRepository],
+})
+export class HierarchyModule {}

packages/db/drizzle/0019_volatile_killraven.sql

@@ -0,0 +1,40 @@
+CREATE TYPE "public"."hierarchy_outbox_status" AS ENUM('pending', 'processing', 'delivered');--> statement-breakpoint
+CREATE TABLE "hierarchy_audit_events" (
+	"id" uuid PRIMARY KEY DEFAULT gen_random_uuid() NOT NULL,
+	"seq" bigint GENERATED ALWAYS AS IDENTITY (sequence name "hierarchy_audit_events_seq_seq" INCREMENT BY 1 MINVALUE 1 MAXVALUE 9223372036854775807 START WITH 1 CACHE 1),
+	"actor_id" text NOT NULL,
+	"verb" text NOT NULL,
+	"target_kind" text NOT NULL,
+	"target_id" uuid NOT NULL,
+	"target_snapshot" jsonb NOT NULL,
+	"transfer_from" jsonb,
+	"transfer_to" jsonb,
+	"correlation_id" text NOT NULL,
+	"causation_id" uuid,
+	"idempotency_key" text NOT NULL,
+	"occurred_at" timestamp with time zone DEFAULT now() NOT NULL,
+	CONSTRAINT "hierarchy_audit_events_verb_check" CHECK (verb IN ('create', 'rename', 'transfer', 'delete', 'grant_create', 'grant_change', 'grant_revoke')),
+	CONSTRAINT "hierarchy_audit_events_target_kind_check" CHECK (target_kind IN ('company', 'estate', 'platform_project', 'grant')),
+	CONSTRAINT "hierarchy_audit_events_transfer_check" CHECK ((verb = 'transfer') = (transfer_from IS NOT NULL AND transfer_to IS NOT NULL))
+);
+--> statement-breakpoint
+CREATE TABLE "hierarchy_outbox" (
+	"id" uuid PRIMARY KEY DEFAULT gen_random_uuid() NOT NULL,
+	"event_id" uuid NOT NULL,
+	"idempotency_key" text NOT NULL,
+	"correlation_id" text NOT NULL,
+	"status" "hierarchy_outbox_status" DEFAULT 'pending' NOT NULL,
+	"created_at" timestamp with time zone DEFAULT now() NOT NULL,
+	"updated_at" timestamp with time zone DEFAULT now() NOT NULL,
+	"delivered_at" timestamp with time zone
+);
+--> statement-breakpoint
+ALTER TABLE "hierarchy_audit_events" ADD CONSTRAINT "hierarchy_audit_events_causation_id_hierarchy_audit_events_id_fk" FOREIGN KEY ("causation_id") REFERENCES "public"."hierarchy_audit_events"("id") ON DELETE restrict ON UPDATE no action;--> statement-breakpoint
+ALTER TABLE "hierarchy_outbox" ADD CONSTRAINT "hierarchy_outbox_event_id_hierarchy_audit_events_id_fk" FOREIGN KEY ("event_id") REFERENCES "public"."hierarchy_audit_events"("id") ON DELETE restrict ON UPDATE no action;--> statement-breakpoint
+CREATE UNIQUE INDEX "hierarchy_audit_events_idempotency_idx" ON "hierarchy_audit_events" USING btree ("idempotency_key");--> statement-breakpoint
+CREATE UNIQUE INDEX "hierarchy_audit_events_seq_idx" ON "hierarchy_audit_events" USING btree ("seq");--> statement-breakpoint
+CREATE INDEX "hierarchy_audit_events_target_seq_idx" ON "hierarchy_audit_events" USING btree ("target_id","seq");--> statement-breakpoint
+CREATE INDEX "hierarchy_audit_events_correlation_idx" ON "hierarchy_audit_events" USING btree ("correlation_id");--> statement-breakpoint
+CREATE UNIQUE INDEX "hierarchy_outbox_event_idx" ON "hierarchy_outbox" USING btree ("event_id");--> statement-breakpoint
+CREATE UNIQUE INDEX "hierarchy_outbox_idempotency_idx" ON "hierarchy_outbox" USING btree ("idempotency_key");--> statement-breakpoint
+CREATE INDEX "hierarchy_outbox_status_created_idx" ON "hierarchy_outbox" USING btree ("status","created_at");

packages/db/drizzle/meta/_journal.json

@@ -134,6 +134,13 @@
       "when": 1787862158838,
       "tag": "0018_clean_cobalt_man",
       "breakpoints": true
+    },
+    {
+      "idx": 19,
+      "version": "7",
+      "when": 1787880918208,
+      "tag": "0019_volatile_killraven",
+      "breakpoints": true
     }
   ]
 }

packages/db/src/hierarchy-audit.witness.test.ts

@@ -0,0 +1,363 @@
+/**
+ * Hierarchy audit event + outbox schema witnesses — contract 1 §5.2 and the
+ * schema-level half of §6.4.
+ *
+ * Witnesses the guarantees the tables themselves carry: verb/target-kind/
+ * transfer CHECK constraints, idempotency uniqueness (REQ-AUD-001 duplicate
+ * suppression at the database level), monotonic append order (`seq`),
+ * deletion-safe linkage (no foreign key from the events table into any class
+ * table — events survive the deletion of their target), the causation
+ * self-FK, and the outbox's FK/uniqueness/status shape. The repository-level
+ * half of §6.4 (same-transaction atomicity, rollback, replay) is witnessed in
+ * apps/gateway/src/hierarchy/hierarchy-audit.witness.test.ts.
+ *
+ * Two legs run the same witness body:
+ *  - PGlite (WASM Postgres): always runs.
+ *  - Real PostgreSQL (§6.8): runs when DATABASE_URL is set — the binding
+ *    witness; CI migrates ci-postgres before `pnpm test`.
+ */
+import { randomUUID } from 'node:crypto';
+import { mkdtempSync, rmSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+import { sql } from 'drizzle-orm';
+import { afterAll, beforeAll, describe, expect, it } from 'vitest';
+import { createDb } from './client.js';
+import { createPgliteDb } from './client-pglite.js';
+import { runPgliteMigrations } from './migrate.js';
+import { companies, hierarchyAuditEvents, hierarchyOutbox } from './schema.js';
+
+type AnyDb = {
+  db: {
+    insert: (t: unknown) => { values: (v: unknown) => Promise<unknown> };
+    execute: (q: unknown) => Promise<{ rows?: unknown[] } | unknown[]>;
+  };
+  close: () => Promise<void>;
+};
+
+/** Match a constraint failure anywhere along drizzle's cause chain. */
+async function expectViolation(p: Promise<unknown>, re: RegExp, label = ''): Promise<void> {
+  let err: unknown;
+  try {
+    await p;
+  } catch (e) {
+    err = e;
+  }
+  expect(err, label || 'expected the statement to be refused').toBeDefined();
+  const messages: string[] = [];
+  let cur: unknown = err;
+  while (cur instanceof Error) {
+    messages.push(cur.message);
+    cur = (cur as { cause?: unknown }).cause;
+  }
+  expect(messages.join(' | '), label).toMatch(re);
+}
+
+function rows(res: { rows?: unknown[] } | unknown[]): Record<string, unknown>[] {
+  return (Array.isArray(res) ? res : (res.rows ?? [])) as Record<string, unknown>[];
+}
+
+/** Unique per-run prefix so real-PG runs never collide and clean up safely. */
+const T = `hier-a-${randomUUID().slice(0, 8)}`;
+
+/** Minimal valid event row; overrides compose the negative cases. */
+type EventInsert = typeof hierarchyAuditEvents.$inferInsert;
+
+function eventRow(overrides: Partial<EventInsert> = {}): EventInsert {
+  return {
+    actorId: `${T}-actor`,
+    verb: 'create',
+    targetKind: 'company',
+    targetId: randomUUID(),
+    targetSnapshot: { id: 'x', slug: 'x', name: 'x', parentChain: [] },
+    correlationId: `${T}-corr`,
+    idempotencyKey: `${T}-${randomUUID()}`,
+    ...overrides,
+  };
+}
+
+function witnessSuite(getHandle: () => AnyDb): void {
+  const db = () => getHandle().db as unknown as ReturnType<typeof createDb>['db'];
+
+  afterAll(async () => {
+    const d = db();
+    await d.execute(sql`DELETE FROM hierarchy_outbox WHERE idempotency_key LIKE ${T + '%'}`);
+    // Caused events first: the causation self-FK is RESTRICT.
+    await d.execute(
+      sql`DELETE FROM hierarchy_audit_events WHERE idempotency_key LIKE ${T + '%'} AND causation_id IS NOT NULL`,
+    );
+    await d.execute(sql`DELETE FROM hierarchy_audit_events WHERE idempotency_key LIKE ${T + '%'}`);
+    await d.execute(sql`DELETE FROM companies WHERE slug LIKE ${T + '%'}`);
+  });
+
+  // ── CHECK constraints ──────────────────────────────────────────────────────
+
+  it('accepts every declared verb and refuses an undeclared one', async () => {
+    for (const verb of [
+      'create',
+      'rename',
+      'delete',
+      'grant_create',
+      'grant_change',
+      'grant_revoke',
+    ]) {
+      await db().insert(hierarchyAuditEvents).values(eventRow({ verb }));
+    }
+    await expectViolation(
+      db()
+        .insert(hierarchyAuditEvents)
+        .values(eventRow({ verb: 'update' })),
+      /verb_check|violates check/i,
+      'undeclared verb must be refused',
+    );
+  });
+
+  it('refuses an undeclared target kind', async () => {
+    await expectViolation(
+      db()
+        .insert(hierarchyAuditEvents)
+        .values(eventRow({ targetKind: 'workspace' })),
+      /target_kind_check|violates check/i,
+      'workspace is not an audited target kind (workspace mutation is SOT-side)',
+    );
+  });
+
+  it('requires transfer snapshots exactly on transfers', async () => {
+    const parent = { kind: 'company', id: randomUUID(), slug: 'p' };
+    await db()
+      .insert(hierarchyAuditEvents)
+      .values(
+        eventRow({
+          verb: 'transfer',
+          targetKind: 'estate',
+          transferFrom: parent,
+          transferTo: { ...parent, id: randomUUID() },
+        }),
+      );
+    await expectViolation(
+      db()
+        .insert(hierarchyAuditEvents)
+        .values(eventRow({ verb: 'transfer' })),
+      /transfer_check|violates check/i,
+      'transfer without source/destination snapshots must be refused',
+    );
+    await expectViolation(
+      db()
+        .insert(hierarchyAuditEvents)
+        .values(eventRow({ verb: 'transfer', transferFrom: parent })),
+      /transfer_check|violates check/i,
+      'transfer with only the source snapshot must be refused',
+    );
+    await expectViolation(
+      db()
+        .insert(hierarchyAuditEvents)
+        .values(eventRow({ verb: 'create', transferFrom: parent, transferTo: parent })),
+      /transfer_check|violates check/i,
+      'non-transfer with transfer snapshots must be refused',
+    );
+  });
+
+  // ── Idempotency and ordering ───────────────────────────────────────────────
+
+  it('refuses a duplicate idempotency key', async () => {
+    const key = `${T}-dup-${randomUUID()}`;
+    await db()
+      .insert(hierarchyAuditEvents)
+      .values(eventRow({ idempotencyKey: key }));
+    await expectViolation(
+      db()
+        .insert(hierarchyAuditEvents)
+        .values(eventRow({ idempotencyKey: key })),
+      /duplicate key|unique/i,
+    );
+  });
+
+  it('assigns strictly increasing seq in insert order for one target', async () => {
+    const targetId = randomUUID();
+    const k1 = `${T}-seq-1-${randomUUID()}`;
+    const k2 = `${T}-seq-2-${randomUUID()}`;
+    await db()
+      .insert(hierarchyAuditEvents)
+      .values(eventRow({ targetId, idempotencyKey: k1 }));
+    await db()
+      .insert(hierarchyAuditEvents)
+      .values(eventRow({ targetId, verb: 'rename', idempotencyKey: k2 }));
+    const res = rows(
+      await db().execute(
+        sql`SELECT idempotency_key, seq FROM hierarchy_audit_events WHERE target_id = ${targetId} ORDER BY seq ASC`,
+      ),
+    );
+    expect(res.map((r) => r['idempotency_key'])).toEqual([k1, k2]);
+    expect(Number(res[1]!['seq'])).toBeGreaterThan(Number(res[0]!['seq']));
+  });
+
+  // ── Deletion-safe linkage (§5.2) ───────────────────────────────────────────
+
+  it('has no foreign key into any class table, and events survive target deletion', async () => {
+    const fks = rows(
+      await db().execute(sql`
+        SELECT ccu.table_name AS referenced_table
+        FROM information_schema.table_constraints tc
+        JOIN information_schema.constraint_column_usage ccu
+          ON ccu.constraint_name = tc.constraint_name AND ccu.constraint_schema = tc.constraint_schema
+        WHERE tc.constraint_type = 'FOREIGN KEY' AND tc.table_name = 'hierarchy_audit_events'
+      `),
+    );
+    // The causation self-FK is the ONLY foreign key on the events table.
+    expect([...new Set(fks.map((r) => r['referenced_table']))]).toEqual(['hierarchy_audit_events']);
+
+    const companyId = randomUUID();
+    await db()
+      .insert(companies)
+      .values({ id: companyId, name: 'Doomed', slug: `${T}-doomed` });
+    const key = `${T}-survive-${randomUUID()}`;
+    await db()
+      .insert(hierarchyAuditEvents)
+      .values(
+        eventRow({
+          verb: 'delete',
+          targetId: companyId,
+          targetSnapshot: { id: companyId, slug: `${T}-doomed`, name: 'Doomed', parentChain: [] },
+          idempotencyKey: key,
+        }),
+      );
+    await db().execute(sql`DELETE FROM companies WHERE id = ${companyId}`);
+    const after = rows(
+      await db().execute(
+        sql`SELECT target_snapshot FROM hierarchy_audit_events WHERE idempotency_key = ${key}`,
+      ),
+    );
+    expect(after).toHaveLength(1);
+    expect((after[0]!['target_snapshot'] as { id: string }).id).toBe(companyId);
+  });
+
+  it('enforces the causation self-FK and RESTRICTs deleting a cause', async () => {
+    await expectViolation(
+      db()
+        .insert(hierarchyAuditEvents)
+        .values(eventRow({ causationId: randomUUID() })),
+      /foreign key/i,
+      'causation must reference an existing event',
+    );
+    const causeKey = `${T}-cause-${randomUUID()}`;
+    await db()
+      .insert(hierarchyAuditEvents)
+      .values(eventRow({ verb: 'delete', idempotencyKey: causeKey }));
+    const cause = rows(
+      await db().execute(
+        sql`SELECT id FROM hierarchy_audit_events WHERE idempotency_key = ${causeKey}`,
+      ),
+    )[0]!;
+    await db()
+      .insert(hierarchyAuditEvents)
+      .values(
+        eventRow({ verb: 'grant_revoke', targetKind: 'grant', causationId: cause['id'] as string }),
+      );
+    await expectViolation(
+      db().execute(sql`DELETE FROM hierarchy_audit_events WHERE id = ${cause['id'] as string}`),
+      /foreign key/i,
+      'a cause with dependent events must not be deletable',
+    );
+  });
+
+  // ── Outbox shape ───────────────────────────────────────────────────────────
+
+  it('outbox rows require an existing event, one outbox row per event, unique idempotency', async () => {
+    await expectViolation(
+      db()
+        .insert(hierarchyOutbox)
+        .values({
+          eventId: randomUUID(),
+          idempotencyKey: `${T}-ob-${randomUUID()}`,
+          correlationId: `${T}-corr`,
+        }),
+      /foreign key/i,
+      'outbox must reference an existing event',
+    );
+    const key = `${T}-ob-${randomUUID()}`;
+    await db()
+      .insert(hierarchyAuditEvents)
+      .values(eventRow({ idempotencyKey: key }));
+    const event = rows(
+      await db().execute(sql`SELECT id FROM hierarchy_audit_events WHERE idempotency_key = ${key}`),
+    )[0]!;
+    const eventId = event['id'] as string;
+    await db()
+      .insert(hierarchyOutbox)
+      .values({ eventId, idempotencyKey: key, correlationId: `${T}-corr` });
+    await expectViolation(
+      db()
+        .insert(hierarchyOutbox)
+        .values({ eventId, idempotencyKey: `${T}-ob2-${randomUUID()}`, correlationId: `${T}-c` }),
+      /duplicate key|unique/i,
+      'one outbox record per event',
+    );
+    await expectViolation(
+      db().execute(
+        sql`INSERT INTO hierarchy_outbox (event_id, idempotency_key, correlation_id, status)
+            VALUES (${eventId}, ${`${T}-ob3-${randomUUID()}`}, 'c', 'failed')`,
+      ),
+      /invalid input value for enum|22P02/i,
+      'status outside pending/processing/delivered must be refused',
+    );
+  });
+
+  it('outbox FK RESTRICTs event deletion while the outbox row exists', async () => {
+    const key = `${T}-obr-${randomUUID()}`;
+    await db()
+      .insert(hierarchyAuditEvents)
+      .values(eventRow({ idempotencyKey: key }));
+    const event = rows(
+      await db().execute(sql`SELECT id FROM hierarchy_audit_events WHERE idempotency_key = ${key}`),
+    )[0]!;
+    await db()
+      .insert(hierarchyOutbox)
+      .values({
+        eventId: event['id'] as string,
+        idempotencyKey: key,
+        correlationId: `${T}-corr`,
+      });
+    await expectViolation(
+      db().execute(sql`DELETE FROM hierarchy_audit_events WHERE id = ${event['id'] as string}`),
+      /foreign key/i,
+    );
+  });
+}
+
+// ── Leg 1: PGlite (always runs — local witness signal) ───────────────────────
+
+describe('hierarchy audit witnesses — PGlite', () => {
+  let dir: string;
+  let handle: ReturnType<typeof createPgliteDb>;
+
+  beforeAll(async () => {
+    dir = mkdtempSync(join(tmpdir(), 'hier-audit-witness-'));
+    handle = createPgliteDb(dir);
+    await runPgliteMigrations(handle);
+  });
+
+  afterAll(async () => {
+    await handle.close();
+    rmSync(dir, { recursive: true, force: true });
+  });
+
+  witnessSuite(() => handle as unknown as AnyDb);
+});
+
+// ── Leg 2: real PostgreSQL (§6.8 — binding witness, ci-postgres in CI) ───────
+
+const hasPostgres = Boolean(process.env['DATABASE_URL']);
+
+describe.skipIf(!hasPostgres)('hierarchy audit witnesses — real PostgreSQL', () => {
+  let handle: ReturnType<typeof createDb>;
+
+  beforeAll(() => {
+    handle = createDb(process.env['DATABASE_URL']!);
+  });
+
+  afterAll(async () => {
+    await handle.close();
+  });
+
+  witnessSuite(() => handle as unknown as AnyDb);
+});

packages/db/src/hierarchy-writer-coverage.test.ts

@@ -123,18 +123,20 @@
  *     tracked for M4-1b consideration); the counterfactual — flagging every
  *     bare identifier call — false-positives on essentially all callback
  *     code. Reviews of modules touching db handles carry this residual.
- *   - The scan perimeter is <root>/<pkg>/src for the three roots; production
- *     TS outside a src/ directory (e.g. packages/mosaic/framework/**) is not
- *     scanned (verified free of db/driver/execute references at review time).
- *     Files excluded from the scan — test files and out-of-src modules — are
- *     also invisible as import-graph CONDUITS: test files are emitted to
- *     dist, so a production module could launder a symbol or capability
- *     through a re-export in one. Importing a test module from production
- *     code is anomalous and review-visible; the blind spot is accepted as a
- *     residual, not closed.
+ *   - The scan perimeter is the full <root>/<pkg> tree for the three roots
+ *     (build output, tool caches, and dot-directories excluded), so
+ *     production TS outside src/ — package configs, e2e helpers,
+ *     packages/mosaic/framework/** — is scanned and conduit-visible
+ *     (widened from src/-only in M4-1b-i; the widened set was measured free
+ *     of every trigger token at the time). Files excluded from the scan —
+ *     test files — are still invisible as import-graph CONDUITS: test files
+ *     are emitted to dist, so a production module could launder a symbol or
+ *     capability through a re-export in one. Importing a test module from
+ *     production code is anomalous and review-visible; that blind spot is
+ *     accepted as a residual, not closed.
  *
  * The writer allowlist names hierarchy command/repository modules ONLY. It is
- * empty today: the hierarchy command family (M4-1b) has not landed, so no
+ * empty today: the hierarchy command family (M4-1b-ii) has not landed, so no
  * production module may write the class tables. The infrastructure register
  * holds legitimate non-hierarchy raw execution; registered modules are exempt
  * from prong (iii) only — prongs (i) and (ii) apply to them with no
@@ -179,7 +181,8 @@ const CLASS_TABLES = [
 
 /**
  * Writer allowlist (§6.3b): hierarchy command/repository modules only.
- * EMPTY until the hierarchy command family lands (M4-1b). Adding a module
+ * EMPTY until the hierarchy command family lands (M4-1b-ii; M4-1b-i ships
+ * only the audit/outbox machinery, which writes no class table). Adding a module
  * here is a contract-conformance decision reviewed under §5.1 — the module
  * must be part of the Gateway hierarchy command path, and it must not export
  * a function that executes caller-supplied SQL.
@@ -291,20 +294,23 @@ function isTestPath(rel: string): boolean {
   );
 }
 
+/** Directory names excluded from the walk: build output and tool caches only. */
+const EXCLUDED_DIRS = new Set(['node_modules', 'dist', 'build', 'coverage', 'test-results']);
+
 function collectSources(): string[] {
   const files: string[] = [];
   for (const root of SCAN_ROOTS) {
     const rootDir = join(REPO_ROOT, root);
     if (!existsSync(rootDir)) continue;
     for (const pkg of readdirSync(rootDir)) {
-      const srcDir = join(rootDir, pkg, 'src');
-      if (!existsSync(srcDir) || !statSync(srcDir).isDirectory()) continue;
+      const pkgDir = join(rootDir, pkg);
+      if (!statSync(pkgDir).isDirectory()) continue;
       const walk = (dir: string): void => {
         for (const entry of readdirSync(dir)) {
           const full = join(dir, entry);
           const st = statSync(full);
           if (st.isDirectory()) {
-            if (entry === 'node_modules' || entry === 'dist') continue;
+            if (EXCLUDED_DIRS.has(entry) || entry.startsWith('.')) continue;
             walk(full);
           } else if (EXTENSIONS.has(full.slice(full.lastIndexOf('.')))) {
             const rel = relative(REPO_ROOT, full).split(sep).join('/');
@@ -312,7 +318,7 @@ function collectSources(): string[] {
           }
         }
       };
-      walk(srcDir);
+      walk(pkgDir);
     }
   }
   return files.sort();

packages/db/src/schema.ts

@@ -4,6 +4,7 @@
  */
 
 import { sql } from 'drizzle-orm';
+import type { AnyPgColumn } from 'drizzle-orm/pg-core';
 import {
   pgTable,
   pgEnum,
@@ -1152,3 +1153,111 @@ export const hierarchyGrants = pgTable(
     index('hierarchy_grants_granted_by_idx').on(t.grantedBy),
   ],
 );
+
+// ─── Hierarchy audit events + outbox (contract 1 §5.2) ──────────────────────
+// NOT part of the record class (the class is exactly the five tables above).
+// Append-only semantic audit log for hierarchy mutations, with a dedicated
+// transactional outbox — hierarchy events are not workspace-scoped rows and
+// do not ride the workspace outbox. Deletion-safe linkage: events reference
+// their target by an immutable snapshot (id, slug, parent chain at event
+// time), never by a foreign key into the class tables, so append-only events
+// survive the deletion of their target. Append-only is enforced at the
+// application layer (the hierarchy audit repository exposes no update/delete
+// path for events); REQ-AUD-001's INSERT/SELECT-only database role is a
+// deployment concern outside this schema.
+
+export const HIERARCHY_AUDIT_VERBS = [
+  'create',
+  'rename',
+  'transfer',
+  'delete',
+  'grant_create',
+  'grant_change',
+  'grant_revoke',
+] as const;
+
+export const HIERARCHY_AUDIT_TARGET_KINDS = [
+  'company',
+  'estate',
+  'platform_project',
+  'grant',
+] as const;
+
+export const hierarchyAuditEvents = pgTable(
+  'hierarchy_audit_events',
+  {
+    id: uuid('id').primaryKey().defaultRandom(),
+    // Global append order; per-target ordering (REQ-AUD-001) is a filter on
+    // target_id ordered by seq.
+    seq: bigint('seq', { mode: 'number' }).notNull().generatedAlwaysAsIdentity(),
+    // No FK: audit events outlive every principal and every target (§5.2).
+    actorId: text('actor_id').notNull(),
+    verb: text('verb').notNull(),
+    targetKind: text('target_kind').notNull(),
+    targetId: uuid('target_id').notNull(),
+    // Immutable snapshot at event time. Node events: { id, slug, name,
+    // parentChain: [{ kind, id, slug }, …] root-first }. Grant events:
+    // { id, subject: { userId | teamId }, target: { kind, id }, role }
+    // (subject and role per contract 2 §4.4).
+    targetSnapshot: jsonb('target_snapshot').notNull(),
+    // Present exactly on transfers: snapshot of the source/destination
+    // parent ({ kind, id, slug }), CHECK-enforced below.
+    transferFrom: jsonb('transfer_from'),
+    transferTo: jsonb('transfer_to'),
+    correlationId: text('correlation_id').notNull(),
+    // Prior event in the causal chain (e.g. cascaded grant_revoke events
+    // caused by a node delete). Self-FK RESTRICT keeps the chain intact.
+    causationId: uuid('causation_id').references((): AnyPgColumn => hierarchyAuditEvents.id, {
+      onDelete: 'restrict',
+    }),
+    idempotencyKey: text('idempotency_key').notNull(),
+    occurredAt: timestamp('occurred_at', { withTimezone: true }).notNull().defaultNow(),
+  },
+  (t) => [
+    uniqueIndex('hierarchy_audit_events_idempotency_idx').on(t.idempotencyKey),
+    uniqueIndex('hierarchy_audit_events_seq_idx').on(t.seq),
+    index('hierarchy_audit_events_target_seq_idx').on(t.targetId, t.seq),
+    index('hierarchy_audit_events_correlation_idx').on(t.correlationId),
+    check(
+      'hierarchy_audit_events_verb_check',
+      sql`verb IN ('create', 'rename', 'transfer', 'delete', 'grant_create', 'grant_change', 'grant_revoke')`,
+    ),
+    check(
+      'hierarchy_audit_events_target_kind_check',
+      sql`target_kind IN ('company', 'estate', 'platform_project', 'grant')`,
+    ),
+    check(
+      'hierarchy_audit_events_transfer_check',
+      sql`(verb = 'transfer') = (transfer_from IS NOT NULL AND transfer_to IS NOT NULL)`,
+    ),
+  ],
+);
+
+export const hierarchyOutboxStatusEnum = pgEnum('hierarchy_outbox_status', [
+  'pending',
+  'processing',
+  'delivered',
+]);
+
+export const hierarchyOutbox = pgTable(
+  'hierarchy_outbox',
+  {
+    id: uuid('id').primaryKey().defaultRandom(),
+    // FK into the append-only events table (not a class table): never
+    // dangles, so RESTRICT is safe and keeps event/outbox integrity.
+    eventId: uuid('event_id')
+      .notNull()
+      .references(() => hierarchyAuditEvents.id, { onDelete: 'restrict' }),
+    idempotencyKey: text('idempotency_key').notNull(),
+    correlationId: text('correlation_id').notNull(),
+    status: hierarchyOutboxStatusEnum('status').notNull().default('pending'),
+    createdAt: timestamp('created_at', { withTimezone: true }).notNull().defaultNow(),
+    updatedAt: timestamp('updated_at', { withTimezone: true }).notNull().defaultNow(),
+    deliveredAt: timestamp('delivered_at', { withTimezone: true }),
+  },
+  (t) => [
+    uniqueIndex('hierarchy_outbox_event_idx').on(t.eventId),
+    uniqueIndex('hierarchy_outbox_idempotency_idx').on(t.idempotencyKey),
+    index('hierarchy_outbox_status_created_idx').on(t.status, t.createdAt),
+  ],
+);