feat(hierarchy): audit event + outbox machinery (M4-1b-i, contract 1 §5.2) (#1460)

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 +1,247 @@
+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('throws on a duplicate idempotency key whose transfer destination differs', async () => {
+    const from = { kind: 'company' as const, id: randomUUID(), slug: 'src-co' };
+    const to = { kind: 'company' as const, id: randomUUID(), slug: 'dst-co' };
+    const first = input({
+      verb: 'transfer',
+      targetKind: 'estate',
+      transferFrom: from,
+      transferTo: to,
+    });
+    const original = await handle.db.transaction(async (tx) => repo.append(tx, first));
+    expect(original.replayed).toBe(false);
+    // Identical retry replays; a retry re-routed to a different destination must conflict.
+    const replay = await handle.db.transaction(async (tx) => repo.append(tx, first));
+    expect(replay.replayed).toBe(true);
+    await expect(
+      handle.db.transaction(async (tx) =>
+        repo.append(tx, { ...first, transferTo: { ...to, id: 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 +1,274 @@
+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) &&
+    // Transfer source/destination are semantic content (§5.2): a retry with a
+    // different destination must conflict, never silently replay.
+    canonicalJson(row.transferFrom ?? null) === canonicalJson(input.transferFrom ?? null) &&
+    canonicalJson(row.transferTo ?? null) === canonicalJson(input.transferTo ?? null)
+  );
+}
+
+/**
+ * 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 {}