diff --git a/packages/iios-contracts/src/events.ts b/packages/iios-contracts/src/events.ts
index 4c78d27..713d509 100644
--- a/packages/iios-contracts/src/events.ts
+++ b/packages/iios-contracts/src/events.ts
@@ -52,6 +52,7 @@ export const IIOS_EVENTS = {
   meetingSummarized: 'com.insignia.iios.calendar.meeting.summarized.v1',
   notificationQueued: 'com.insignia.iios.notification.queued.v1',
   deliveryAttempted: 'com.insignia.iios.delivery.attempted.v1',
+  devChaos: 'com.insignia.iios.dev.chaos.v1',
 } as const;
 
 export type IiosEventType = (typeof IIOS_EVENTS)[keyof typeof IIOS_EVENTS];
diff --git a/packages/iios-service/scripts/smoke-dlq.mjs b/packages/iios-service/scripts/smoke-dlq.mjs
new file mode 100644
index 0000000..b68863b
--- /dev/null
+++ b/packages/iios-service/scripts/smoke-dlq.mjs
@@ -0,0 +1,71 @@
+// P9 slice-5 DLQ smoke: a poison chaos event is dead-lettered (not lost), shows up
+// tenant-scoped in /v1/dlq, another tenant can neither see nor replay it, and the
+// owner's replay resolves it (KG-13 / KG-06). Requires the service running with
+// IIOS_DEV_TOKENS=1 (the relay ticks by default, publishing the poison to the consumer).
+import 'dotenv/config';
+
+const SERVICE = process.env.SMOKE_URL ?? 'http://localhost:3200';
+const APP_ID = 'portal-demo';
+const assert = (c, m) => { if (!c) { console.error('✗', m); process.exit(1); } console.log('✓', m); };
+const sleep = (ms) => new Promise((r) => setTimeout(r, ms));
+
+async function devToken(userId, orgId) {
+  const r = await fetch(`${SERVICE}/v1/dev/token`, {
+    method: 'POST',
+    headers: { 'content-type': 'application/json' },
+    body: JSON.stringify({ appId: APP_ID, userId, name: userId, orgId }),
+  });
+  if (!r.ok) throw new Error(`devToken ${r.status} (service with IIOS_DEV_TOKENS=1?)`);
+  return (await r.json()).token;
+}
+async function call(token, path, method = 'GET', body) {
+  return fetch(`${SERVICE}${path}`, {
+    method,
+    headers: { 'content-type': 'application/json', authorization: `Bearer ${token}` },
+    body: body ? JSON.stringify(body) : undefined,
+  });
+}
+async function json(token, path, method = 'GET', body) {
+  const r = await call(token, path, method, body);
+  if (!r.ok) throw new Error(`${method} ${path} ${r.status}: ${await r.text()}`);
+  return r.json();
+}
+
+const A = await devToken('a1', 'org_A');
+const B = await devToken('b1', 'org_B');
+
+// A injects a poison chaos event.
+const { eventId } = await json(A, '/v1/dev/chaos/poison', 'POST');
+assert(eventId.startsWith('evt_chaos_'), `A injected a poison chaos event (${eventId})`);
+
+// Poll until the relay publishes it and the chaos consumer dead-letters it.
+let item;
+for (let i = 0; i < 40; i++) {
+  const list = await json(A, '/v1/dlq');
+  item = list.find((d) => d.sourceId === eventId);
+  if (item) break;
+  await sleep(250);
+}
+assert(item, 'poison surfaced in A\'s DLQ (relay published → consumer failed → dead-lettered)');
+assert(item.status === 'QUARANTINED', `DLQ item is QUARANTINED (got ${item.status})`);
+assert(item.consumerName === 'chaos-consumer', `dead-lettered by the chaos-consumer lane (got ${item.consumerName})`);
+
+// Tenant B cannot see A's DLQ item.
+const bList = await json(B, '/v1/dlq');
+assert(!bList.some((d) => d.sourceId === eventId), "tenant B's DLQ excludes A's item (isolation)");
+
+// Tenant B cannot replay A's DLQ item.
+const bReplay = await call(B, `/v1/dlq/${item.id}/replay`, 'POST');
+assert(bReplay.status === 403, `tenant B replaying A's item → 403 (got ${bReplay.status}) — KG-02`);
+
+// A replays → resolves.
+const replayed = await json(A, `/v1/dlq/${item.id}/replay`, 'POST');
+assert(replayed.status === 'RESOLVED', `A's replay resolves the poison (got ${replayed.status})`);
+
+// It now shows RESOLVED in A's DLQ.
+const afterList = await json(A, '/v1/dlq');
+const after = afterList.find((d) => d.sourceId === eventId);
+assert(after && after.status === 'RESOLVED', 'DLQ item is RESOLVED after replay');
+
+console.log('\nP9 DLQ smoke: PASS');
+process.exit(0);
diff --git a/packages/iios-service/src/dev/dev.controller.ts b/packages/iios-service/src/dev/dev.controller.ts
index 764a310..a1ebd25 100644
--- a/packages/iios-service/src/dev/dev.controller.ts
+++ b/packages/iios-service/src/dev/dev.controller.ts
@@ -1,9 +1,13 @@
 import { randomUUID } from 'node:crypto';
-import { BadRequestException, Body, Controller, ForbiddenException, Param, Post } from '@nestjs/common';
+import { BadRequestException, Body, Controller, ForbiddenException, Headers, Param, Post } from '@nestjs/common';
 import jwt from 'jsonwebtoken';
+import { IIOS_EVENTS } from '@insignia/iios-contracts';
 import { hmacSign } from '@insignia/iios-adapter-sdk';
 import { InboundService } from '../adapters/inbound.service';
 import { AdapterRegistry } from '../adapters/adapter.registry';
+import { PrismaService } from '../prisma/prisma.service';
+import { ActorResolver, type MessagePrincipal } from '../identity/actor.resolver';
+import { SessionVerifier } from '../platform/session.verifier';
 
 /**
  * Dev-only helpers (gated by IIOS_DEV_TOKENS=1). Never enable in production.
@@ -13,6 +17,9 @@ export class DevController {
   constructor(
     private readonly inbound: InboundService,
     private readonly registry: AdapterRegistry,
+    private readonly prisma: PrismaService,
+    private readonly actors: ActorResolver,
+    private readonly session: SessionVerifier,
   ) {}
 
   @Post('token')
@@ -55,6 +62,46 @@ export class DevController {
     });
   }
 
+  /**
+   * Inject a poison chaos event into the outbox. The relay publishes it, the
+   * ChaosConsumer throws on first delivery → it is dead-lettered under the caller's
+   * scope, then `POST /v1/dlq/:id/replay` resolves it. Drives the DLQ smoke.
+   */
+  @Post('chaos/poison')
+  async poison(@Headers('authorization') auth?: string): Promise<{ eventId: string; scopeId: string }> {
+    this.assertDev();
+    const principal = this.principal(auth);
+    const scope = await this.actors.resolveScope(principal); // find-or-create so GET /v1/dlq matches
+    const id = `evt_chaos_${randomUUID()}`;
+    const cloudEvent = {
+      specversion: '1.0',
+      id,
+      type: IIOS_EVENTS.devChaos,
+      source: `iios/dev/${principal.appId}`,
+      subject: `chaos/${id}`,
+      time: new Date().toISOString(),
+      datacontenttype: 'application/json',
+      insignia: { scopeSnapshotId: scope.id, idempotencyKey: id, dataClass: 'internal' },
+      data: { poison: true },
+    };
+    await this.prisma.iiosOutboxEvent.create({
+      data: {
+        aggregateType: 'dev-chaos',
+        aggregateId: id,
+        eventType: IIOS_EVENTS.devChaos,
+        cloudEvent: cloudEvent as unknown as object,
+        partitionKey: `${principal.orgId}:${principal.appId}:chaos`,
+      },
+    });
+    return { eventId: id, scopeId: scope.id };
+  }
+
+  private principal(authorization?: string): MessagePrincipal {
+    const token = (authorization ?? '').replace(/^Bearer\s+/i, '');
+    if (!token) throw new BadRequestException('Authorization bearer token is required');
+    return this.session.verify(token);
+  }
+
   private assertDev(): void {
     if (process.env.IIOS_DEV_TOKENS !== '1') throw new ForbiddenException('dev endpoints disabled');
   }
diff --git a/packages/iios-service/src/outbox/chaos.consumer.ts b/packages/iios-service/src/outbox/chaos.consumer.ts
new file mode 100644
index 0000000..fb634e7
--- /dev/null
+++ b/packages/iios-service/src/outbox/chaos.consumer.ts
@@ -0,0 +1,45 @@
+import { Injectable, OnModuleInit } from '@nestjs/common';
+import { CloudEvent, IIOS_EVENTS } from '@insignia/iios-contracts';
+import { PrismaService } from '../prisma/prisma.service';
+import { OutboxBus } from './outbox.bus';
+import { DlqService } from './dlq.service';
+
+/**
+ * Dev-only chaos consumer (P9). Drives the DLQ smoke deterministically: it THROWS on
+ * the first delivery of a chaos event (so the event is dead-lettered) and SUCCEEDS on
+ * replay (so the DLQ item resolves). Registered like any projector — same claim() +
+ * onConsumerFailure wiring — so it exercises the real dead-letter/replay path.
+ */
+@Injectable()
+export class ChaosConsumer implements OnModuleInit {
+  private readonly consumer = 'chaos-consumer';
+  private readonly seen = new Set<string>();
+
+  constructor(
+    private readonly prisma: PrismaService,
+    private readonly bus: OutboxBus,
+    private readonly dlq: DlqService,
+  ) {}
+
+  onModuleInit(): void {
+    this.dlq.registerHandler(this.consumer, (e) => this.onChaos(e));
+    this.bus.on(IIOS_EVENTS.devChaos, (p) => void this.onChaos(p as CloudEvent).catch((err) => this.dlq.onConsumerFailure(this.consumer, p as CloudEvent, err)));
+  }
+
+  async onChaos(event: CloudEvent): Promise<void> {
+    if (!(await this.claim(event.id))) return; // idempotent
+    if (!this.seen.has(event.id)) {
+      this.seen.add(event.id);
+      throw new Error('chaos: first delivery always fails'); // → dead-lettered, claim cleared
+    }
+    // replay: succeeds (the claim persists, marking it processed exactly-once)
+  }
+
+  private async claim(eventId: string): Promise<boolean> {
+    const res = await this.prisma.iiosProcessedEvent.createMany({
+      data: [{ consumerName: this.consumer, eventId }],
+      skipDuplicates: true,
+    });
+    return res.count > 0;
+  }
+}
diff --git a/packages/iios-service/src/outbox/dlq.controller.ts b/packages/iios-service/src/outbox/dlq.controller.ts
new file mode 100644
index 0000000..de48ae2
--- /dev/null
+++ b/packages/iios-service/src/outbox/dlq.controller.ts
@@ -0,0 +1,46 @@
+import { BadRequestException, Controller, ForbiddenException, Get, Headers, NotFoundException, Param, Post, Query } from '@nestjs/common';
+import { PrismaService } from '../prisma/prisma.service';
+import { ActorResolver, type MessagePrincipal } from '../identity/actor.resolver';
+import { SessionVerifier } from '../platform/session.verifier';
+import { recordAudit } from '../observability/audit';
+import { DlqService } from './dlq.service';
+
+/**
+ * DLQ ops surface (P9, KG-13). Strictly tenant-scoped: a caller only ever sees and
+ * replays dead-letters owned by their own scope (assertOwns fences replay by id).
+ */
+@Controller('v1/dlq')
+export class DlqController {
+  constructor(
+    private readonly prisma: PrismaService,
+    private readonly dlq: DlqService,
+    private readonly actors: ActorResolver,
+    private readonly session: SessionVerifier,
+  ) {}
+
+  @Get()
+  async list(@Query('status') status?: string, @Headers('authorization') auth?: string) {
+    const principal = this.principal(auth);
+    const scope = await this.actors.findScope(principal);
+    if (!scope) return []; // a caller with no scope owns nothing
+    return this.dlq.listDlq(scope.id, status);
+  }
+
+  @Post(':id/replay')
+  async replay(@Param('id') id: string, @Headers('authorization') auth?: string) {
+    const principal = this.principal(auth);
+    const item = await this.prisma.iiosDlqItem.findUnique({ where: { id } });
+    if (!item) throw new NotFoundException('dlq item not found');
+    if (!item.scopeId) throw new ForbiddenException('dlq item is not tenant-scoped');
+    const scope = await this.actors.assertOwns(principal, item.scopeId); // KG-02 fence
+    const result = await this.dlq.replay(id);
+    await recordAudit(this.prisma, { action: 'dlq.replay', resourceType: 'dlq_item', resourceId: id, scopeId: scope.id });
+    return result;
+  }
+
+  private principal(authorization?: string): MessagePrincipal {
+    const token = (authorization ?? '').replace(/^Bearer\s+/i, '');
+    if (!token) throw new BadRequestException('Authorization bearer token is required');
+    return this.session.verify(token);
+  }
+}
diff --git a/packages/iios-service/src/outbox/outbox.module.ts b/packages/iios-service/src/outbox/outbox.module.ts
index e68547e..5158a4f 100644
--- a/packages/iios-service/src/outbox/outbox.module.ts
+++ b/packages/iios-service/src/outbox/outbox.module.ts
@@ -2,9 +2,12 @@ import { Module } from '@nestjs/common';
 import { OutboxBus } from './outbox.bus';
 import { OutboxRelay } from './outbox.relay';
 import { DlqService } from './dlq.service';
+import { DlqController } from './dlq.controller';
+import { ChaosConsumer } from './chaos.consumer';
 
 @Module({
-  providers: [OutboxBus, OutboxRelay, DlqService],
+  controllers: [DlqController],
+  providers: [OutboxBus, OutboxRelay, DlqService, ChaosConsumer],
   exports: [OutboxBus, OutboxRelay, DlqService],
 })
 export class OutboxModule {}