diff --git a/packages/iios-service/src/support/assignment.spec.ts b/packages/iios-service/src/support/assignment.spec.ts
index 5f08262..8a4b7ea 100644
--- a/packages/iios-service/src/support/assignment.spec.ts
+++ b/packages/iios-service/src/support/assignment.spec.ts
@@ -5,6 +5,7 @@ import { makeFakePorts } from '@insignia/iios-testkit';
 import { IIOS_EVENTS, type CloudEvent } from '@insignia/iios-contracts';
 import { MessageService, type MessagePrincipal } from '../messaging/message.service';
 import { SupportService } from './support.service';
+import { IdempotencyService } from '../idempotency/idempotency.service';
 import { AssignmentService } from './assignment.service';
 import { ActorResolver } from '../identity/actor.resolver';
 import { OutboxBus } from '../outbox/outbox.bus';
@@ -14,7 +15,7 @@ const url = process.env.DATABASE_URL ?? 'postgresql://iios:iios@localhost:5434/i
 const prisma = new PrismaClient({ datasources: { db: { url } } });
 const asService = prisma as unknown as PrismaService;
 const actors = new ActorResolver(asService);
-const support = () => new SupportService(asService, makeFakePorts(), actors);
+const support = () => new SupportService(asService, makeFakePorts(), actors, new IdempotencyService(asService));
 const assignment = () => new AssignmentService(asService, new OutboxBus(), actors);
 const msg = () => new MessageService(asService, makeFakePorts(), actors);
 
diff --git a/packages/iios-service/src/support/support.controller.ts b/packages/iios-service/src/support/support.controller.ts
index f711e97..aeb51ba 100644
--- a/packages/iios-service/src/support/support.controller.ts
+++ b/packages/iios-service/src/support/support.controller.ts
@@ -22,8 +22,12 @@ export class SupportController {
   ) {}
 
   @Post('tickets')
-  async createTicket(@Body() body: CreateTicketDto, @Headers('authorization') auth?: string) {
-    return this.support.createTicket(this.principal(auth), body);
+  async createTicket(
+    @Body() body: CreateTicketDto,
+    @Headers('idempotency-key') idempotencyKey?: string,
+    @Headers('authorization') auth?: string,
+  ) {
+    return this.support.createTicket(this.principal(auth), body, idempotencyKey);
   }
 
   @Post('escalate')
@@ -42,13 +46,21 @@ export class SupportController {
   }
 
   @Post('callbacks')
-  async callback(@Body() body: CallbackDto, @Headers('authorization') auth?: string) {
-    return this.support.requestCallback(this.principal(auth), {
-      preferChannel: body.preferChannel,
-      preferredTime: body.preferredTime ? new Date(body.preferredTime) : undefined,
-      notes: body.notes,
-      ticketId: body.ticketId,
-    });
+  async callback(
+    @Body() body: CallbackDto,
+    @Headers('idempotency-key') idempotencyKey?: string,
+    @Headers('authorization') auth?: string,
+  ) {
+    return this.support.requestCallback(
+      this.principal(auth),
+      {
+        preferChannel: body.preferChannel,
+        preferredTime: body.preferredTime ? new Date(body.preferredTime) : undefined,
+        notes: body.notes,
+        ticketId: body.ticketId,
+      },
+      idempotencyKey,
+    );
   }
 
   // ─── admin / agent ────────────────────────────────────────────────
diff --git a/packages/iios-service/src/support/support.service.ts b/packages/iios-service/src/support/support.service.ts
index a490d96..93b25de 100644
--- a/packages/iios-service/src/support/support.service.ts
+++ b/packages/iios-service/src/support/support.service.ts
@@ -6,6 +6,7 @@ import { PrismaService } from '../prisma/prisma.service';
 import { PLATFORM_PORTS } from '../platform/platform-ports';
 import { decideOrThrow } from '../platform/fail-closed';
 import { ActorResolver, type MessagePrincipal } from '../identity/actor.resolver';
+import { IdempotencyService } from '../idempotency/idempotency.service';
 
 const TICKET_TRANSITIONS: Record<IiosTicketState, IiosTicketState[]> = {
   NEW: ['OPEN', 'CANCELLED'],
@@ -29,65 +30,73 @@ export class SupportService {
     private readonly prisma: PrismaService,
     @Inject(PLATFORM_PORTS) private readonly ports: IiosPlatformPorts,
     private readonly actors: ActorResolver,
+    private readonly idempotency: IdempotencyService,
   ) {}
 
   async createTicket(
     principal: MessagePrincipal,
     input: { subject: string; priority?: IiosTicketPriority; threadId?: string; queueId?: string },
+    idempotencyKey?: string,
   ) {
     await decideOrThrow(this.ports, { action: 'iios.support.ticket.create', scope: principal });
     const scope = await this.actors.resolveScope(principal);
-    const requester = await this.actors.resolveActor(scope.id, principal);
-    const traceId = randomUUID();
 
-    // Every ticket gets a queue so assignment has somewhere to route it — find
-    // the scope's default queue or create one.
-    const queueId =
-      input.queueId ??
-      (
-        (await this.prisma.iiosSupportQueue.findFirst({ where: { scopeId: scope.id, enabled: true } })) ??
-        (await this.prisma.iiosSupportQueue.create({ data: { scopeId: scope.id, name: 'Support' } }))
-      ).id;
+    const body = async () => {
+      const requester = await this.actors.resolveActor(scope.id, principal);
+      const traceId = randomUUID();
 
-    return this.prisma.$transaction(async (tx) => {
-      const ticket = await tx.iiosTicket.create({
-        data: {
-          scopeId: scope.id,
-          queueId,
-          requesterActorId: requester.id,
-          subject: input.subject,
-          priority: input.priority ?? 'P3',
-          traceId,
-        },
+      // Every ticket gets a queue so assignment has somewhere to route it — find
+      // the scope's default queue or create one.
+      const queueId =
+        input.queueId ??
+        (
+          (await this.prisma.iiosSupportQueue.findFirst({ where: { scopeId: scope.id, enabled: true } })) ??
+          (await this.prisma.iiosSupportQueue.create({ data: { scopeId: scope.id, name: 'Support' } }))
+        ).id;
+
+      return this.prisma.$transaction(async (tx) => {
+        const ticket = await tx.iiosTicket.create({
+          data: {
+            scopeId: scope.id,
+            queueId,
+            requesterActorId: requester.id,
+            subject: input.subject,
+            priority: input.priority ?? 'P3',
+            traceId,
+          },
+        });
+        await tx.iiosTicketStateHistory.create({
+          data: { ticketId: ticket.id, toState: 'NEW', actorId: requester.id, reasonCode: 'created' },
+        });
+        if (input.threadId) {
+          await tx.iiosTicketThreadLink.create({ data: { ticketId: ticket.id, threadId: input.threadId } });
+        }
+        const event: CloudEvent = {
+          specversion: '1.0',
+          id: `evt_${ticket.id}`,
+          type: IIOS_EVENTS.ticketCreated,
+          source: `iios/support/${scope.id}`,
+          subject: `ticket/${ticket.id}`,
+          time: new Date().toISOString(),
+          datacontenttype: 'application/json',
+          insignia: { scopeSnapshotId: scope.id, correlationId: traceId, idempotencyKey: `ticket:${ticket.id}`, dataClass: 'internal' },
+          data: { ticketId: ticket.id, scopeId: scope.id, queueId, threadId: input.threadId },
+        };
+        await tx.iiosOutboxEvent.create({
+          data: {
+            aggregateType: 'ticket',
+            aggregateId: ticket.id,
+            eventType: IIOS_EVENTS.ticketCreated,
+            cloudEvent: event as unknown as Prisma.InputJsonValue,
+            partitionKey: `${scope.id}:${ticket.id}`,
+          },
+        });
+        return ticket;
       });
-      await tx.iiosTicketStateHistory.create({
-        data: { ticketId: ticket.id, toState: 'NEW', actorId: requester.id, reasonCode: 'created' },
-      });
-      if (input.threadId) {
-        await tx.iiosTicketThreadLink.create({ data: { ticketId: ticket.id, threadId: input.threadId } });
-      }
-      const event: CloudEvent = {
-        specversion: '1.0',
-        id: `evt_${ticket.id}`,
-        type: IIOS_EVENTS.ticketCreated,
-        source: `iios/support/${scope.id}`,
-        subject: `ticket/${ticket.id}`,
-        time: new Date().toISOString(),
-        datacontenttype: 'application/json',
-        insignia: { scopeSnapshotId: scope.id, correlationId: traceId, idempotencyKey: `ticket:${ticket.id}`, dataClass: 'internal' },
-        data: { ticketId: ticket.id, scopeId: scope.id, queueId, threadId: input.threadId },
-      };
-      await tx.iiosOutboxEvent.create({
-        data: {
-          aggregateType: 'ticket',
-          aggregateId: ticket.id,
-          eventType: IIOS_EVENTS.ticketCreated,
-          cloudEvent: event as unknown as Prisma.InputJsonValue,
-          partitionKey: `${scope.id}:${ticket.id}`,
-        },
-      });
-      return ticket;
-    });
+    };
+
+    if (!idempotencyKey) return body();
+    return this.idempotency.run({ scopeId: scope.id, commandName: 'support.ticket.create', key: idempotencyKey, request: input }, body);
   }
 
   /** Escalate a chat thread to support: create a ticket linked to that thread. */
@@ -156,21 +165,28 @@ export class SupportService {
   async requestCallback(
     principal: MessagePrincipal,
     input: { preferChannel: string; preferredTime?: Date; notes?: string; ticketId?: string },
+    idempotencyKey?: string,
   ) {
     await decideOrThrow(this.ports, { action: 'iios.support.callback.request', scope: principal });
     const scope = await this.actors.resolveScope(principal);
-    const requester = await this.actors.resolveActor(scope.id, principal);
-    return this.prisma.iiosCallbackRequest.create({
-      data: {
-        scopeId: scope.id,
-        requesterActorId: requester.id,
-        preferChannel: input.preferChannel,
-        preferredTime: input.preferredTime,
-        notes: input.notes,
-        ticketId: input.ticketId,
-        status: input.preferredTime ? 'SCHEDULED' : 'PENDING',
-      },
-    });
+
+    const body = async () => {
+      const requester = await this.actors.resolveActor(scope.id, principal);
+      return this.prisma.iiosCallbackRequest.create({
+        data: {
+          scopeId: scope.id,
+          requesterActorId: requester.id,
+          preferChannel: input.preferChannel,
+          preferredTime: input.preferredTime,
+          notes: input.notes,
+          ticketId: input.ticketId,
+          status: input.preferredTime ? 'SCHEDULED' : 'PENDING',
+        },
+      });
+    };
+
+    if (!idempotencyKey) return body();
+    return this.idempotency.run({ scopeId: scope.id, commandName: 'support.callback.request', key: idempotencyKey, request: input }, body);
   }
 
   async listTickets(principal: MessagePrincipal, opts: { scope: 'mine' | 'assigned' }) {
diff --git a/packages/iios-service/src/support/support.spec.ts b/packages/iios-service/src/support/support.spec.ts
index fae0b2f..288effb 100644
--- a/packages/iios-service/src/support/support.spec.ts
+++ b/packages/iios-service/src/support/support.spec.ts
@@ -5,6 +5,7 @@ import { makeFakePorts } from '@insignia/iios-testkit';
 import { PolicyDeniedError, IIOS_EVENTS } from '@insignia/iios-contracts';
 import { MessageService, type MessagePrincipal } from '../messaging/message.service';
 import { SupportService } from './support.service';
+import { IdempotencyService } from '../idempotency/idempotency.service';
 import { ActorResolver } from '../identity/actor.resolver';
 import type { PrismaService } from '../prisma/prisma.service';
 
@@ -12,7 +13,7 @@ const url = process.env.DATABASE_URL ?? 'postgresql://iios:iios@localhost:5434/i
 const prisma = new PrismaClient({ datasources: { db: { url } } });
 const asService = prisma as unknown as PrismaService;
 const actors = new ActorResolver(asService);
-const support = (ports = makeFakePorts()) => new SupportService(asService, ports, actors);
+const support = (ports = makeFakePorts()) => new SupportService(asService, ports, actors, new IdempotencyService(asService));
 const msg = () => new MessageService(asService, makeFakePorts(), actors);
 
 const cust: MessagePrincipal = { userId: 'cust', orgId: 'org_demo', appId: 'portal-demo', displayName: 'Customer' };
@@ -80,3 +81,30 @@ describe('SupportService (P4)', () => {
     expect(await prisma.iiosTicket.count()).toBe(0);
   });
 });
+
+describe('SupportService — idempotent creates (P9 slice 6)', () => {
+  it('createTicket twice with the same Idempotency-Key + body → one ticket, same id', async () => {
+    const a = await support().createTicket(cust, { subject: 'dup me' }, 'k-ticket-1');
+    const b = await support().createTicket(cust, { subject: 'dup me' }, 'k-ticket-1');
+    expect(b.id).toBe(a.id);
+    expect(await prisma.iiosTicket.count()).toBe(1); // no duplicate side-effect
+  });
+
+  it('same key + a different body → conflict', async () => {
+    await support().createTicket(cust, { subject: 'first' }, 'k-ticket-2');
+    await expect(support().createTicket(cust, { subject: 'CHANGED' }, 'k-ticket-2')).rejects.toThrow();
+    expect(await prisma.iiosTicket.count()).toBe(1);
+  });
+
+  it('no key → runs unwrapped, no ledger row', async () => {
+    await support().createTicket(cust, { subject: 'no-key' });
+    expect(await prisma.iiosIdempotencyCommand.count()).toBe(0);
+  });
+
+  it('requestCallback twice with the same key → one callback request', async () => {
+    const a = await support().requestCallback(cust, { preferChannel: 'PHONE' }, 'k-cb-1');
+    const b = await support().requestCallback(cust, { preferChannel: 'PHONE' }, 'k-cb-1');
+    expect(b.id).toBe(a.id);
+    expect(await prisma.iiosCallbackRequest.count()).toBe(1);
+  });
+});