diff --git a/Fabric.Backend.Guild/src/database.config.ts b/Fabric.Backend.Guild/src/database.config.ts
index 499c9c8..966c31e 100644
--- a/Fabric.Backend.Guild/src/database.config.ts
+++ b/Fabric.Backend.Guild/src/database.config.ts
@@ -7,6 +7,7 @@ import { DmParticipant } from './entities/dm-participant.entity';
 import { GuildRole } from './entities/guild-role.entity';
 import { GuildMember } from './entities/guild-member.entity';
 import { GuildMemberRole } from './entities/guild-member-role.entity';
+import { IdempotencyRecord } from './entities/idempotency-record.entity';
 
 export const buildTypeOrmConfig = (): TypeOrmModuleOptions => ({
   type: 'mysql',
@@ -24,6 +25,7 @@ export const buildTypeOrmConfig = (): TypeOrmModuleOptions => ({
     GuildRole,
     GuildMember,
     GuildMemberRole,
+    IdempotencyRecord,
   ],
   synchronize: (process.env.DB_SYNC ?? 'true') === 'true',
   logging: (process.env.DB_LOGGING ?? 'false') === 'true',
diff --git a/Fabric.Backend.Guild/src/entities/idempotency-record.entity.ts b/Fabric.Backend.Guild/src/entities/idempotency-record.entity.ts
new file mode 100644
index 0000000..a5d6936
--- /dev/null
+++ b/Fabric.Backend.Guild/src/entities/idempotency-record.entity.ts
@@ -0,0 +1,26 @@
+import {
+  Column,
+  CreateDateColumn,
+  Entity,
+  Index,
+  PrimaryGeneratedColumn,
+} from 'typeorm';
+
+@Entity('idempotency_records')
+@Index(['scope', 'idempotencyKey'], { unique: true })
+export class IdempotencyRecord {
+  @PrimaryGeneratedColumn('uuid')
+  id!: string;
+
+  @Column({ type: 'varchar', length: 64 })
+  scope!: string;
+
+  @Column({ type: 'varchar', length: 128 })
+  idempotencyKey!: string;
+
+  @Column({ type: 'json' })
+  responseBody!: Record<string, unknown>;
+
+  @CreateDateColumn()
+  createdAt!: Date;
+}
diff --git a/Fabric.Backend.Guild/src/messaging/messaging.controller.ts b/Fabric.Backend.Guild/src/messaging/messaging.controller.ts
index 0e7cf50..07a94c3 100644
--- a/Fabric.Backend.Guild/src/messaging/messaging.controller.ts
+++ b/Fabric.Backend.Guild/src/messaging/messaging.controller.ts
@@ -3,6 +3,7 @@ import {
   Controller,
   Delete,
   Get,
+  Headers,
   NotFoundException,
   Param,
   Patch,
@@ -14,6 +15,7 @@ import { DataSource, Repository } from 'typeorm';
 import { CreateMessageDto } from './dto.create-message.dto';
 import { Channel } from '../entities/channel.entity';
 import { Message } from '../entities/message.entity';
+import { IdempotencyRecord } from '../entities/idempotency-record.entity';
 
 const EDIT_WINDOW_MS = 15 * 60 * 1000;
 const DEFAULT_PAGE_LIMIT = 50;
@@ -27,8 +29,33 @@ export class MessagingController {
     private readonly channelRepo: Repository<Channel>,
     @InjectRepository(Message)
     private readonly messageRepo: Repository<Message>,
+    @InjectRepository(IdempotencyRecord)
+    private readonly idemRepo: Repository<IdempotencyRecord>,
   ) {}
 
+  private async getIdempotentResponse(
+    scope: string,
+    idempotencyKey?: string,
+  ): Promise<Record<string, unknown> | null> {
+    if (!idempotencyKey) return null;
+    const row = await this.idemRepo.findOne({ where: { scope, idempotencyKey } });
+    return row?.responseBody ?? null;
+  }
+
+  private async saveIdempotentResponse(
+    scope: string,
+    idempotencyKey: string | undefined,
+    responseBody: Record<string, unknown>,
+  ): Promise<void> {
+    if (!idempotencyKey) return;
+    const row = this.idemRepo.create({
+      scope,
+      idempotencyKey,
+      responseBody,
+    });
+    await this.idemRepo.save(row);
+  }
+
   private toView(m: Message) {
     return {
       messageId: m.messageId,
@@ -46,7 +73,15 @@ export class MessagingController {
   }
 
   @Post()
-  async create(@Param('id') channelId: string, @Body() body: CreateMessageDto) {
+  async create(
+    @Param('id') channelId: string,
+    @Body() body: CreateMessageDto,
+    @Headers('idempotency-key') idempotencyKey?: string,
+  ) {
+    const scope = `POST:/channels/${channelId}/messages`;
+    const existed = await this.getIdempotentResponse(scope, idempotencyKey);
+    if (existed) return existed;
+
     const message = await this.dataSource.transaction(async (manager) => {
       const channel = await manager.findOne(Channel, {
         where: { id: channelId },
@@ -78,7 +113,9 @@ export class MessagingController {
       return manager.save(Message, row);
     });
 
-    return this.toView(message);
+    const responseBody = this.toView(message) as Record<string, unknown>;
+    await this.saveIdempotentResponse(scope, idempotencyKey, responseBody);
+    return responseBody;
   }
 
   @Patch(':messageId')
@@ -86,7 +123,12 @@ export class MessagingController {
     @Param('id') channelId: string,
     @Param('messageId') messageId: string,
     @Body() body: { content?: string },
+    @Headers('idempotency-key') idempotencyKey?: string,
   ) {
+    const scope = `PATCH:/channels/${channelId}/messages/${messageId}`;
+    const existed = await this.getIdempotentResponse(scope, idempotencyKey);
+    if (existed) return existed;
+
     const item = await this.messageRepo.findOne({ where: { channelId, messageId } });
     if (!item) return { status: 'not_found' };
 
@@ -99,11 +141,21 @@ export class MessagingController {
     item.content = body.content ?? item.content;
     item.editedAt = new Date();
     const saved = await this.messageRepo.save(item);
-    return this.toView(saved);
+    const responseBody = this.toView(saved) as Record<string, unknown>;
+    await this.saveIdempotentResponse(scope, idempotencyKey, responseBody);
+    return responseBody;
   }
 
   @Delete(':messageId')
-  async remove(@Param('id') channelId: string, @Param('messageId') messageId: string) {
+  async remove(
+    @Param('id') channelId: string,
+    @Param('messageId') messageId: string,
+    @Headers('idempotency-key') idempotencyKey?: string,
+  ) {
+    const scope = `DELETE:/channels/${channelId}/messages/${messageId}`;
+    const existed = await this.getIdempotentResponse(scope, idempotencyKey);
+    if (existed) return existed;
+
     const item = await this.messageRepo.findOne({ where: { channelId, messageId } });
     if (!item) return { status: 'not_found' };
 
@@ -114,7 +166,13 @@ export class MessagingController {
     item.attachments = [];
     await this.messageRepo.save(item);
 
-    return { status: 'deleted', mode: 'soft', messageId };
+    const responseBody = {
+      status: 'deleted',
+      mode: 'soft',
+      messageId,
+    } as Record<string, unknown>;
+    await this.saveIdempotentResponse(scope, idempotencyKey, responseBody);
+    return responseBody;
   }
 
   @Get()
diff --git a/Fabric.Backend.Guild/src/messaging/messaging.module.ts b/Fabric.Backend.Guild/src/messaging/messaging.module.ts
index 1ed52ac..3cba2a6 100644
--- a/Fabric.Backend.Guild/src/messaging/messaging.module.ts
+++ b/Fabric.Backend.Guild/src/messaging/messaging.module.ts
@@ -3,9 +3,10 @@ import { TypeOrmModule } from '@nestjs/typeorm';
 import { MessagingController } from './messaging.controller';
 import { Channel } from '../entities/channel.entity';
 import { Message } from '../entities/message.entity';
+import { IdempotencyRecord } from '../entities/idempotency-record.entity';
 
 @Module({
-  imports: [TypeOrmModule.forFeature([Channel, Message])],
+  imports: [TypeOrmModule.forFeature([Channel, Message, IdempotencyRecord])],
   controllers: [MessagingController],
 })
 export class MessagingModule {}
diff --git a/docs/TODO-backend-center-guild.md b/docs/TODO-backend-center-guild.md
index 4fe0b4d..97eb763 100644
--- a/docs/TODO-backend-center-guild.md
+++ b/docs/TODO-backend-center-guild.md
@@ -53,7 +53,7 @@
 ### 2.3 一致性与回补
 - [x] 回补接口：`seq_from/seq_to`
 - [x] 断片检测辅助响应字段（next_expected_seq 等）
-- [ ] 幂等键支持（写接口）
+- [x] 幂等键支持（写接口）
 
 ### 2.4 实时通信（MVP 后半）
 - [ ] WebSocket 网关接入