feat(guild-messaging): implement soft delete strategy for messages

Fabric.Backend.Guild/src/messaging/messaging.controller.ts

@@ -11,6 +11,8 @@ type Message = {
   attachments: Array<{ url: string; name?: string; mimeType?: string }>;
   createdAt: string;
   editedAt: string | null;
+  deletedAt: string | null;
+  isDeleted: boolean;
 };
 
 const EDIT_WINDOW_MS = 15 * 60 * 1000;
@@ -35,6 +37,8 @@ export class MessagingController {
       attachments: body.attachments ?? [],
       createdAt: new Date().toISOString(),
       editedAt: null,
+      deletedAt: null,
+      isDeleted: false,
     };
 
     const arr = this.messagesByChannel.get(channelId) ?? [];
@@ -64,9 +68,16 @@ export class MessagingController {
   @Delete(':messageId')
   remove(@Param('id') channelId: string, @Param('messageId') messageId: string) {
     const arr = this.messagesByChannel.get(channelId) ?? [];
-    const next = arr.filter((m) => m.messageId !== messageId);
-    this.messagesByChannel.set(channelId, next);
-    return { status: 'deleted', messageId };
+    const item = arr.find((m) => m.messageId === messageId);
+    if (!item) return { status: 'not_found' };
+
+    item.isDeleted = true;
+    item.deletedAt = new Date().toISOString();
+    item.content = '[deleted]';
+    item.mentions = [];
+    item.attachments = [];
+
+    return { status: 'deleted', mode: 'soft', messageId };
   }
 
   @Get()

docs/TODO-backend-center-guild.md

@@ -46,7 +46,7 @@
 ### 2.2 消息主链路
 - [x] 发送消息（content/reply/mentions/attachments 元数据）
 - [x] 编辑消息（可编辑窗口策略先简化）
-- [ ] 删除消息（软删 vs 硬删，先定策略）
+- [x] 删除消息（软删 vs 硬删，先定策略）
 - [ ] `GET messages` 分页（seq 区间 + limit）
 - [ ] seq 分配改为 DB 原子方案（避免并发冲突）