feat(guild-messaging): add simplified message edit window policy

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

@@ -10,8 +10,11 @@ type Message = {
   mentions: string[];
   attachments: Array<{ url: string; name?: string; mimeType?: string }>;
   createdAt: string;
+  editedAt: string | null;
 };
 
+const EDIT_WINDOW_MS = 15 * 60 * 1000;
+
 @Controller('channels/:id/messages')
 export class MessagingController {
   private seqByChannel = new Map<string, number>();
@@ -31,6 +34,7 @@ export class MessagingController {
       mentions: body.mentions ?? [],
       attachments: body.attachments ?? [],
       createdAt: new Date().toISOString(),
+      editedAt: null,
     };
 
     const arr = this.messagesByChannel.get(channelId) ?? [];
@@ -45,7 +49,15 @@ export class MessagingController {
     const arr = this.messagesByChannel.get(channelId) ?? [];
     const item = arr.find((m) => m.messageId === messageId);
     if (!item) return { status: 'not_found' };
+
+    const now = Date.now();
+    const createdAt = new Date(item.createdAt).getTime();
+    if (now - createdAt > EDIT_WINDOW_MS) {
+      return { status: 'edit_window_expired', messageId };
+    }
+
     item.content = body.content ?? item.content;
+    item.editedAt = new Date().toISOString();
     return item;
   }