restore/undo for deleted messages — backend + UI

- POST /api/channels/{id}/messages/{msg_id}/restore — undeletes a message
- Any user can restore (not just the deleter)
- Broadcasts restored message via WebSocket
- UI: "undo" button in floating pill on deleted messages
- API: restoreMessage() in api.ts

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/colony/src/App.tsx

@@ -1,7 +1,7 @@
 import { useCallback, useEffect, useRef, useState } from "react";
 import type { Channel } from "@/types/Channel";
 import type { Message } from "@/types/Message";
-import { getChannels, getMessages, getCurrentUsername, deleteMessage } from "@/api";
+import { getChannels, getMessages, getCurrentUsername, deleteMessage, restoreMessage } from "@/api";
 import { ChannelSidebar } from "@/components/ChannelSidebar";
 import { MessageItem } from "@/components/MessageItem";
 import { ComposeBox } from "@/components/ComposeBox";
@@ -251,6 +251,14 @@ export default function App() {
                         // ignore
                       }
                     }}
+                    onRestore={async (chId, msgId) => {
+                      try {
+                        await restoreMessage(chId, msgId);
+                        loadMessages();
+                      } catch {
+                        // ignore
+                      }
+                    }}
                   />
                 </div>
               );

ui/colony/src/api.ts

@@ -85,3 +85,14 @@ export async function deleteMessage(
   );
   if (!res.ok) throw new Error(`${res.status}: ${await res.text()}`);
 }
+
+export async function restoreMessage(
+  channelId: string,
+  msgId: string,
+): Promise<Message> {
+  return json(
+    await fetch(`${BASE}/channels/${channelId}/messages/${msgId}/restore`, {
+      method: "POST",
+    }),
+  );
+}

ui/colony/src/components/MessageItem.tsx

@@ -11,6 +11,7 @@ interface Props {
   replyTarget?: Message;
   onSelect: (id: string) => void;
   onDelete: (channelId: string, msgId: string) => void;
+  onRestore: (channelId: string, msgId: string) => void;
   currentUsername: string;
   selected: boolean;
 }
@@ -72,7 +73,7 @@ function userHue(username: string): number {
   return Math.abs(hash) % 360;
 }
 
-export function MessageItem({ message, compact, replyTarget, onSelect, onDelete, currentUsername, selected }: Props) {
+export function MessageItem({ message, compact, replyTarget, onSelect, onDelete, onRestore, currentUsername, selected }: Props) {
   const [metaOpen, setMetaOpen] = useState(false);
   const isAgent = message.user.role === "agent";
   const isDeleted = !!message.deleted_at;
@@ -193,6 +194,16 @@ export function MessageItem({ message, compact, replyTarget, onSelect, onDelete,
               ×
             </button>
           )}
+          {isDeleted && (
+            <button
+              type="button"
+              onClick={(e) => { e.stopPropagation(); onRestore(message.channel_id, message.id); }}
+              className="px-2.5 py-1.5 text-[10px] font-mono text-muted-foreground hover:text-primary hover:bg-muted/50 transition-colors border-l-2 border-border"
+              title="Restore deleted message"
+            >
+              undo
+            </button>
+          )}
         </div>
 
         {/* Content */}