diff --git a/frontend/src/types/ws-messages.ts b/frontend/src/types/ws-messages.ts
index a16d8fe1..aa22e1c6 100644
--- a/frontend/src/types/ws-messages.ts
+++ b/frontend/src/types/ws-messages.ts
@@ -170,6 +170,7 @@ interface UserMessageMsg {
   v: 2;
   messageId: string;
   text: string;
+  sessionId?: string;
 }
 
 interface SessionRenamedMsg {
diff --git a/server/chat.ts b/server/chat.ts
index 819914f9..dcb8c7fd 100644
--- a/server/chat.ts
+++ b/server/chat.ts
@@ -929,7 +929,7 @@ async function _startChatInner(
       });
       eventStore.updateLastSpeaker(options.resume, 'user');
       _onSessionChange?.(clientId, 'user_message');
-      const echo = { type: 'user_message', messageId, text: fullPrompt };
+      const echo = { type: 'user_message', v: 2, messageId, text: fullPrompt, sessionId: options.resume };
       send(transport, echo);
       broadcastToObservers(session.observers, echo);
     }
@@ -1055,7 +1055,7 @@ export function sendToChat(
         /* errors logged internally */
       });
     }
-    const echo = { type: 'user_message', messageId, text: fullPrompt };
+    const echo = { type: 'user_message', v: 2, messageId, text: fullPrompt, ...(session.sessionId ? { sessionId: session.sessionId } : {}) };
     send(session.transport, echo);
     broadcastToObservers(session.observers, echo);
     session.inputQueue.push(makeUserMessage(fullPrompt, 'next'));
@@ -1089,7 +1089,7 @@ export async function interruptChat(
       eventStore.updateLastSpeaker(session.sessionId, 'user');
       _onSessionChange?.(clientId, 'user_message');
     }
-    const echo = { type: 'user_message', messageId, text: fullPrompt };
+    const echo = { type: 'user_message', v: 2, messageId, text: fullPrompt, ...(session.sessionId ? { sessionId: session.sessionId } : {}) };
     send(session.transport, echo);
     broadcastToObservers(session.observers, echo);
     // Stop all active subagent tasks before interrupting the parent query.