Fix followups going to participant ID (microsoft#209114)

Fix microsoft/vscode-copilot#4861

Author: roblourens

src/vs/workbench/contrib/chat/browser/chatWidget.ts

@@ -538,7 +538,13 @@ export class ChatWidget extends Disposable implements IChatWidget {
 
 			let msg = '';
 			if (e.followup.agentId && e.followup.agentId !== this.chatAgentService.getDefaultAgent(this.location)?.id) {
-				msg = `${chatAgentLeader}${e.followup.agentId} `;
+				const agent = this.chatAgentService.getAgent(e.followup.agentId);
+				if (!agent) {
+					return;
+				}
+
+				this.lastSelectedAgent = agent;
+				msg = `${chatAgentLeader}${agent.name} `;
 				if (e.followup.subCommand) {
 					msg += `${chatSubcommandLeader}${e.followup.subCommand} `;
 				}