Initial exploration and planning

Co-authored-by: alexr00 <38270282+alexr00@users.noreply.github.com>

Author: Copilot

src/@types/vscode.proposed.chatParticipantPrivate.d.ts

@@ -55,6 +55,11 @@ declare module 'vscode' {
 		 */
 		readonly attempt: number;
 
+		/**
+		 * The session identifier for this chat request
+		 */
+		readonly sessionId: string;
+
 		/**
 		 * If automatic command detection is enabled.
 		 */