fix(coding-agent): handle stale extension contexts

fixes #3606

packages/coding-agent/src/core/agent-session.ts

@@ -724,7 +724,7 @@ export class AgentSession {
 	 */
 	dispose(): void {
 		this._extensionRunner.invalidate(
-			"This extension instance is stale after session replacement or reload. Use the provided replacement-session context instead.",
+			"This extension ctx is stale after session replacement or reload. Do not use a captured pi or command ctx after ctx.newSession(), ctx.fork(), ctx.switchSession(), or ctx.reload(). For newSession, fork, and switchSession, move post-replacement work into withSession and use the ctx passed to withSession. For reload, do not use the old ctx after await ctx.reload().",
 		);
 		this._disconnectFromAgent();
 		this._eventListeners = [];