fix(coding-agent): handle stale extension contexts

fixes #3606

packages/coding-agent/src/core/extensions/runner.ts

@@ -458,7 +458,9 @@ export class ExtensionRunner {
 		return this.shortcutDiagnostics;
 	}
 
-	invalidate(message = "This extension instance is stale after session replacement or reload."): void {
+	invalidate(
+		message = "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().",
+	): void {
 		if (!this.staleMessage) {
 			this.staleMessage = message;
 			this.runtime.invalidate(message);