toolsrv: export USER and NAMESPACE to shell environment

ollie-9p computes its namespace path from $USER and $DISPLAY via
client.Namespace(). When run inside the sandboxed shell, USER was not
guaranteed to be in the environment, producing /tmp/ns..:0/ollie.

Fix: explicitly inject USER into envExtra in SetSessionEnv (alongside
OLLIE_SESSION_ID and OLLIE_UNAME). Also export the computed NAMESPACE
to cmd.Env so ollie-9p can use it directly without recomputing.

agent/agent.go

@@ -266,6 +266,9 @@ func (ag *Agent) SetSessionEnv(sessionID string) {
 			if ag.id != "" {
 				es.SetEnv("OLLIE_UNAME", ag.id)
 			}
+			if u := os.Getenv("USER"); u != "" {
+				es.SetEnv("USER", u)
+			}
 		}
 	}
 }

toolsrv/shell.go

@@ -516,6 +516,10 @@ func (e *Server) executeWithStdin(ctx context.Context, code, language string, ti
 		cmd.Env = append(cmd.Env, k+"="+v)
 	}
 	e.envMu.RUnlock()
+	// Export computed NAMESPACE so tools like ollie-9p can find the server.
+	if ns := envMap["NAMESPACE"]; ns != "" {
+		cmd.Env = append(cmd.Env, "NAMESPACE="+ns)
+	}
 
 	cmd.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}
 	cmd.Cancel = func() error {