9p: call Close() on all sessions during shutdown

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/p9/server.go

@@ -1377,6 +1377,19 @@ func (s *Server) createSession(args []string) error {
 	return nil
 }
 
+// Shutdown kills all active sessions, triggering Close() on each core.
+func (s *Server) Shutdown() {
+	s.mu.Lock()
+	ids := make([]string, 0, len(s.sessions))
+	for id := range s.sessions {
+		ids = append(ids, id)
+	}
+	s.mu.Unlock()
+	for _, id := range ids {
+		s.killSession(id)
+	}
+}
+
 func (s *Server) killSession(id string) {
 	s.mu.Lock()
 	sess := s.sessions[id]

main.go

@@ -160,6 +160,7 @@ func runServer(sockPath, pidPath string) {
 	<-sigChan
 
 	fmt.Println("shutting down")
+	srv.Shutdown()
 	if fuseCmd != nil {
 		exec.Command("fusermount", "-u", mnt).Run() //nolint:errcheck
 		fuseCmd.Wait()                               //nolint:errcheck