session: prevent duplicate sessions and agents

- CreateEmpty: atomic check-and-insert under write lock prevents TOCTOU race
- AddAgent: reject duplicate agent names, return error
- CreateAgentWithParams: propagate AddAgent error, close orphan on conflict
- persist: handle AddAgent errors during restore (log and skip)

cmd/olliesrv/internal/session/persist.go

@@ -239,7 +239,11 @@ func restoreMultiAgentSession(ps *PersistedSession) (*RestoredSession, error) {
 			})
 			ag.SetName(pa.Name)
 			ag.RequireMemoryWake()
-			sess.AddAgent(ag)
+			if err := sess.AddAgent(ag); err != nil {
+				pkgLog.Error("restore agent %s: %v", pa.ID, err)
+				ag.Close()
+				continue
+			}
 			restoredAgents = append(restoredAgents, RestoredAgent{
 				ID:       pa.ID,
 				Remote:   ps.Remote,
@@ -265,7 +269,11 @@ func restoreMultiAgentSession(ps *PersistedSession) (*RestoredSession, error) {
 			continue
 		}
 		ag.RequireMemoryWake()
-		sess.AddAgent(ag)
+		if err := sess.AddAgent(ag); err != nil {
+			pkgLog.Error("restore agent %s: %v", pa.ID, err)
+			ag.Close()
+			continue
+		}
 		restoredAgents = append(restoredAgents, RestoredAgent{
 			ID:       pa.ID,
 			Remote:   ps.Remote,

cmd/olliesrv/internal/session/registry.go

@@ -293,6 +293,7 @@ func CreateEmpty(name, remote string, yolo ...bool) (*Session, error) {
 		}
 	}
 
+	// Early check (non-atomic, avoids expensive setup in the common case).
 	mu.RLock()
 	_, exists := sessions[name]
 	mu.RUnlock()
@@ -327,7 +328,13 @@ func CreateEmpty(name, remote string, yolo ...bool) (*Session, error) {
 		sess.StartBypassLoop(pkgBypassNotify)
 	}
 
+	// Atomic check-and-insert to prevent races.
 	mu.Lock()
+	if _, exists := sessions[name]; exists {
+		mu.Unlock()
+		cancel()
+		return nil, fmt.Errorf("session already exists: %s", name)
+	}
 	sessions[name] = sess
 	mu.Unlock()
 
@@ -479,7 +486,10 @@ func CreateAgentWithParams(sessName string, p AgentParams) (*agent.Agent, error)
 		return nil, err
 	}
 
-	sess.AddAgent(ag)
+	if err := sess.AddAgent(ag); err != nil {
+		ag.Close()
+		return nil, err
+	}
 	pkgLog.Info("created agent %s in session %s (profile=%s)", ag.Name(), sessName, p.Profile)
 	return ag, nil
 }

cmd/olliesrv/internal/session/session.go

@@ -291,11 +291,18 @@ func (s *Session) FindAgent(nameOrID string) *agent.Agent {
 func (s *Session) Agents() []*agent.Agent { return s.agents }
 
 // AddAgent appends an agent to the session.
-func (s *Session) AddAgent(ag *agent.Agent) {
+// Returns false if an agent with the same name already exists.
+func (s *Session) AddAgent(ag *agent.Agent) error {
+	for _, existing := range s.agents {
+		if existing.Name() == ag.Name() {
+			return fmt.Errorf("agent already exists: %s", ag.Name())
+		}
+	}
 	s.agents = append(s.agents, ag)
 	if s.Ctx != nil {
 		go agent.ConsumeFeed(s.Ctx, ag)
 	}
+	return nil
 }
 
 // RemoveAgent removes an agent by ID and closes it.