session: support multiple agents in data structures

- session.Session: r *agent.Agent → agents []*agent.Agent
  - Agent() returns agents[0] for backward compat
  - Added Agents(), AgentAt(), AgentCount(), AddAgent()
  - Close/SetEnv/SetSessionID iterate all agents
  - Other methods use Agent() (primary agent)
- fs/session: AgentLog *AgentLog → AgentLogs map[string]*AgentLog
  - Added AgentLog() (returns first) and SetAgentLog(id, al) methods
  - Updated create.go, persist.go, root.go, olliesrv/server.go

cmd/olliesrv/server.go

@@ -1373,8 +1373,8 @@ func (s *Server) makeStat(path string) plan9.Dir {
 		if len(parts) == 5 && parts[0] == "session" && parts[2] == "agent" {
 			if sess := fs.Lookup(s.sessionTree, parts[1]); sess != nil {
 				if base == "log" || base == "chat" {
-					if sess.AgentLog != nil {
-						length, vers := sess.AgentLog.LogInfo()
+					if al := sess.AgentLog(); al != nil {
+						length, vers := al.LogInfo()
 						if length > 64*1024 {
 							length = 64 * 1024
 						}

fs/session/create.go

@@ -269,7 +269,7 @@ func CreateAgent(rs *rootState, sessName string, args []string) error {
 	sess.mu.Lock()
 	sess.Core = core
 	sess.uname = uname
-	sess.AgentLog = al
+	sess.SetAgentLog(uname, al)
 	sess.proc = proc
 	sess.mu.Unlock()
 

fs/session/persist.go

@@ -332,26 +332,27 @@ func restoreSession(rs *rootState, ps *agent.PersistedAgent) error {
 		BaseLayers:     []string{sysPrompt, opModel, envBlock},
 		Log:            rs.cfg.Sink.NewLogger("core"),
 		Output:         NewEventHandler(al),
-		ReadPlanStep: func() string {
-			if sessPtr == nil || sessPtr.AgentLog == nil {
-				return ""
-			}
-			sessPtr.AgentLog.mu.RLock()
-			data := make([]byte, len(sessPtr.AgentLog.plan))
-			copy(data, sessPtr.AgentLog.plan)
-			sessPtr.AgentLog.mu.RUnlock()
-			return coresession.NextUncheckedStep(data)
-		},
-	})
+ReadPlanStep: func() string {
+				if sessPtr == nil || sessPtr.AgentLog() == nil {
+					return ""
+				}
+				al := sessPtr.AgentLog()
+				al.mu.RLock()
+				data := make([]byte, len(al.plan))
+				copy(data, al.plan)
+				al.mu.RUnlock()
+				return coresession.NextUncheckedStep(data)
+			},
+		})
 
-	sessionCtx, sessionCancel := context.WithCancel(rs.cfg.Ctx)
-	sess := NewSession(sessID, core, sessionCtx, sessionCancel)
-	sessPtr = sess
-	sess.uname = uname
-	sess.AgentLog = al
-	sess.proc = proc
+		sessionCtx, sessionCancel := context.WithCancel(rs.cfg.Ctx)
+		sess := NewSession(sessID, core, sessionCtx, sessionCancel)
+		sessPtr = sess
+		sess.uname = uname
+		sess.SetAgentLog(uname, al)
+		sess.proc = proc
 
-	replayMessagesToLog(sess.AgentLog, ps.Messages)
+		replayMessagesToLog(sess.AgentLog(), ps.Messages)
 
 	name := sess.Name()
 	rs.mu.Lock()

fs/session/root.go

@@ -231,7 +231,7 @@ func openSessionTree(rs *rootState, sess *Session) *Tree {
 func openAgentTree(rs *rootState, sess *Session) *Tree {
 	return NewAgentTree(
 		sess,
-		sess.AgentLog,
+		sess.AgentLog(),
 		rs.cfg.Log,
 		nil,
 		rs.cfg.InvalidateModels,

fs/session/types.go

@@ -23,8 +23,9 @@ type Session struct {
 	cancel     context.CancelFunc
 	proc       *toolsrv.Process // toolsrv subprocess (session owns lifecycle)
 
-	// AgentLog for the session's agent (will become a map when multi-agent lands).
-	AgentLog *AgentLog
+	// AgentLogs for the session's agents, keyed by agent ID.
+	// Backward compat: AgentLog() returns the first agent's log (by map iteration order).
+	AgentLogs map[string]*AgentLog
 
 	// Cached model list (expensive API call; refreshed every 24h).
 	modelsMu      sync.Mutex
@@ -62,6 +63,28 @@ func NewSession(id string, core *session.Session, ctx context.Context, cancel co
 	return sess
 }
 
+// AgentLog returns the first agent's log for backward compatibility.
+// The iteration order over the map is non-deterministic; when multi-agent
+// support is fully wired, callers should use AgentLogs directly by key.
+func (sess *Session) AgentLog() *AgentLog {
+	sess.mu.RLock()
+	defer sess.mu.RUnlock()
+	for _, al := range sess.AgentLogs {
+		return al
+	}
+	return nil
+}
+
+// SetAgentLog stores the agent log for the given agent ID.
+func (sess *Session) SetAgentLog(agentID string, al *AgentLog) {
+	sess.mu.Lock()
+	defer sess.mu.Unlock()
+	if sess.AgentLogs == nil {
+		sess.AgentLogs = make(map[string]*AgentLog)
+	}
+	sess.AgentLogs[agentID] = al
+}
+
 const modelsCacheTTL = 24 * time.Hour
 
 // CachedListModels returns the model list, using a 24h cache to avoid

session/session.go

@@ -43,7 +43,7 @@ type Config struct {
 }
 
 // Session is the concrete session type. It owns session-level state and
-// delegates agent operations to its owned Agent.
+// delegates agent operations to its owned agents.
 type Session struct {
 	id         string
 	envMu      sync.RWMutex
@@ -51,7 +51,7 @@ type Session struct {
 	plan       []byte
 	prevPrompt string
 
-	r            *agent.Agent
+	agents       []*agent.Agent
 	log          *olog.Logger
 	sessionsDir  string
 	listHandlers map[string]func() []string
@@ -133,6 +133,7 @@ func New(cfg Config) *Session {
 	a := &Session{
 		id:           cfg.SessionID,
 		env:          make(map[string]string),
+		agents:       make([]*agent.Agent, 0, 1),
 		log:          log,
 		auditLog:     auditLog,
 		sessionsDir:  cfg.SessionsDir,
@@ -140,7 +141,7 @@ func New(cfg Config) *Session {
 		listHandlers: cfg.ListHandlers,
 	}
 
-	a.r = agent.NewAgent(agent.AgentCfg{
+	ag := agent.NewAgent(agent.AgentCfg{
 		History:        cfg.History,
 		Runtime:        rt,
 		AgentName:      cfg.AgentName,
@@ -159,42 +160,76 @@ func New(cfg Config) *Session {
 		ReadPlanStep:   cfg.ReadPlanStep,
 		SaveSession:    a.saveSession,
 		FlushSave:      a.flushSave,
-	})
+})
 
-	a.r.SetSessionEnv(a.id)
+	a.agents = append(a.agents, ag)
+	ag.SetSessionEnv(a.id)
 	return a
 }
 
+// Agent returns the first (primary) agent. Backward compatible.
+func (a *Session) Agent() *agent.Agent {
+	if len(a.agents) == 0 {
+		return nil
+	}
+	return a.agents[0]
+}
+
+// Agents returns the full agent slice.
+func (a *Session) Agents() []*agent.Agent { return a.agents }
+
+// AgentAt returns the agent at the given index, or nil.
+func (a *Session) AgentAt(idx int) *agent.Agent {
+	if idx < 0 || idx >= len(a.agents) {
+		return nil
+	}
+	return a.agents[idx]
+}
+
+// AgentCount returns the number of agents.
+func (a *Session) AgentCount() int { return len(a.agents) }
+
+// AddAgent appends an agent to the session.
+func (a *Session) AddAgent(ag *agent.Agent) {
+	a.agents = append(a.agents, ag)
+	ag.SetSessionEnv(a.id)
+}
+
 // Close releases resources for this session.
 func (a *Session) Close() {
 	a.log.Debug("Close() session=%q", a.id)
 	a.flushSave()
-	a.r.Close()
+	for _, ag := range a.agents {
+		ag.Close()
+	}
 	if a.id != "" {
 		os.RemoveAll(filepath.Join(ollieTmpDir(), a.id)) //nolint:errcheck
 	}
 }
 
-// SetEnv stores a session-scoped variable and propagates it to the agent.
+// SetEnv stores a session-scoped variable and propagates to all agents.
 func (a *Session) SetEnv(key, value string) {
 	a.envMu.Lock()
 	a.env[key] = value
 	a.envMu.Unlock()
-	a.r.SetEnv(key, value)
+	for _, ag := range a.agents {
+		ag.SetEnv(key, value)
+	}
 }
 
-func (a *Session) Agent() *agent.Agent    { return a.r }
-
-// CWD returns the current working directory for tool execution.
+// CWD returns the current working directory for tool execution
+// (from the primary agent).
 func (a *Session) CWD() string {
-	if c := a.r.Cwd(); c != "" {
-		return c
+	if ag := a.Agent(); ag != nil {
+		if c := ag.Cwd(); c != "" {
+			return c
+		}
 	}
 	wd, _ := os.Getwd()
 	return wd
 }
 
-// SetCWD validates and sets the working directory.
+// SetCWD validates and sets the working directory on the primary agent.
 func (a *Session) SetCWD(dir string) error {
 	dir = paths.ExpandHome(dir)
 	if dir != "" {
@@ -202,7 +237,9 @@ func (a *Session) SetCWD(dir string) error {
 			return fmt.Errorf("cwd: %w", err)
 		}
 	}
-	a.r.SetCWD(dir)
+	if ag := a.Agent(); ag != nil {
+		ag.SetCWD(dir)
+	}
 	return nil
 }
 
@@ -223,42 +260,50 @@ func (a *Session) SetSessionID(newID string) error {
 		}
 	}
 	a.id = newID
-	a.r.RenamePreamble(oldID, newID)
+	for _, ag := range a.agents {
+		ag.RenamePreamble(oldID, newID)
+	}
 	oldTemp := filepath.Join(ollieTmpDir(), oldID)
 	newTemp := filepath.Join(ollieTmpDir(), newID)
 	if _, err := os.Stat(oldTemp); err == nil {
 		os.Rename(oldTemp, newTemp) //nolint:errcheck
 	}
-	a.r.SetSessionEnv(newID)
+	if ag := a.Agent(); ag != nil {
+		ag.SetSessionEnv(newID)
+	}
 	return nil
 }
 
 // WaitChange blocks until the named field changes from current.
 func (a *Session) WaitChange(ctx context.Context, field, current string) (string, bool) {
+	ag := a.Agent()
+	if ag == nil {
+		return "", false
+	}
 	if field == agent.WatchState {
-		return a.r.WaitChange(ctx, field, current)
+		return ag.WaitChange(ctx, field, current)
 	}
 	// Other fields — read via agent methods, use agent's change signal.
 	read := func() string {
 		switch field {
 		case "usage":
-			return a.r.UsageStr()
+			return ag.UsageStr()
 		case "ctxsz":
-			return a.r.CtxSz()
+			return ag.CtxSz()
 		case "cwd":
 			return a.CWD()
 		case "agent":
-			return a.r.Name()
+			return ag.Name()
 		}
 		return ""
 	}
-	stop := context.AfterFunc(ctx, func() { a.r.BroadcastChange() })
+	stop := context.AfterFunc(ctx, func() { ag.BroadcastChange() })
 	defer stop()
 	for ctx.Err() == nil {
 		if v := read(); v != current {
 			return v, true
 		}
-		a.r.WaitForChange(ctx)
+		ag.WaitForChange(ctx)
 	}
 	return "", false
 }
@@ -293,12 +338,17 @@ func (a *Session) flushSave() {
 		a.log.Error("session save: %v", err)
 		return
 	}
-	if err := a.r.SaveFull(path, a.id, a.CWD(), a.remote); err != nil {
-		a.log.Error("session save: %v", err)
+	if ag := a.Agent(); ag != nil {
+		if err := ag.SaveFull(path, a.id, a.CWD(), a.remote); err != nil {
+			a.log.Error("session save: %v", err)
+		}
 	}
 }
 
 // SaveSession writes the current session state to the given path.
 func (a *Session) SaveSession(path string) error {
-	return a.r.SaveFull(path, a.id, a.CWD(), a.remote)
+	if ag := a.Agent(); ag != nil {
+		return ag.SaveFull(path, a.id, a.CWD(), a.remote)
+	}
+	return fmt.Errorf("no agent in session")
 }