fix: wire up event handler so chat stream receives events

After the fs/session refactor, NewEventHandler was defined but never
called. Agents created via session restore or CreateAgent had nil
output handlers, so emit() was a no-op and the chat stream stayed empty.

- Add Agent.SetOutput() to allow setting the event handler post-creation
- Wire up SetOutput(NewEventHandler(al)) in fs/newroot.go for restored sessions
- Wire up SetOutput(NewEventHandler(al)) in fs/handlers.go for new agents
- Also includes expanded UsageStats fields and TaskState persistence

agent/agent.go

@@ -79,12 +79,24 @@ func (ag *Agent) Messages() []backend.Message {
 	return ag.history.history()
 }
 
+// TaskState returns the current task state, if any.
+func (ag *Agent) TaskState() *TaskState {
+	if ag.history == nil {
+		return nil
+	}
+	return ag.history.TaskState
+}
+
 // UsageStats holds token usage and cost information.
 type UsageStats struct {
-	TotalInputTokens  int
-	TotalOutputTokens int
-	TotalRequests     int
-	SessionCostUSD    float64
+	TotalInputTokens         int
+	TotalCachedInputTokens   int
+	TotalCacheCreationTokens int
+	TotalOutputTokens        int
+	TotalRequests            int
+	Estimated                bool
+	LastTurnCostUSD          float64
+	SessionCostUSD           float64
 }
 
 // Usage returns the agent's usage statistics.
@@ -93,10 +105,14 @@ func (ag *Agent) Usage() *UsageStats {
 		return nil
 	}
 	return &UsageStats{
-		TotalInputTokens:  ag.history.TotalInputTokens,
-		TotalOutputTokens: ag.history.TotalOutputTokens,
-		TotalRequests:     ag.history.TotalRequests,
-		SessionCostUSD:    ag.history.SessionCostUSD,
+		TotalInputTokens:         ag.history.TotalInputTokens,
+		TotalCachedInputTokens:   ag.history.TotalCachedInputTokens,
+		TotalCacheCreationTokens: ag.history.TotalCacheCreationTokens,
+		TotalOutputTokens:        ag.history.TotalOutputTokens,
+		TotalRequests:            ag.history.TotalRequests,
+		Estimated:                ag.history.Estimated,
+		LastTurnCostUSD:          ag.history.LastTurnCostUSD,
+		SessionCostUSD:           ag.history.SessionCostUSD,
 	}
 }
 
@@ -221,6 +237,12 @@ func (ag *Agent) emit(ev Event) {
 	}
 }
 
+// SetOutput sets the agent's event output handler.
+// This allows the fs layer to wire up the event handler after agent creation.
+func (ag *Agent) SetOutput(h EventHandler) {
+	ag.output = h
+}
+
 // CWD returns the agent's working directory.
 func (ag *Agent) Cwd() string {
 	ag.stateMu.RLock()

fs/handlers.go

@@ -393,9 +393,10 @@ func requestAgentNew(ctx HandlerCtx, data []byte) ([]byte, error) {
 	if err != nil {
 		return nil, fmt.Errorf("create agent: %w", err)
 	}
-	// Create AgentLog for this agent
+	// Create AgentLog for this agent and wire up the event handler
 	al := NewAgentLog("")
 	ctx.Session.SetAgentLog(ag.ID(), al)
+	ag.SetOutput(NewEventHandler(al))
 	return []byte(ag.ID() + "\n"), nil
 }
 

fs/newroot.go

@@ -83,6 +83,10 @@ func NewRoot(cfg Config) *Tree {
 			al := NewAgentLog(ra.Remote)
 			node.SetAgentLog(ra.ID, al)
 			replayMessagesToLog(al, ra.Messages)
+			// Wire up the event handler so agent events flow to the AgentLog
+			if ag := r.Session.FindAgent(ra.ID); ag != nil {
+				ag.SetOutput(NewEventHandler(al))
+			}
 		}
 	}
 

session/persist.go

@@ -31,11 +31,16 @@ type PersistedAgent struct {
 	Backend  string            `json:"backend"`
 	Model    string            `json:"model"`
 	Messages []backend.Message `json:"messages"`
+	TaskState *agent.TaskState `json:"taskState,omitempty"`
 	// Usage tracking
-	TotalInputTokens  int     `json:"totalInputTokens,omitempty"`
-	TotalOutputTokens int     `json:"totalOutputTokens,omitempty"`
-	TotalRequests     int     `json:"totalRequests,omitempty"`
-	SessionCostUSD    float64 `json:"sessionCostUSD,omitempty"`
+	TotalInputTokens         int     `json:"totalInputTokens,omitempty"`
+	TotalCachedInputTokens   int     `json:"totalCachedInputTokens,omitempty"`
+	TotalCacheCreationTokens int     `json:"totalCacheCreationTokens,omitempty"`
+	TotalOutputTokens        int     `json:"totalOutputTokens,omitempty"`
+	TotalRequests            int     `json:"totalRequests,omitempty"`
+	Estimated                bool    `json:"estimated,omitempty"`
+	LastTurnCostUSD          float64 `json:"lastTurnCostUSD,omitempty"`
+	SessionCostUSD           float64 `json:"sessionCostUSD,omitempty"`
 }
 
 // ActiveSessionsDir returns the directory for persisted sessions.
@@ -63,17 +68,22 @@ func PersistSession(name string) error {
 
 	for _, ag := range agents {
 		pa := PersistedAgent{
-			ID:       ag.ID(),
-			Name:     ag.Name(),
-			Profile:  ag.Profile(),
-			Backend:  ag.BackendName(),
-			Model:    ag.ModelName(),
-			Messages: ag.Messages(),
+			ID:        ag.ID(),
+			Name:      ag.Name(),
+			Profile:   ag.Profile(),
+			Backend:   ag.BackendName(),
+			Model:     ag.ModelName(),
+			Messages:  ag.Messages(),
+			TaskState: ag.TaskState(),
 		}
 		if usage := ag.Usage(); usage != nil {
 			pa.TotalInputTokens = usage.TotalInputTokens
+			pa.TotalCachedInputTokens = usage.TotalCachedInputTokens
+			pa.TotalCacheCreationTokens = usage.TotalCacheCreationTokens
 			pa.TotalOutputTokens = usage.TotalOutputTokens
 			pa.TotalRequests = usage.TotalRequests
+			pa.Estimated = usage.Estimated
+			pa.LastTurnCostUSD = usage.LastTurnCostUSD
 			pa.SessionCostUSD = usage.SessionCostUSD
 		}
 		ps.Agents = append(ps.Agents, pa)