batch ChatUpdated D-Bus signals with 50ms coalescing

Previously every streaming token fired a separate D-Bus signal,
flooding the session bus and back-pressuring the HTTP stream reader.
New chatEmitter buffers text and flushes at most every 50ms. Log
writes remain immediate so GetChat always returns current data.
flushSync() drains the buffer before StateChanged signals.

main.go

@@ -11,6 +11,7 @@ import (
 	"strings"
 	"sync"
 	"syscall"
+	"time"
 
 	"github.com/godbus/dbus/v5"
 	"github.com/godbus/dbus/v5/introspect"
@@ -42,6 +43,71 @@ type managedSession struct {
 	peers  map[string]bool
 }
 
+// chatEmitter batches ChatUpdated D-Bus signals to avoid flooding the bus.
+// Text is appended to the session log immediately, but the D-Bus signal is
+// coalesced and emitted at most every 50ms.
+type chatEmitter struct {
+	conn    *dbus.Conn
+	sess    *managedSession
+	mu      sync.Mutex
+	buf     string
+	offset  int64
+	timer   *time.Timer
+	running bool
+}
+
+func newChatEmitter(conn *dbus.Conn, sess *managedSession) *chatEmitter {
+	return &chatEmitter{conn: conn, sess: sess}
+}
+
+func (e *chatEmitter) append(text string) {
+	// Write to log immediately so GetChat always returns the latest.
+	e.sess.logMu.Lock()
+	if e.buf == "" {
+		e.offset = int64(len(e.sess.log))
+	}
+	e.sess.log = append(e.sess.log, []byte(text)...)
+	e.sess.logMu.Unlock()
+
+	e.mu.Lock()
+	e.buf += text
+	if !e.running {
+		e.running = true
+		e.timer = time.AfterFunc(50*time.Millisecond, e.flush)
+	}
+	e.mu.Unlock()
+}
+
+func (e *chatEmitter) flush() {
+	e.mu.Lock()
+	text := e.buf
+	offset := e.offset
+	e.buf = ""
+	e.running = false
+	e.mu.Unlock()
+
+	if text != "" {
+		e.conn.Emit(busPath, busIface+".ChatUpdated", e.sess.id, offset, text)
+	}
+}
+
+// flushSync drains any pending buffered text immediately (used on state transitions).
+func (e *chatEmitter) flushSync() {
+	e.mu.Lock()
+	if e.timer != nil {
+		e.timer.Stop()
+	}
+	text := e.buf
+	offset := e.offset
+	e.buf = ""
+	e.running = false
+	e.mu.Unlock()
+
+	if text != "" {
+		e.conn.Emit(busPath, busIface+".ChatUpdated", e.sess.id, offset, text)
+	}
+}
+
 // SessionManager is the D-Bus exported object.
 type SessionManager struct {
 	mu       sync.RWMutex
@@ -135,6 +201,7 @@ func (m *SessionManager) CreateSession(cwd, backendName, modelName, agentName st
 	}
 
 	// Subscribe to events for the chat log + signal dispatch
+	emitter := newChatEmitter(m.conn, sess)
 	streamingRole := ""
 	core.Bus().Subscribe("event", func(ev agent.Event) {
 		var text string
@@ -175,12 +242,7 @@ func (m *SessionManager) CreateSession(cwd, backendName, modelName, agentName st
 			return
 		}
 
-		sess.logMu.Lock()
+		emitter.append(text)
-		offset := int64(len(sess.log))
-		sess.log = append(sess.log, []byte(text)...)
-		sess.logMu.Unlock()
-
-		m.conn.Emit(busPath, busIface+".ChatUpdated", sess.id, offset, text)
 	})
 
 	// Watch state changes
@@ -189,9 +251,11 @@ func (m *SessionManager) CreateSession(cwd, backendName, modelName, agentName st
 		for {
 			next, ok := core.WaitChange(ctx, agent.WatchState, current)
 			if !ok {
+				emitter.flushSync()
 				return
 			}
 			current = next
+			emitter.flushSync()
 			m.conn.Emit(busPath, busIface+".StateChanged", sess.id, current)
 
 			// Send notification when a turn completes
@@ -749,6 +813,7 @@ func (m *SessionManager) restoreSession(ps *agent.PersistedSession) error {
 	}
 
 	// Subscribe to events for the chat log + signal dispatch
+	emitter := newChatEmitter(m.conn, sess)
 	streamingRole := ""
 	core.Bus().Subscribe("event", func(ev agent.Event) {
 		var text string
@@ -789,12 +854,7 @@ func (m *SessionManager) restoreSession(ps *agent.PersistedSession) error {
 			return
 		}
 
-		sess.logMu.Lock()
+		emitter.append(text)
-		offset := int64(len(sess.log))
-		sess.log = append(sess.log, []byte(text)...)
-		sess.logMu.Unlock()
-
-		m.conn.Emit(busPath, busIface+".ChatUpdated", sess.id, offset, text)
 	})
 
 	// Watch state changes
@@ -803,9 +863,11 @@ func (m *SessionManager) restoreSession(ps *agent.PersistedSession) error {
 		for {
 			next, ok := core.WaitChange(ctx, agent.WatchState, current)
 			if !ok {
+				emitter.flushSync()
 				return
 			}
 			current = next
+			emitter.flushSync()
 			m.conn.Emit(busPath, busIface+".StateChanged", sess.id, current)
 
 			if current == "idle" {