feat(tui): event-derived ordering + retire Kotlin TUI

Rebuild the Go TUI transcript from the event stream instead of
optimistic local echoes. ChatTurnEvent now maps to ServerMessage.ChatTurn
(chat.turn); the TUI auto-vivifies sessions and renders user+router turns
from events. SessionStarted is de-special-cased into SessionAnnounced
(still carries workflowId), dropping the router.response shadow and
optimistic echoes.

Delete the unused Kotlin TUI (apps/tui) and add a kotlinx<->Go
golden-fixture test to lock the wire protocol. Gitignore server runtime
logs.

apps/tui-go/internal/app/model.go

@@ -237,6 +237,19 @@ func (m Model) session(id string) *Session {
 	return nil
 }
 
+// ensureSession returns the session with id, creating an ACTIVE entry if absent.
+// Session existence is derived from the event stream (any event for an unknown
+// session vivifies it) rather than a dedicated control frame.
+func (m *Model) ensureSession(id string) *Session {
+	if s := m.session(id); s != nil {
+		return s
+	}
+	m.sessions = append(m.sessions, Session{
+		ID: id, Status: "ACTIVE", LastEventAt: nowMillis(),
+	})
+	return &m.sessions[len(m.sessions)-1]
+}
+
 // filteredSessions applies the workflow-id filter.
 func (m Model) filteredSessions() []Session {
 	if m.filter == "" {

apps/tui-go/internal/app/server.go

@@ -50,9 +50,24 @@ func inferCategory(t string) string {
 // applyServer mutates the model for a single (non-buffered) server message.
 func (m *Model) applyServer(msg protocol.ServerMessage) {
 	debugLog("SRV type=%s session=%s reason=%s", msg.Type, msg.SessionID, msg.Reason)
+	// Auto-vivify: any event for an unknown session creates it, so session
+	// existence is derived from the event stream, not a dedicated control frame.
+	if msg.IsEventBearing() && msg.SessionID != "" {
+		m.ensureSession(msg.SessionID)
+	}
 	switch msg.Type {
-	case protocol.TypeSessionStarted:
-		m.onSessionStarted(msg)
+	case protocol.TypeSessionAnnounced:
+		m.onSessionAnnounced(msg)
+	case protocol.TypeChatTurn:
+		m.routerConnected = true
+		role := "router"
+		if msg.Role == "USER" {
+			role = "user"
+		}
+		m.appendRouter(msg.SessionID, RouterEntry{role, msg.Content})
+		if s := m.session(msg.SessionID); s != nil {
+			s.LastEventAt = nowMillis()
+		}
 	case protocol.TypeSessionPaused:
 		label := "PAUSED"
 		if msg.Reason == "APPROVAL_PENDING" {
@@ -183,9 +198,6 @@ func (m *Model) applyServer(msg protocol.ServerMessage) {
 		} else {
 			m.providerType = "REMOTE"
 		}
-	case protocol.TypeRouterResponse:
-		m.routerConnected = true
-		m.appendRouter(msg.SessionID, RouterEntry{"router", msg.Content})
 	case protocol.TypeWorkflowList:
 		m.workflows = m.workflows[:0]
 		for _, w := range msg.Workflows {
@@ -227,30 +239,23 @@ func sessionIDOf(msg protocol.ServerMessage) string {
 	}
 }
 
-func (m *Model) onSessionStarted(msg protocol.ServerMessage) {
-	hadOptimistic := false
-	cleaned := m.sessions[:0:0]
-	for _, s := range m.sessions {
-		if s.Status == "STARTING" {
-			hadOptimistic = true
-			continue
-		}
-		cleaned = append(cleaned, s)
-	}
-	cleaned = append(cleaned, Session{
-		ID: msg.SessionID, Status: "ACTIVE", WorkflowID: msg.WorkflowID,
-		Name: msg.WorkflowID, LastEventAt: nowMillis(),
-	})
-	m.sessions = cleaned
-	if hadOptimistic || m.selectedID == "" {
-		m.selectedID = msg.SessionID
+// onSessionAnnounced fills in a session's workflow identity (the announce is the
+// only event carrying workflowId) and applies auto-focus. The session entry itself
+// was already created by the auto-vivify path in applyServer.
+func (m *Model) onSessionAnnounced(msg protocol.ServerMessage) {
+	s := m.ensureSession(msg.SessionID)
+	s.Status = "ACTIVE"
+	if msg.WorkflowID != "" {
+		s.WorkflowID = msg.WorkflowID
+		s.Name = msg.WorkflowID
 	}
+	s.LastEventAt = nowMillis()
 	if m.pendingWorkflowFocus {
 		m.selectedID = msg.SessionID
 		m.sessionEntered = true
 		m.pendingWorkflowFocus = false
-	} else {
-		m.sessionEntered = true
+	} else if m.selectedID == "" {
+		m.selectedID = msg.SessionID
 	}
 }
 

apps/tui-go/internal/app/update.go

@@ -545,15 +545,14 @@ func (m Model) submit() (tea.Model, tea.Cmd) {
 		if text == "" {
 			return m, nil
 		}
-		// New optimistic chat session.
+		// New chat session. The client owns the id, so create the entry locally and
+		// focus it; the USER/ROUTER turns arrive as chat.turn events (no optimistic echo).
 		id := newSessionID()
-		m.sessions = append(m.sessions, Session{
-			ID: id, Status: "STARTING", WorkflowID: "chat", Name: "chat",
-			LastEventAt: nowMillis(),
-		})
+		s := m.ensureSession(id)
+		s.WorkflowID = "chat"
+		s.Name = "chat"
 		m.selectedID = id
 		m.sessionEntered = true
-		m.appendRouter(id, RouterEntry{"user", text})
 		m.client.Send(protocol.StartChatSession(id, text))
 		m.clearInput()
 		return m, nil
@@ -569,7 +568,7 @@ func (m Model) submit() (tea.Model, tea.Cmd) {
 			hist = hist[len(hist)-50:]
 		}
 		m.history[sid] = hist
-		m.appendRouter(sid, RouterEntry{"user", text})
+		// No optimistic echo — the USER turn arrives as a chat.turn event.
 		m.client.Send(protocol.ChatInput(sid, text, m.chatMode))
 		m.clearInput()
 		return m, nil