feat(tui): render stage lifecycle frames as dim lines in the router feed

Stage started/completed/failed events are now injected into the router
transcript (role "stage") and rendered in Faint colour, giving the
operator a chronological in-feed view of workflow progress alongside
user/router/tool turns.

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

@@ -102,16 +102,19 @@ func (m *Model) applyServer(msg protocol.ServerMessage) {
 			s.Tools = nil
 			s.addEvent(msg.OccurredAt, "StageStarted", msg.StageID)
 		}
+		m.appendRouter(msg.SessionID, RouterEntry{"stage", "⟐ stage " + msg.StageID + " started"})
 	case protocol.TypeStageCompleted:
 		if s := m.session(msg.SessionID); s != nil {
 			s.CurrentStage = ""
 			s.addEvent(msg.OccurredAt, "StageCompleted", msg.StageID)
 		}
+		m.appendRouter(msg.SessionID, RouterEntry{"stage", "⟐ stage " + msg.StageID + " completed"})
 	case protocol.TypeStageFailed:
 		if s := m.session(msg.SessionID); s != nil {
 			s.CurrentStage = ""
 			s.addEvent(msg.OccurredAt, "StageFailed", msg.StageID)
 		}
+		m.appendRouter(msg.SessionID, RouterEntry{"stage", "⟐ stage " + msg.StageID + " failed"})
 	case protocol.TypeInferenceStarted:
 		if s := m.session(msg.SessionID); s != nil {
 			s.Active = true

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

@@ -0,0 +1,103 @@
+package app
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/correx/tui-go/internal/protocol"
+)
+
+// stageFeedModel builds a minimal model with the given router messages for the
+// selected session and calls routerRows so we can inspect the rendered lines.
+func stageFeedModel(entries []RouterEntry) Model {
+	m := NewModel(nil)
+	m.width, m.height = 120, 40
+	m.theme = NewTheme(SoftBlue)
+	sess := Session{ID: "s1", Status: "ACTIVE"}
+	m.sessions = []Session{sess}
+	m.selectedID = "s1"
+	m.sessionEntered = true
+	m.routerMessages["s1"] = entries
+	return m
+}
+
+// TestStageFrameAppearsInRouterFeed verifies that TypeStageStarted is injected
+// into the router transcript as a dim "stage" entry and renders in routerRows.
+func TestStageFrameAppearsInRouterFeed(t *testing.T) {
+	m := stageFeedModel(nil)
+
+	// Simulate server delivering a StageStarted message.
+	m.applyServer(protocol.ServerMessage{
+		Type:      protocol.TypeStageStarted,
+		SessionID: "s1",
+		StageID:   "plan",
+	})
+
+	rows := m.routerRows(80, 20)
+	joined := strings.Join(rows, "\n")
+	if !strings.Contains(joined, "plan") {
+		t.Errorf("routerRows should contain stage name 'plan', got:\n%s", joined)
+	}
+}
+
+// TestStageCompletedAppearsInRouterFeed checks StageCompleted is also injected.
+func TestStageCompletedAppearsInRouterFeed(t *testing.T) {
+	m := stageFeedModel(nil)
+
+	m.applyServer(protocol.ServerMessage{
+		Type:      protocol.TypeStageCompleted,
+		SessionID: "s1",
+		StageID:   "write_script",
+	})
+
+	rows := m.routerRows(80, 20)
+	joined := strings.Join(rows, "\n")
+	if !strings.Contains(joined, "write_script") {
+		t.Errorf("routerRows should contain stage name 'write_script', got:\n%s", joined)
+	}
+}
+
+// TestStageFailedAppearsInRouterFeed checks StageFailed is also injected.
+func TestStageFailedAppearsInRouterFeed(t *testing.T) {
+	m := stageFeedModel(nil)
+
+	m.applyServer(protocol.ServerMessage{
+		Type:      protocol.TypeStageFailed,
+		SessionID: "s1",
+		StageID:   "verify",
+	})
+
+	rows := m.routerRows(80, 20)
+	joined := strings.Join(rows, "\n")
+	if !strings.Contains(joined, "verify") {
+		t.Errorf("routerRows should contain stage name 'verify', got:\n%s", joined)
+	}
+}
+
+// TestStageFrameInterspersedWithRouterTurns verifies stage lines appear between
+// real router turns in the correct order.
+func TestStageFrameInterspersedWithRouterTurns(t *testing.T) {
+	m := stageFeedModel([]RouterEntry{
+		{"user", "start the task"},
+	})
+
+	m.applyServer(protocol.ServerMessage{
+		Type:      protocol.TypeStageStarted,
+		SessionID: "s1",
+		StageID:   "plan",
+	})
+	m.routerMessages["s1"] = append(m.routerMessages["s1"], RouterEntry{"router", "I will plan this out."})
+
+	rows := m.routerRows(80, 30)
+	joined := strings.Join(rows, "\n")
+
+	if !strings.Contains(joined, "start the task") {
+		t.Errorf("user turn missing from router rows:\n%s", joined)
+	}
+	if !strings.Contains(joined, "plan") {
+		t.Errorf("stage frame missing from router rows:\n%s", joined)
+	}
+	if !strings.Contains(joined, "I will plan") {
+		t.Errorf("router turn missing from router rows:\n%s", joined)
+	}
+}

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

@@ -354,6 +354,8 @@ func (m Model) routerRows(w, h int) []string {
 			}
 		case "tool":
 			rows = append(rows, t.span("· tool output ("+itoaLen(e.Content)+" chars) — ^x to view", t.P.Dim))
+		case "stage":
+			rows = append(rows, t.span(e.Content, t.P.Faint))
 		}
 	}
 	// keep last h rows