feat(tui): truthful-state §2 — last-event clock + unknown-event raw fallback

Implements the load-bearing TUI-requirements §2 hard requirements:

- Last-event clock: "last event Ns ago" always visible in the status bar while
  in-session, updating every frame tick. Turns warn-colored when an active session
  has gone quiet past the stale threshold — the "thinking vs hung" tell. The
  WebSocket connection indicator (●/◌/○) already covers immediate drop visibility.
- Unknown-event raw fallback: applyServer now surfaces any unrecognized,
  session-scoped event type as a raw row in the event stream instead of silently
  dropping it (the frontend must not lie by omission). Recognized-but-unrendered
  types (router.response, protocol_error) get an explicit no-op so the default
  branch means genuinely unknown.

Tests: agoLabel formatting, unknown-event surfaces-as-row, known-ignored
no-spurious-row. Preview "session" frame exercises the clock.

Deferred: the full Go↔Kotlin per-event-type render matrix (§2 last bullet) — a
larger fixture effort than the core behaviors landed here.

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

@@ -48,6 +48,7 @@ func PreviewFrame(kind string, w, h int) string {
 			s.Events = sampleEvents()
 			s.Active = true
 			s.ToolsByStage = sampleManifest()
+			s.LastEventAt = nowMillis() - 3000 // 3s ago — exercises the last-event clock
 		}
 		if kind == "insert" {
 			m.editMode = ModeInsert

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

@@ -322,6 +322,22 @@ func (m *Model) applyServer(msg protocol.ServerMessage) {
 		if m.configIndex >= len(m.configFields) {
 			m.configIndex = 0
 		}
+	case protocol.TypeRouterResponse, protocol.TypeProtocolError:
+		// Recognized but intentionally not rendered here: router.response is
+		// superseded by chat.turn events on the global stream, and protocol_error is
+		// a transport diagnostic. Explicit no-op so the default below means *unknown*.
+	default:
+		// Unknown-event raw fallback (TUI-requirements §2): a session-scoped event
+		// type this client doesn't recognize is surfaced as a raw row in the event
+		// stream, never silently dropped — the frontend must not lie by omission.
+		if msg.SessionID != "" {
+			s := m.ensureSession(msg.SessionID)
+			at := msg.OccurredAt
+			if at == 0 {
+				at = nowMillis()
+			}
+			s.addEvent(at, msg.Type, "(raw — unrendered event)")
+		}
 	}
 
 	// Background-update badge for non-selected sessions.

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

@@ -0,0 +1,64 @@
+package app
+
+import (
+	"testing"
+
+	"github.com/correx/tui-go/internal/protocol"
+)
+
+func TestAgoLabel(t *testing.T) {
+	cases := []struct {
+		ms   int64
+		want string
+	}{
+		{-100, "0s ago"},
+		{0, "0s ago"},
+		{3_000, "3s ago"},
+		{59_000, "59s ago"},
+		{90_000, "1m ago"},
+		{3_600_000, "1h ago"},
+		{90_000_000, "1d ago"},
+	}
+	for _, c := range cases {
+		if got := agoLabel(c.ms); got != c.want {
+			t.Errorf("agoLabel(%d) = %q, want %q", c.ms, got, c.want)
+		}
+	}
+}
+
+// An event type this client doesn't recognize must still surface as a raw row in the
+// session's event stream — never silently dropped (TUI-requirements §2).
+func TestUnknownEventSurfacesAsRawRow(t *testing.T) {
+	m := NewModel(nil)
+	m.applyServer(protocol.ServerMessage{
+		Type:       "some.future.event",
+		SessionID:  "s1",
+		OccurredAt: 1_700_000_000_000,
+	})
+
+	s := m.session("s1")
+	if s == nil {
+		t.Fatalf("unknown event did not vivify its session")
+	}
+	if len(s.Events) != 1 {
+		t.Fatalf("expected 1 raw event row, got %d", len(s.Events))
+	}
+	if s.Events[0].Type != "some.future.event" {
+		t.Errorf("raw row type = %q, want the unknown type verbatim", s.Events[0].Type)
+	}
+}
+
+// router.response is recognized-but-intentionally-not-rendered on the global stream;
+// it must NOT be misclassified as an unknown event and spawn a spurious row.
+func TestKnownIgnoredEventDoesNotSpawnRow(t *testing.T) {
+	m := NewModel(nil)
+	m.applyServer(protocol.ServerMessage{
+		Type:      protocol.TypeRouterResponse,
+		SessionID: "s1",
+		Content:   "superseded by chat.turn",
+	})
+
+	if len(m.sessions) != 0 {
+		t.Fatalf("router.response should not vivify a session, got %d", len(m.sessions))
+	}
+}

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

@@ -13,6 +13,10 @@ const (
 	statusH = 1
 	footerH = 1
 	inputH  = 4 // rounded box: 2 borders + 2 content lines
+
+	// staleEventThresholdMs: past this gap since the last event, an *active* session's
+	// last-event clock turns warn-colored — the "thinking vs hung" tell (§2).
+	staleEventThresholdMs = 30_000
 )
 
 // View renders the whole frame purely from the model (immediate-mode).
@@ -93,6 +97,17 @@ func (m Model) renderStatus() string {
 	left := strings.Join(parts, sep)
 
 	var right []string
+	// Last-event clock (§2): always visible in-session, so a silent agent is never
+	// mistaken for a healthy one. Updates every frame tick; turns warn-colored when an
+	// active session has gone quiet past the stale threshold.
+	if s := m.session(m.selectedID); s != nil && m.displayState() != StateIdle {
+		gap := nowMillis() - s.LastEventAt
+		clockFg := t.P.Faint
+		if s.Active && gap > staleEventThresholdMs {
+			clockFg = t.P.Warn
+		}
+		right = append(right, span("last event "+agoLabel(gap), clockFg))
+	}
 	if g := m.gaugeText(); g != "" {
 		right = append(right, span(g, t.P.Faint))
 	}
@@ -126,6 +141,26 @@ func (m Model) gaugeText() string {
 	return strings.Join(parts, " ")
 }
 
+// agoLabel renders a millisecond age as a compact "Ns ago" / "Nm ago" / "Nh ago" /
+// "Nd ago". Drives the last-event clock (§2) — the live signal that distinguishes a
+// thinking agent from a hung one.
+func agoLabel(deltaMs int64) string {
+	if deltaMs < 0 {
+		deltaMs = 0
+	}
+	s := deltaMs / 1000
+	switch {
+	case s < 60:
+		return itoa(int(s)) + "s ago"
+	case s < 3600:
+		return itoa(int(s/60)) + "m ago"
+	case s < 86400:
+		return itoa(int(s/3600)) + "h ago"
+	default:
+		return itoa(int(s/86400)) + "d ago"
+	}
+}
+
 var spinnerFrames = []string{"⠋", "⠙", "⠹", "⠸", "⠼", "⠴", "⠦", "⠧", "⠇", "⠏"}
 
 func (m Model) spinner() string { return spinnerFrames[m.frame%len(spinnerFrames)] }