fix(tui): repaint fully while scrolling chat

internal/agent/modes/interactive.go

@@ -530,6 +530,13 @@ func (i *Interactive) scrollBy(delta int) {
 		i.parkedTurn = 0
 		i.parkedTotal = 0
 	}
+	if i.rend != nil {
+		// VS Code's terminal is especially prone to leaving stray
+		// wrapped-character fragments behind during scroll-driven
+		// viewport changes. Force a full repaint on scroll, but
+		// avoid a whole-screen clear because that visibly flickers.
+		i.rend.Invalidate()
+	}
 	i.mu.Unlock()
 	i.invalidate()
 }
@@ -540,6 +547,9 @@ func (i *Interactive) scrollToBottom() {
 	i.scrollOffset = 0
 	i.parkedTurn = 0
 	i.parkedTotal = 0
+	if i.rend != nil {
+		i.rend.Invalidate()
+	}
 	i.mu.Unlock()
 	i.invalidate()
 }

internal/tui/render.go

@@ -62,6 +62,13 @@ func (r *Renderer) Clear() {
 	_, _ = io.WriteString(r.out, SeqClearScreen)
 }
 
+// Invalidate forces a full repaint on the next Draw without clearing the
+// whole terminal first. Useful when the cached diff is unreliable but a
+// visible full-screen flash would be too distracting.
+func (r *Renderer) Invalidate() {
+	r.prev = nil
+}
+
 // Draw updates the terminal so that the visible frame ends with the
 // given lines (bottom-aligned). cursorRow/cursorCol are offsets within
 // the lines slice indicating where to place the terminal cursor; use