Fix styled switch-back repaint

internal/vt/emulator.go

@@ -45,6 +45,12 @@ type Emulator interface {
 	// frame" for newly-attached clients.
 	SerializeVT() ([]byte, error)
 
+	// StyledScreenVT returns the active screen's visible cell grid as VT
+	// bytes with SGR styling and child-space cursor movement, but without
+	// terminal modes, scroll regions, tabstops, or formatter cursor side
+	// effects.
+	StyledScreenVT() ([]byte, error)
+
 	// Cursor returns cursor position and visibility on the active screen.
 	Cursor() (CursorState, error)