v := ctx.Value(TraceParamsKey{})
	// Should match SingleHandler.Call checks.
	switch typed := v.(type) {
	case *MSS:
		trace.Path += typed.ToQuery()
	case map[string]string:
		m := MSS(typed)
		trace.Path += m.ToQuery()
	case *URLValues:
		trace.Path += typed.Values().Encode()
	case *NoPayload, *Bytes:
		trace.Path = fmt.Sprintf("%s?payload=%T", trace.Path, typed)
	case string: