RenderText only refreshes when window 's expand/collapse button is pressed

[Phm]

I've been trying to code a shiny app that would let you crop an image (only height & with magick package) and being able to dipslay the height at the same time you move the crop slider button.
But as far as I have been working on it (one week ) and tried many things (read many things as well), I still couldn't get better than the code below.
It renders the size but only when the top right hand corner expand/diminish button of the window is pressed.
My code comes from the example from Mr.Jeroen here https://github.com/jeroen/shinymagick/blob/master/app.R

library(shiny)
# Minimal example of Shiny widget using 'magick' images
ui <- fluidPage(
  titlePanel("Magick Shiny Demo"),
  
  sidebarLayout(
    
    sidebarPanel(
      
      fileInput("upload", "Upload new image", accept = c('image/png', 'image/jpeg')),
      textInput("size", "Size", value = "500x500!"),
      h4("Height"),
      verbatimTextOutput("clientdataText"),
      sliderInput("rotation", "Rotation", 0, 360, 0),
      sliderInput("cropw", "Crop width", -1000, 1000, 1, 1),
      sliderInput("croph", "Crop height", -1000, +1000, 1, 1)
      
    ),
    mainPanel(
      imageOutput("img" ,width = "100%", height = "100%", fill =FALSE)
    )
  )
)

server <- function(input, output, session) {
  
  library(magick)
  
  # Start with placeholder img
  image <- image_read("https://raw.githubusercontent.com/ThinkR-open/collage/master/inst/tigrou/tigrou.jpg")
  
  
  # When uploading new image
  observeEvent(input$upload, {
    if (length(input$upload$datapath))
      image <<- image_convert(image_read(input$upload$datapath), "jpeg")
    info <- image_info(image)
    
    updateTextInput(session, "size", value = paste0(info$width, "x", info$height, "!"))
  })
  
  
  
  # A plot of fixed size
  output$img <- renderImage({
    
    # Numeric operators
    tmpfile <- image %>%
      image_resize(input$size) %>%
      image_rotate(input$rotation) %>%
      image_crop(geometry = geometry_point(input$cropw, input$croph), gravity = NULL, repage = TRUE) %>%
      image_write(tempfile(fileext='jpg'), format = 'jpg')
    
    
    # Return a list
    list(src = tmpfile, contentType = "image/jpeg")
  },deleteFile = TRUE)
  
  # Store in a convenience variable
  valueh<-reactive(session$clientData$output_img_height)
  
  # Values from cdata returned as text
  output$clientdataText <- renderText(
    valueh()
  )
}

shinyApp(ui, server)