What's the usage of jobresize?

Question

As title. I'm learning Neovim's terminal-emulator related API. To explain the problem I need to show you the code first. I have a Lua script like this:

local win = vim.api.nvim_get_current_win()
local buf = vim.api.nvim_create_buf(true, false)
local jobid

local chan = vim.api.nvim_open_term(buf, {
  on_input = function(_, _, _, data)
    if jobid then
      pcall(vim.api.nvim_chan_send, jobid, data)
    end
  end,
})

local opts = {
  -- height = vim.api.nvim_win_get_height(win),
  height = 10,
  -- width = true and 2 or vim.api.nvim_win_get_width(win),
  width = 20,
  pty = true,
  on_stdout = function(_, data)
    vim.api.nvim_chan_send(chan, table.concat(data, "\n"))
  end,
  on_exit = function(_, exit_code)
    vim.api.nvim_chan_send(chan, '\r\n[Process exited ' .. tostring(exit_code) .. ']')
    vim.api.nvim_buf_set_keymap(buf, "t", "<CR>", "<cmd>bd!<CR>", { noremap = true, silent = true})
  end,
}

jobid = vim.fn.jobstart({ 'cat', '/path/to/this/test.lua' }, opts)
vim.fn.jobresize(jobid, 20, 10)
vim.fn.jobresize(jobid, 30, 20)
vim.fn.jobresize(jobid, 40, 30)
vim.api.nvim_set_current_buf(buf)

And the three calls of vim.fn.jobresize doesn't seem to change the width and height of the output being printed. I still got a much large width being used after running the script by :source:

• As you can see from the image, it wraps at columns 85, and this is apparently not either 20,30,40 I have set using jobresize.