Autocmd commands for sharing terminal when open new tab

Question

I was trying to create a trigger that does the following: When opening a new tab with a file, if there already exists a terminal buffer, it is opened below in this new tab.

I have seen in logfiles that the events triggered when opening a new tab are WinLeave, TabLeave, WinEnter and TabEnter (in this order). In my .vimrc file I created an augroup and tried to use autocmds.

The problem is that it does not work as expected (it does nothing, actually), and I am pretty sure that the wrong part is related to sequential autocmd.

Here is the code:

    autocmd!
    " Take into account events in their order
    autocmd WinLeave ++nest autocmd TabLeave
        \ ++nest autocmd WinEnter ++nest autocmd TabEnter * |
        " Create variable with existing terminal buffers
        \ let term_buf = filter(range(1, bufnr('$')),
            \ 'getbufvar(v:val, "&buftype", "ERROR") == "terminal"') |
        \ if len(term_buf) > 0 |
            " First terminal buffer taken
            \ let x = term_buf[0] |
            " Open new buffer below
            \ exe 'below sbuffer'.x |
            \ startinsert |
        \ endif
augroup end