the problem is in your definition of 'end' and 'bottom'

??
end := end of run
bottom := bottom of last page, in this case

 

the real final thing is \end and \everygoodbye happens just before that (the only calls after it are postponed error messages, which have no consequence for any pdf and the primitive \end which is really needed)

yes, as I seen  in \def\stoptext 

of course there can be pending conditional branches that needs to be finished; just try \appendtoks\tracingall\to\everygoodbye

true
 

You can also do something

\startluacode
   table.insert(input.stop_actions, function()
       texio.write_nl("I still have no clue why you need it.")
   end)
\stopluacode

 ok thank you -- I like lua code  --

 

any other hook in itself will introduce a new situation of 'something done before the real \end'

exactly what I mean:

"any other hook in itself will introduce a new situation of 'something done before the real \end'"

that potentially can modify current page .

Consider this:
between

final_cleanup; {prepare for death}

and

end_of_TEX: close_files_and_terminate;

insert
{************* MY HACK ************}
almost_death ;{I see state, but it's  'frozen' so any modification  will never influence  pdf or dvi , only to log or terminal or external files}
{*******************************************}

in   almost_death you can do what ever you want -- you will never modify  (relevant part of ) state
that can influence final pdf or dvi .

==================================================

@ Now this is really it: \TeX\ starts and ends here.

The initial test involving |ready_already| should be deleted if the
\PASCAL\ runtime system is smart enough to detect such a ``mistake.''
@^system dependencies@>

@p begin @!{|start_here|}
history:=fatal_error_stop; {in case we quit during initialization}
t_open_out; {open the terminal for output}
if ready_already=314159 then goto start_of_TEX;
@<Check the ``constant'' values...@>@;
if bad>0 then
  begin wterm_ln('Ouch---my internal constants have been clobbered!',
    '---case ',bad:1);
@.Ouch...clobbered@>
  goto final_end;
  end;
initialize; {set global variables to their starting values}
@!init if not get_strings_started then goto final_end;
init_prim; {call |primitive| for each primitive}
init_str_ptr:=str_ptr; init_pool_ptr:=pool_ptr; fix_date_and_time;
tini@/
ready_already:=314159;
start_of_TEX: @<Initialize the output routines@>;
@<Get the first line of input and prepare to start@>;
history:=spotless; {ready to go!}
@<Initialize synctex primitive@>
main_control; {come to life}

final_cleanup; {prepare for death}

{************* MY HACK ************}
almost_death ;{I see state, but it's  'frozen' so any modification  will never influence  pdf or dvi , only to log or terminal or external files}
{*******************************************}

end_of_TEX: close_files_and_terminate;
final_end: ready_already:=0;
end.

=======================================


anyway,  as I wrote , this is not bad:

\def\LuigisWhateverShouldHappen{\immediate\write16{BOOOM!}Something
Luigi want to do for some unknown reason.\immediate\write16{BOOOM!}}