ruby, 90 bytes

Result

AC

Duration

2196ms

Code [DL]

s=`dd`
i=s[/^ *K/].size
s.gsub!(/^ {#{i-1}}\K /,?#)
s.gsub!(/# *(?=T)/){?#*$&.size}
puts s

stdin

                                           T      
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
            K                                     

stdout

            ###############################T      
            #                                     
            #                                     
            #                                     
            #                                     
            #                                     
            #                                     
            #                                     
            #                                     
            #                                     
            #                                     
            #                                     
            #                                     
            #                                     
            #                                     
            #                                     
            #                                     
            #                                     
            #                                     
            #                                     
            #                                     
            #                                     
            K                                     

stderr

2+1 records in
2+1 records out

strace

10    execve("/bin/sh", ["/bin/sh", "/root/script", "/volume/CODE"], 0x7ffe60635c50 /* 9 vars */) = 0
12    execve("/usr/local/ruby-2.6.3/bin/ruby", ["/usr/local/ruby-2.6.3/bin/ruby", "/volume/CODE"], 0x559919fbed60 /* 9 vars */ <unfinished ...>
11    execve("/bin/cat", ["cat", "-"], 0x559919fbed40 /* 9 vars */) = 0
11    +++ exited with 0 +++
10    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=11, si_uid=0, si_status=0, si_utime=0, si_stime=0} ---
12    <... execve resumed> )            = 0
13    execve("/bin/dd", ["dd"], 0x55bb5ba3e2e0 /* 9 vars */) = 0
13    +++ exited with 0 +++
12    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=13, si_uid=0, si_status=0, si_utime=0, si_stime=0} ---
12    +++ exited with 0 +++
10    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=12, si_uid=0, si_status=0, si_utime=8, si_stime=4} ---
10    +++ exited with 0 +++