ruby, 80 bytes

Result

AC

Duration

937ms

Code [DL]

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

stdin

                                         T        
                                                  
                                  K               

stdout

                                  #######T        
                                  #               
                                  K               

stderr

0+1 records in
0+1 records out

strace

10    execve("/bin/sh", ["/bin/sh", "/root/script", "/volume/CODE"], 0x7ffcc109b6a0 /* 9 vars */) = 0
11    execve("/bin/cat", ["cat", "-"], 0x55b7a426bd40 /* 9 vars */ <unfinished ...>
12    execve("/usr/local/ruby-2.6.3/bin/ruby", ["/usr/local/ruby-2.6.3/bin/ruby", "/volume/CODE"], 0x55b7a426bd60 /* 9 vars */ <unfinished ...>
11    <... execve resumed> )            = 0
12    <... execve resumed> )            = 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} ---
13    execve("/bin/dd", ["dd"], 0x55f48f9a4a20 /* 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=3} ---
10    +++ exited with 0 +++