python3, 121 bytes

Result

WA

Duration

1206ms

Code [DL]

s=input()
n=s.index("T")
print(s)
while 1:
 print(s)
 t=input()
 try:
  m=t.index("K")
  s=t[:m]+"K"*(n-m+1)
 except:pass

stdin

                           T                      
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
        K                                         

stdout

                           T                      
                           T                      
                           T                      
                           T                      
                           T                      
                           T                      
                           T                      
                           T                      
                           T                      
                           T                      
                           T                      
        KKKKKKKKKKKKKKKKKKKK

stderr

Traceback (most recent call last):
  File "/volume/CODE", line 6, in <module>
    t=input()
EOFError: EOF when reading a line

strace

10    execve("/bin/sh", ["/bin/sh", "/root/script", "/volume/CODE"], 0x7fffac883290 /* 7 vars */) = 0
12    execve("/usr/bin/python3", ["/usr/bin/python3", "/volume/CODE"], 0x55793d16bd50 /* 7 vars */ <unfinished ...>
11    execve("/bin/cat", ["cat", "-"], 0x55793d16bd38 /* 7 vars */ <unfinished ...>
12    <... execve resumed> )            = 0
11    <... 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} ---
12    +++ exited with 1 +++
10    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=12, si_uid=0, si_status=1, si_utime=2, si_stime=1} ---
10    +++ exited with 1 +++