A fix has been pushed:

https://github.com/lalbornoz/tcl/commit/7249454d27938a9834bb4068d2994fdd98c24605

With the patch:
bll-tecra:bll$ time $HOME/local87/bin/tclsh8.7 t.tcl
^C

real    0m7.413s
user    0m0.029s
sys     0m0.005s

dbus test:
bll-tecra:bll$ ps -f -t pts/1 -o pcpu,args
%CPU COMMAND
 0.0 bash
 0.0  \_ rlwrap /home/bll/local87/bin/tclsh8.7

I don't have a specific test for the disconnected socket, but I tested with an older version of my application and it seems fine.