script vs. terminal vs. same line vs. ^C

[jidanni]

Here we see with the same $-, if you put it on the same line, you'll
run it despite ^C...

$ cat file
echo $-; sleep 7; echo BOOM
$ bash -i file
bhimBC
^C
$ echo $-; sleep 7; echo BOOM
bhimBC
^C
BOOM

OK, same $-, and same test -t <whatever>, so what does one have to do
to make bash think it is a script and not go BOOM, unset PS1 or something?