Currently Xdebug does not accept break command while
the language engine is running.

I guess that the main reason of it is performance.
Checking in-comming command on every statement execution
is too expensive. May be my guess is wrong.

So, how about checking in-comming (break) command every
100 (or 255, whatever) statements execution.

static unsigned char counter = 0;
if (++counter == 0)
{
/ check for incomming break/status command /
...
}

This way, performance down should not be so bad, and
at least I can break the target execution from debugger
client without restarting Apache ;-)