no, the app isn't frozen (thinking about the Hunchentoot web server).

Also of course the default is to not get the debugger but let the server thread crash and print the backtrace. With a user setting, you can choose to get the debugger, and have this request wait (the connection may time out, which isn't an issue during development). Another setting is to print the backtrace in the browser (= dev mode).

I mean, that entirely depends on the server design. Is it running one connection per process? One connection per thread? Presumably you've designed the server in a way that one slow connection doesn't block other connections from being handled fast, which means that this one connection whose handler went into the debugger is just now a really, really slow connection taking minutes (or hours!) to handle, but the other connections are running just fine.

Now, if your entire server is taken down because one connection threw an exception, that's bad design. But pretty much no major language works that way. All of them allow you to set things up so that an exception handling connection A won't affect connection B. And if you've done that in Common Lisp, then connection A halting and waiting for the debugger won't affect connection B either.