I'm too behind in my XPages project to think about how I can save time :-/ but when I get some breathing room I'm going to look at Medusa.

Until then, I took a technique I saw from Tommy Valand (emailing a stack trace) and changed/extended it to instead create and populate requestScope.debugOutput.  I create a computed field that is bound to requestScope.debugOutput (using JavaScript so that it's one way instead of binding to requestScope through EL), and then I use the following script library:

Debug = {
    _log : function (msgType, msgSource, msg) {
        var tmp = msgType;
        if (msgSource) {
            tmp += ' from ' + msgSource;
        }
        var newEntry = '<dt>' + @Now() + ' ' + tmp + ':</dt><dd>' + msg + '</dd>';
        if ( requestScope.debugOutput ) {
            requestScope.debugOutput += newEntry;
        } else {
            requestScope.debugOutput = newEntry;
        }
    },
   
    exception : function (exception, source) {
        var stringWriter = new java.io.StringWriter();
        exception.printStackTrace( new java.io.PrintWriter( stringWriter ) );
        this._log('Error', source, stringWriter.toString());
    },
   
    message : function (msg, source) {
        this._log('Print ', source, msg);
    }
};

From within a custom control's combobox's onblur SSJS, I might do something like:

var sHere = 'ccCustomControlName.comboBoxId.onblur';
try {

     Debug.message('starting', sHere);
    // do stuff
     Debug.message('successful', sHere);
} catch (e) {

     Debug.exception(e, sHere);
}

 

Two caveats:

1. It appears that you can't use global variables that don't exist, so when you remove the Debug script library from your XPages, you also have to remove all the calls.  Even code like "if ( Debug ) { Debug.exception(e, sHere); }" will crash if Debug doesn't exist.
   
2. If you're debugging partial refreshes then your display of requestScope.debugOutput must be within what you're refreshing.