Currently a breakpoint specified as relativefilepath:lineno will match only if the relative file path is a simple file name or if sandbox root + relative file path is an exact match. This is now generalized so that matching occurs if the relative file path is a suffix (path) of the absolute path of the execution location.
The debugger client now accepts feedback from the the debugger server about whether a breakpoint can be hit, absent further loads of files, classes or functions.