I don't see anything wrong. (That's what I call "a statement of ignorance.")
Have you looked to see if the file, (which is created as a randomly named file in the process's current directory), is present and modified while the editor is open, after a save but before quitting? (It is automatically deleted after editor terminates and the edit() function has sucked its content, so you must look at the right time. It will be a recently created file.)
Have your tried using 'TextEdit' in place of 'BBEdit'?
I do not have BBEdit on my Macs because they are headless, so I am not prepared to do repro on this. I can say that edit() works fine on Windows and Linux. You might try using edit('notes', 'vi') (or some other not-overly-clever editor.) If you do, please report what happens.
(2.1 amendment:)
FWIW, the edit('', 'mg') function works fine as an insert value on my Mac mini running the last OS X version 10.?. The mg editor is findable on my $PATH and knows how to edit, in place<sup><b>1</b></sup>, a file named as its 1st argument.
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<b>1.</b> In-place editing can sometimes be important. There are editors that play games with file names as part of keeping a backup. If more than one process was involved in running an editor, this could interact badly with how edit() works.