It's not a redirect to a file. Fuse calls the 'read' function on the
class, the read function does a 'return' of the data, and fuse passes
the data up through the OS layer to be the result of the 'read' call
made by less.
If you don't know what a fuse file system is, this all gets very confusing
I'm afraid we are getting beyond my level of fuse-foo here. You'd
probably be better off finding a fuse or even fuse-python mailing list
and trying there.
If it were me, I'd start logging everything I could (take a look at
Python's 'logging' module to help you make that easy), and twidling
things. What happens if you change what gets returned to lstat?
What happens for various sizes and contents of the '0' file? What
happens if you use 'cat -v' or hexdump instead of less to read the file?
Run experiments until you gather enough clues to make a guess as to what
is going on, then test your theory. Repeat until success