[plt-scheme] Are web cells space-safe?

Hello,

I recently implemented web cells [*] for SISCweb, a web "framework"
for the JVM-based SISC scheme.

I would like to confirm that I have a correct understanding of the
space properties of web cells. Right now, from reading the paper and
studying PLT's implementation, I suspect that they allocate space
linearly with the length of the direct navigation path from the first
to the most current continuation.

In particular, I understand that frames in this path are never
dereferenced and garbage collected. In fact, I can see this should not
never happen since a continuation may hold a cell which received its
last value many frames before.

The only way I could see frames being dereferenced without breaking
the program would be if cells belonging to a frame soon to be
destroyed were propagated to the immediate child frames (excluding
cells that exist there already).

Am I missing something? I really would like to include this feature in
the next release of SISCweb, but I am somewhat wary of introducing a
potential for misuse or, worse, DoS attacks.

Regards,
___
Alessandro

[*] As in:
www.cs.brown.edu/~sk/Publications/Papers/Published/mk-int-safe-state-web/paper.pdf