[plt-scheme] precise GC example?

Hello all:

I'm in the process of converting some C code I used to extend an old
version of mzscheme into a dylib with which to extend an up-to-date
version.  I'm trying to teach the new code how to cooperate with the 3m
GC system, and it's pretty slow going, and I don't have high confidence
that I'm doing it right.

I've already read in the list archives about a way to get around a
"suspicious arithmetic" error using the GC_CAN_IGNORE flag, so that's
one roadblock skirted, perhaps.

I wonder, though, if anyone has a more elaborate example of the genre
to share than the one in collects/mzscheme/example.  I'd be particularly
grateful as well for an example that worked via the mzc --xform compile.

I also wonder about testing.  With GC issues, I'm thinking that merely
working isn't a particularly good test.  How can I be sure that I've
done this correctly and that I'm not merely creating opportunities for
obscure failures at random times in the future?

Many thanks in advance for any advice on these matters anyone would like
to offer.

Happy Lang Syne to all of you.

 -tom

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