I'm assuming this doesn't change anything with respect to the transition, but upon further investigation in gdb the segfault actually seems to be a packaging issue with webdis. Seems like upstream webdis vendors hiredis and jansson. In the Debian packaging we're correctly trying to use the .so, but the #include directives are picking up the vendored headers instead of the headers from libhiredis-dev/libjansson-dev. Thus structs have different layouts in the .so vs the webdis binary and things get weird.
I'll raise a bug with the webdis maintainer to get this addressed.
Cheers,
Tom