Our OCaml libs and utilities currently use the pcre OCaml package. That package is based on the original PCRE library. Its latest release 8.45 is the last release and the original implementation is now declared EOL. That package is named libpcre3 in Debian, for some reason.

PCRE maintainers made a new release line called PCRE2 that has now replaced the original. Debian Trixie no longer includes the original implementation, only PCRE2. The package is called libpcre2. Yes, you read it right: libpcre2 is newer than libpcre3.

There are already OCaml bindings for PCRE2 — they are API-compatible, just use a different module name, so we only need to update those names and dependencies to make it work.