I had initially assumed that because of the assembly from blake3, the address sanitizer could not be used, but that was silly.

Instead the problem was that -fsanitize=address must be passed both for object compilation and linking, and I had omitted the latter, resulting in a bunch of undefined references at link time.

Meson has some base options [1] that includes b_sanitize. It appears this option can only be set in the default options (or passed as -Db_sanitize=address at configure time) so to build w/o it a project reconfiguration is needed.

[1] https://mesonbuild.com/Builtin-options.html#base-options