Initial release: a portable Stan-backend layer that a Stan-based R package can fit its models through, using either rstan (default) or, optionally, cmdstanr.
stan_options() collects and validates sampler options
for the chosen backend, forwarding them verbatim and guarding against
mixing one backend’s argument vocabulary into the other.fit_model() dispatches a fit to the backend recorded on
the options and resolves the calling package’s compiled model
automatically.backend_draws_array(),
backend_extract(),
backend_generate_quantities(), and
backend_has_draws().use_flexstanr() wires flexstanr into a host package’s
DESCRIPTION.requireNamespace() guards; rstan is the default and only
hard Stan dependency.