Function default_backend_factory 

pub fn default_backend_factory(feral_cfg: FeralConfig) -> LinearBackendFactory

Default symmetric linear-solver factory, parameterized by the pounce-extension FERAL knobs read off the application’s OptionsList.

FERAL (pure-Rust) is the shipping default. The HSL MA57 backend is available when the ma57 cargo feature is enabled; without it, requesting linear_solver = ma57 falls back to FERAL with a warning printed by the journalist (see AlgorithmBuilder).