//! # `rtx-fsi` — partitioned fluid–structure interaction coupling
//!
//! Fluid and structure solvers exist separately in this workspace
//! (`rtx-cfd`, `rtx-fea`) and nothing connects them. This crate is the
//! coupling layer: it moves loads from the fluid onto the structure and
//! motion from the structure back onto the fluid, across an interface
//! where the two meshes do **not** match — which is the normal case and
//! the source of most fluid–structure interaction errors.
//!
//! # Why the coupling is worth building separately
//!
//! The properties that make a partitioned coupling correct are testable
//! **independently of whether the solvers it couples are accurate**.
//! Conservation of force, moment and interface work are statements about
//! the transfer operators alone. So this crate can be validated now, on
//! solvers whose canonical-benchmark validation is still outstanding.
//!
//! It therefore depends on neither `rtx-cfd` nor `rtx-fea`. It takes
//! geometry and field values, and returns field values. Adapters to the
//! concrete solvers belong above it.
//!
//! # Scope, stated up front
//!
//! The **transfer operators** (`transfer`) are a small-displacement
//! formulation: interface velocity applied to the fluid through a
//! boundary condition, valid while displacements are small relative to a
//! cell. The **coupling driver** (`coupling`) carries no such limit — it
//! iterates whatever pass the adapter provides, and
//! `tests/piston_added_mass.rs` drives it against `rtx-cfd`'s moving-mesh
//! ALE solver (which owns the Discrete Geometric Conservation Law) at an
//! added-mass ratio of 6.25, reproducing the staggered divergence and the
//! Aitken recovery against a closed-form coupled frequency. Large motion
//! of complex geometry still wants a body-fitted unstructured ALE or an
//! embedded boundary treatment; that decision lives with the solvers, not
//! here.

#![forbid(unsafe_code)]

mod coupling;
mod error;
mod smoothing;
mod transfer;

pub use coupling::{Converged, IqnIls, Subiterated};
pub use error::FsiError;
pub use smoothing::smooth_tractions;
pub use transfer::{FluidFace, WettedSurface};