pounce_cinterface/

lib.rs

//! POUNCE C ABI — port of `Interfaces/IpStdCInterface.{h,cpp}`.
//!
//! Provides the `CreateIpoptProblem / IpoptSolve / FreeIpoptProblem` C
//! entry points that existing PyIpopt / cyipopt / JuMP wrappers link
//! against. Function names and signatures match upstream Ipopt 3.14.x
//! exactly so consumers can swap `libipopt.{dylib,so}` for
//! `libpounce_cinterface` without rebuilding.
//!
//! Surface area (in `IpStdCInterface.h` order):
//!
//! * Lifecycle: [`CreateIpoptProblem`], [`FreeIpoptProblem`].
//! * Options: [`AddIpoptStrOption`], [`AddIpoptNumOption`],
//!   [`AddIpoptIntOption`], [`OpenIpoptOutputFile`],
//!   [`SetIpoptProblemScaling`].
//! * Callbacks: [`SetIntermediateCallback`].
//! * Solve: [`IpoptSolve`].
//! * Introspection (only valid inside an intermediate callback):
//!   [`GetIpoptCurrentIterate`], [`GetIpoptCurrentViolations`].
//! * Library info: [`GetIpoptVersion`].
//!
//! Pounce extensions for post-solve stats (not present in upstream
//! Ipopt's C API): [`GetIpoptIterCount`], [`GetIpoptSolveTime`],
//! [`GetIpoptPrimalInf`], [`GetIpoptDualInf`], [`GetIpoptComplInf`].
//!
//! All entry points are `extern "C"` and `#[no_mangle]`. Pointers are
//! raw and the caller is responsible for lifetime; the `IpoptProblem`
//! handle is opaque (`*mut c_void` from C's perspective). The Fortran
//! 77 ABI shim lives in [`fortran`].

#![allow(non_camel_case_types, non_snake_case)]
#![allow(unsafe_op_in_unsafe_fn, dead_code)]
#![cfg_attr(test, allow(clippy::unwrap_used, clippy::expect_used))]

pub mod fortran;
pub mod solver;

use pounce_algorithm::application::{
    default_backend_factory, feral_config_from_options, IpoptApplication,
};
use pounce_algorithm::intermediate as ip_intermediate;
use pounce_nlp::return_codes::ApplicationReturnStatus;
use pounce_nlp::solve_statistics::SolveStatistics;
use pounce_nlp::tnlp::{
    BoundsInfo, IndexStyle, IpoptCq, IpoptData, NlpInfo, ScalingRequest, Solution, SparsityRequest,
    StartingPoint, TNLP,
};
use pounce_restoration::resto_alg_builder::RestoAlgorithmBuilder;
use pounce_restoration::resto_inner_solver::{
    make_default_restoration_factory_provider, InnerBackendFactoryFactory,
};
use std::cell::RefCell;
use std::ffi::{c_char, c_int, c_void, CStr};
use std::rc::Rc;

/// Mirrors C `Number` typedef in `IpStdCInterface.h`.
pub type Number = f64;
/// Mirrors C `Index`.
pub type Index = c_int;
/// Mirrors C `Bool`.
pub type Bool = c_int;

const TRUE: Bool = 1;
const FALSE: Bool = 0;

/// Run an FFI entry-point body, converting any Rust panic into `fallback`
/// rather than letting it unwind across the `extern "C"` boundary — which is
/// undefined behavior and, in practice, a process abort that takes the
/// embedding application down with it. Upstream Ipopt's C interface likewise
/// wraps the solve in `try { … } catch(…)` and reports `Internal_Error`
/// instead of propagating a C++ exception across the ABI.
///
/// Note: this guards panics that originate in *pounce's own* Rust code (the
/// solver core, the callback bridge, numerical kernels). A panic inside a
/// user-supplied `extern "C"` callback aborts at that callback's own ABI
/// boundary, before unwinding can reach here — that is the caller's
/// responsibility, exactly as in the C/C++ original.
pub(crate) fn ffi_guard<R>(fallback: R, body: impl FnOnce() -> R) -> R {
    match std::panic::catch_unwind(std::panic::AssertUnwindSafe(body)) {
        Ok(r) => r,
        Err(_) => fallback,
    }
}

/// C-ABI encoding of [`pounce_qp::BoundStatus`] (§7.2 of the
/// active-set-SQP design note). Stable values:
/// `0 = Inactive`, `1 = AtLower`, `2 = AtUpper`, `3 = Fixed`.
pub type IpoptBoundStatus = c_int;
/// C-ABI encoding of [`pounce_qp::ConsStatus`] (§7.2). Stable values:
/// `0 = Inactive`, `1 = AtLower`, `2 = AtUpper`, `3 = Equality`.
pub type IpoptConsStatus = c_int;

const POUNCE_WS_INACTIVE: c_int = 0;
const POUNCE_WS_AT_LOWER: c_int = 1;
const POUNCE_WS_AT_UPPER: c_int = 2;
const POUNCE_WS_FIXED_OR_EQ: c_int = 3;

/// Internal owned state behind the opaque `IpoptProblem` handle.
/// `#[repr(C)]` is unnecessary because C only sees the pointer.
pub struct IpoptProblemInfo {
    pub(crate) app: IpoptApplication,
    pub(crate) n: Index,
    pub(crate) m: Index,
    pub(crate) nele_jac: Index,
    pub(crate) nele_hess: Index,
    pub(crate) index_style: Index,
    pub(crate) x_l: Vec<Number>,
    pub(crate) x_u: Vec<Number>,
    pub(crate) g_l: Vec<Number>,
    pub(crate) g_u: Vec<Number>,
    pub(crate) eval_f: Option<Eval_F_CB>,
    pub(crate) eval_g: Option<Eval_G_CB>,
    pub(crate) eval_grad_f: Option<Eval_Grad_F_CB>,
    pub(crate) eval_jac_g: Option<Eval_Jac_G_CB>,
    pub(crate) eval_h: Option<Eval_H_CB>,
    pub(crate) intermediate_cb: Option<Intermediate_CB>,
    /// User-provided scaling installed by [`SetIpoptProblemScaling`].
    /// `obj_scaling` defaults to `1.0`. `x_scaling`/`g_scaling` are
    /// `None` when the user passed NULL.
    pub(crate) user_scaling: Option<UserScaling>,
    /// Final iterate and stats from the most recent [`IpoptSolve`].
    /// Used by `GetIpopt{IterCount,SolveTime,...}` accessors. Reset
    /// (cleared) by the next `IpoptSolve` call.
    pub(crate) last_solve: Option<LastSolve>,
}

/// User-provided NLP scaling stored on the problem until
/// [`IpoptSolve`] copies it into the [`CCallbackTnlp`] bridge.
#[derive(Clone)]
pub(crate) struct UserScaling {
    obj_scaling: Number,
    x_scaling: Option<Vec<Number>>,
    g_scaling: Option<Vec<Number>>,
}

/// Stats and final-iterate snapshot retained between
/// [`IpoptSolve`] and the post-solve accessors. Everything needed to
/// reconstruct a `pounce.solve-report/v1` JSON file lives here so
/// [`IpoptWriteSolveReport`] doesn't have to ask the caller to thread
/// `x`/`lambda`/`obj` back in.
#[derive(Clone)]
pub(crate) struct LastSolve {
    pub(crate) stats: SolveStatistics,
    pub(crate) status: ApplicationReturnStatus,
    pub(crate) linear_solver: Option<pounce_linsol::summary::LinearSolverSummary>,
    pub(crate) final_x: Vec<Number>,
    pub(crate) final_lambda: Vec<Number>,
    pub(crate) final_obj: Number,
}

impl Default for LastSolve {
    fn default() -> Self {
        Self {
            stats: SolveStatistics::default(),
            status: ApplicationReturnStatus::InternalError,
            linear_solver: None,
            final_x: Vec::new(),
            final_lambda: Vec::new(),
            final_obj: 0.0,
        }
    }
}

pub type IpoptProblem = *mut IpoptProblemInfo;

// User-callback function pointer types — match
// `IpStdCInterface.h:Eval_F_CB` etc. byte for byte.

pub type Eval_F_CB = unsafe extern "C" fn(
    n: Index,
    x: *const Number,
    new_x: Bool,
    obj_value: *mut Number,
    user_data: *mut c_void,
) -> Bool;

pub type Eval_Grad_F_CB = unsafe extern "C" fn(
    n: Index,
    x: *const Number,
    new_x: Bool,
    grad_f: *mut Number,
    user_data: *mut c_void,
) -> Bool;

pub type Eval_G_CB = unsafe extern "C" fn(
    n: Index,
    x: *const Number,
    new_x: Bool,
    m: Index,
    g: *mut Number,
    user_data: *mut c_void,
) -> Bool;

pub type Eval_Jac_G_CB = unsafe extern "C" fn(
    n: Index,
    x: *const Number,
    new_x: Bool,
    m: Index,
    nele_jac: Index,
    iRow: *mut Index,
    jCol: *mut Index,
    values: *mut Number,
    user_data: *mut c_void,
) -> Bool;

pub type Eval_H_CB = unsafe extern "C" fn(
    n: Index,
    x: *const Number,
    new_x: Bool,
    obj_factor: Number,
    m: Index,
    lambda: *const Number,
    new_lambda: Bool,
    nele_hess: Index,
    iRow: *mut Index,
    jCol: *mut Index,
    values: *mut Number,
    user_data: *mut c_void,
) -> Bool;

pub type Intermediate_CB = unsafe extern "C" fn(
    alg_mod: Index,
    iter_count: Index,
    obj_value: Number,
    inf_pr: Number,
    inf_du: Number,
    mu: Number,
    d_norm: Number,
    regularization_size: Number,
    alpha_du: Number,
    alpha_pr: Number,
    ls_trials: Index,
    user_data: *mut c_void,
) -> Bool;

/// Port of `IpStdCInterface.cpp:CreateIpoptProblem`. Returns NULL on
/// invalid arguments (negative n/m, missing required callbacks, NULL
/// bound pointers when the corresponding dimension is positive).
///
/// # Safety
///
/// `x_L`, `x_U` must be valid pointers to `n` `Number`s when `n > 0`.
/// `g_L`, `g_U` must be valid pointers to `m` `Number`s when `m > 0`.
/// The callback function pointers must be valid for the lifetime of
/// the returned [`IpoptProblem`].
#[no_mangle]
pub unsafe extern "C" fn CreateIpoptProblem(
    n: Index,
    x_L: *const Number,
    x_U: *const Number,
    m: Index,
    g_L: *const Number,
    g_U: *const Number,
    nele_jac: Index,
    nele_hess: Index,
    index_style: Index,
    eval_f: Option<Eval_F_CB>,
    eval_g: Option<Eval_G_CB>,
    eval_grad_f: Option<Eval_Grad_F_CB>,
    eval_jac_g: Option<Eval_Jac_G_CB>,
    eval_h: Option<Eval_H_CB>,
) -> IpoptProblem {
    // Install the tracing subscriber on first use so C consumers
    // (cyipopt, AMPL, …) get logging and the iteration collector that
    // backs `IpoptEnableIterHistory` (pounce#71). Idempotent.
    pounce_observability::init_subscriber();

    if n < 0 || m < 0 || nele_jac < 0 || nele_hess < 0 {
        return std::ptr::null_mut();
    }
    if !(0..=1).contains(&index_style) {
        return std::ptr::null_mut();
    }
    if eval_f.is_none() || eval_grad_f.is_none() {
        return std::ptr::null_mut();
    }
    if m > 0 && (eval_g.is_none() || eval_jac_g.is_none()) {
        return std::ptr::null_mut();
    }
    if n > 0 && (x_L.is_null() || x_U.is_null()) {
        return std::ptr::null_mut();
    }
    if m > 0 && (g_L.is_null() || g_U.is_null()) {
        return std::ptr::null_mut();
    }

    let x_l = if n > 0 {
        std::slice::from_raw_parts(x_L, n as usize).to_vec()
    } else {
        Vec::new()
    };
    let x_u = if n > 0 {
        std::slice::from_raw_parts(x_U, n as usize).to_vec()
    } else {
        Vec::new()
    };
    let g_l_vec = if m > 0 {
        std::slice::from_raw_parts(g_L, m as usize).to_vec()
    } else {
        Vec::new()
    };
    let g_u_vec = if m > 0 {
        std::slice::from_raw_parts(g_U, m as usize).to_vec()
    } else {
        Vec::new()
    };

    let info = Box::new(IpoptProblemInfo {
        app: IpoptApplication::new(),
        n,
        m,
        nele_jac,
        nele_hess,
        index_style,
        x_l,
        x_u,
        g_l: g_l_vec,
        g_u: g_u_vec,
        eval_f,
        eval_g,
        eval_grad_f,
        eval_jac_g,
        eval_h,
        intermediate_cb: None,
        user_scaling: None,
        last_solve: None,
    });
    Box::into_raw(info)
}

/// Port of `IpStdCInterface.cpp:FreeIpoptProblem`.
///
/// # Safety
///
/// `ipopt_problem` must be a pointer previously returned by
/// [`CreateIpoptProblem`] and not yet freed, or NULL.
#[no_mangle]
pub unsafe extern "C" fn FreeIpoptProblem(ipopt_problem: IpoptProblem) {
    if ipopt_problem.is_null() {
        return;
    }
    drop(Box::from_raw(ipopt_problem));
}

unsafe fn keyword_str<'a>(keyword: *const c_char) -> Option<&'a str> {
    if keyword.is_null() {
        return None;
    }
    CStr::from_ptr(keyword).to_str().ok()
}

/// Port of `IpStdCInterface.cpp:AddIpoptStrOption`.
///
/// # Safety
///
/// `ipopt_problem` must be a valid `IpoptProblem`. `keyword` and `val`
/// must be valid NUL-terminated strings.
#[no_mangle]
pub unsafe extern "C" fn AddIpoptStrOption(
    ipopt_problem: IpoptProblem,
    keyword: *const c_char,
    val: *const c_char,
) -> Bool {
    if ipopt_problem.is_null() {
        return FALSE;
    }
    let info = &mut *ipopt_problem;
    let Some(k) = keyword_str(keyword) else {
        return FALSE;
    };
    if val.is_null() {
        return FALSE;
    }
    let Ok(v) = CStr::from_ptr(val).to_str() else {
        return FALSE;
    };
    match info.app.options_mut().set_string_value(k, v, true, false) {
        Ok(_) => TRUE,
        Err(_) => FALSE,
    }
}

/// Port of `AddIpoptNumOption`.
///
/// # Safety
///
/// `keyword` must be a valid NUL-terminated string and
/// `ipopt_problem` must be a valid `IpoptProblem`.
#[no_mangle]
pub unsafe extern "C" fn AddIpoptNumOption(
    ipopt_problem: IpoptProblem,
    keyword: *const c_char,
    val: Number,
) -> Bool {
    if ipopt_problem.is_null() {
        return FALSE;
    }
    let info = &mut *ipopt_problem;
    let Some(k) = keyword_str(keyword) else {
        return FALSE;
    };
    match info
        .app
        .options_mut()
        .set_numeric_value(k, val, true, false)
    {
        Ok(_) => TRUE,
        Err(_) => FALSE,
    }
}

/// Port of `AddIpoptIntOption`.
///
/// # Safety
///
/// `keyword` must be a valid NUL-terminated string and
/// `ipopt_problem` must be a valid `IpoptProblem`.
#[no_mangle]
pub unsafe extern "C" fn AddIpoptIntOption(
    ipopt_problem: IpoptProblem,
    keyword: *const c_char,
    val: Index,
) -> Bool {
    if ipopt_problem.is_null() {
        return FALSE;
    }
    let info = &mut *ipopt_problem;
    let Some(k) = keyword_str(keyword) else {
        return FALSE;
    };
    match info.app.options_mut().set_integer_value(
        k,
        val as pounce_common::types::Index,
        true,
        false,
    ) {
        Ok(_) => TRUE,
        Err(_) => FALSE,
    }
}

/// Port of `IpStdCInterface.cpp:OpenIpoptOutputFile`. Opens `file_name`
/// at `print_level` and attaches a journalist `FileJournal` so all
/// solver output is mirrored to disk. Equivalent to setting
/// `output_file` + `file_print_level` options and triggering
/// `IpoptApplication::Initialize`.
///
/// Returns `TRUE` (1) on success, `FALSE` (0) if the file could not
/// be opened or the option store rejected the value.
///
/// # Safety
///
/// `ipopt_problem` must be a valid `IpoptProblem`. `file_name` must
/// be a valid NUL-terminated string.
#[no_mangle]
pub unsafe extern "C" fn OpenIpoptOutputFile(
    ipopt_problem: IpoptProblem,
    file_name: *const c_char,
    print_level: c_int,
) -> Bool {
    if ipopt_problem.is_null() || file_name.is_null() {
        return FALSE;
    }
    let info = &mut *ipopt_problem;
    let Ok(fname) = CStr::from_ptr(file_name).to_str() else {
        return FALSE;
    };
    if info.app.open_output_file(fname, print_level) {
        TRUE
    } else {
        FALSE
    }
}

/// Port of `IpStdCInterface.cpp:SetIpoptProblemScaling`. Stores
/// user-provided NLP scaling on the problem; the scaling is forwarded
/// to the solver via [`TNLP::get_scaling_parameters`] when the option
/// `nlp_scaling_method=user-scaling` is set. Passing NULL for
/// `x_scaling` / `g_scaling` disables scaling on that axis.
///
/// Always returns `TRUE`.
///
/// # Safety
///
/// `ipopt_problem` must be a valid `IpoptProblem`. When non-NULL,
/// `x_scaling` must point to `n` doubles and `g_scaling` to `m`
/// doubles; both arrays are copied internally.
#[no_mangle]
pub unsafe extern "C" fn SetIpoptProblemScaling(
    ipopt_problem: IpoptProblem,
    obj_scaling: Number,
    x_scaling: *const Number,
    g_scaling: *const Number,
) -> Bool {
    if ipopt_problem.is_null() {
        return FALSE;
    }
    let info = &mut *ipopt_problem;
    let n = info.n as usize;
    let m = info.m as usize;
    let x_vec = if !x_scaling.is_null() && n > 0 {
        Some(std::slice::from_raw_parts(x_scaling, n).to_vec())
    } else {
        None
    };
    let g_vec = if !g_scaling.is_null() && m > 0 {
        Some(std::slice::from_raw_parts(g_scaling, m).to_vec())
    } else {
        None
    };
    info.user_scaling = Some(UserScaling {
        obj_scaling,
        x_scaling: x_vec,
        g_scaling: g_vec,
    });
    TRUE
}

/// Port of `IpStdCInterface.cpp:IpoptSolve`. Returns the
/// `ApplicationReturnStatus` integer.
///
/// Builds a [`CCallbackTnlp`] from the user-supplied callback table
/// and bounds, runs it through [`IpoptApplication::optimize_tnlp`],
/// and writes back the final iterate.
///
/// # Safety
///
/// All pointer arguments are read/written per the
/// `IpStdCInterface.h` contract: `x` is in/out (size `n`); `g`,
/// `mult_g`, `mult_x_L`, `mult_x_U` are out-only (sizes `m, m, n, n`)
/// and may be NULL when the corresponding output is not desired.
#[allow(clippy::too_many_arguments)]
#[no_mangle]
pub unsafe extern "C" fn IpoptSolve(
    ipopt_problem: IpoptProblem,
    x: *mut Number,
    g: *mut Number,
    obj_val: *mut Number,
    mult_g: *mut Number,
    mult_x_L: *mut Number,
    mult_x_U: *mut Number,
    user_data: *mut c_void,
) -> Index {
    if ipopt_problem.is_null() {
        return ApplicationReturnStatus::InternalError as Index;
    }
    // Invalidate the retained stats up front, before the solve is attempted.
    // The `last_solve` snapshot is only repopulated at the *end* of a
    // completed solve, so if the guarded body below bails early or a panic is
    // caught (returning `Internal_Error`), the post-solve accessors
    // (`GetIpoptIterCount`, `IpoptWriteSolveReport`, …) must not silently
    // report the *previous* solve's stats. Clearing here makes the
    // failure-consistent state "no data" rather than stale data (F5).
    (*ipopt_problem).last_solve = None;
    // Guard the whole solve: `optimize_tnlp` runs the entire pounce core and
    // callback bridge, any of which could panic on an unexpected internal
    // state. Without this, such a panic would unwind across `extern "C"` and
    // abort the embedding process; instead we report `Internal_Error`,
    // matching upstream Ipopt's exception handling. (See `ffi_guard`.)
    ffi_guard(ApplicationReturnStatus::InternalError as Index, || unsafe {
        let info = &mut *ipopt_problem;
        if info.n < 0 || info.m < 0 {
            return ApplicationReturnStatus::InvalidProblemDefinition as Index;
        }
        if info.n > 0 && x.is_null() {
            return ApplicationReturnStatus::InvalidProblemDefinition as Index;
        }

        let n_us = info.n as usize;
        let m_us = info.m as usize;
        let initial_x = if n_us > 0 {
            std::slice::from_raw_parts(x, n_us).to_vec()
        } else {
            Vec::new()
        };

        let bridge = Rc::new(RefCell::new(CCallbackTnlp {
            n: info.n,
            m: info.m,
            nele_jac: info.nele_jac,
            nele_hess: info.nele_hess,
            index_style: info.index_style,
            x_l: info.x_l.clone(),
            x_u: info.x_u.clone(),
            g_l: info.g_l.clone(),
            g_u: info.g_u.clone(),
            initial_x,
            eval_f: info.eval_f,
            eval_grad_f: info.eval_grad_f,
            eval_g: info.eval_g,
            eval_jac_g: info.eval_jac_g,
            eval_h: info.eval_h,
            user_data,
            intermediate_cb: info.intermediate_cb,
            user_scaling: info.user_scaling.clone(),
            final_status: None,
            final_x: vec![0.0; n_us],
            final_z_l: vec![0.0; n_us],
            final_z_u: vec![0.0; n_us],
            final_g: vec![0.0; m_us],
            final_lambda: vec![0.0; m_us],
            final_obj: 0.0,
        }));

        // Wire the restoration phase fresh for this solve. Without it, any
        // line-search failure surfaces as `RestorationFailure` instead of
        // falling back into the ℓ1-feasibility sub-IPM — exactly what the
        // CLI driver does. Re-wire per `IpoptSolve` to stay correct across
        // repeated solves on the same `IpoptProblem`. The feral config is
        // snapshot from the now-fully-populated options so `feral_*`
        // overrides flow into the restoration sub-IPM too. Use the multi-pass
        // provider so the ℓ₁ wrapper / auto-fallback don't panic on the
        // second inner solve (pounce#10 Phase 3 / pounce#24).
        let feral_cfg = feral_config_from_options(info.app.options());
        let bff_mint = move || -> InnerBackendFactoryFactory {
            let feral_cfg = feral_cfg.clone();
            Box::new(move || default_backend_factory(feral_cfg.clone()))
        };
        let resto_provider = make_default_restoration_factory_provider(
            RestoAlgorithmBuilder::new(),
            info.app.algorithm_builder_from_options(),
            bff_mint,
        );
        info.app.set_restoration_factory_provider(resto_provider);

        let bridge_for_solve: Rc<RefCell<dyn TNLP>> = bridge.clone();
        let status = info.app.optimize_tnlp(bridge_for_solve);
        let bridge_ref = bridge.borrow();
        info.last_solve = Some(LastSolve {
            stats: info.app.statistics(),
            status,
            linear_solver: info.app.linear_solver_summary(),
            final_x: bridge_ref.final_x.clone(),
            final_lambda: bridge_ref.final_lambda.clone(),
            final_obj: bridge_ref.final_obj,
        });
        if !x.is_null() && n_us > 0 {
            std::ptr::copy_nonoverlapping(bridge_ref.final_x.as_ptr(), x, n_us);
        }
        if !g.is_null() && m_us > 0 {
            std::ptr::copy_nonoverlapping(bridge_ref.final_g.as_ptr(), g, m_us);
        }
        if !obj_val.is_null() {
            *obj_val = bridge_ref.final_obj;
        }
        if !mult_g.is_null() && m_us > 0 {
            std::ptr::copy_nonoverlapping(bridge_ref.final_lambda.as_ptr(), mult_g, m_us);
        }
        if !mult_x_L.is_null() && n_us > 0 {
            std::ptr::copy_nonoverlapping(bridge_ref.final_z_l.as_ptr(), mult_x_L, n_us);
        }
        if !mult_x_U.is_null() && n_us > 0 {
            std::ptr::copy_nonoverlapping(bridge_ref.final_z_u.as_ptr(), mult_x_U, n_us);
        }
        status as Index
    })
}

/// Port of `SetIntermediateCallback`.
///
/// # Safety
///
/// `ipopt_problem` must be valid.
#[no_mangle]
pub unsafe extern "C" fn SetIntermediateCallback(
    ipopt_problem: IpoptProblem,
    intermediate_cb: Option<Intermediate_CB>,
) -> Bool {
    if ipopt_problem.is_null() {
        return FALSE;
    }
    let info = &mut *ipopt_problem;
    info.intermediate_cb = intermediate_cb;
    TRUE
}

/// Port of `IpStdCInterface.cpp:GetIpoptCurrentIterate` (Ipopt 3.14+).
/// Designed to be called from inside an intermediate callback to
/// inspect `x`, the bound multipliers `z_L/z_U`, the constraint values
/// `g`, and the constraint multipliers `lambda` at the current
/// iterate.
///
/// All output buffers are optional — pass NULL to skip. `n` and `m`
/// must match the dimensions the problem was created with; mismatched
/// sizes cause the function to return `FALSE` without writing.
///
/// `scaled` is currently ignored — quantities are reported in the
/// user TNLP's unscaled space (matching upstream Ipopt's default
/// caller behavior when scaling is unused). Honoring `scaled` for the
/// `gradient-based` scaler is a follow-up.
///
/// Returns `FALSE` when called outside an active intermediate
/// callback (no live iterate to inspect).
///
/// # Safety
///
/// `ipopt_problem` must be a valid `IpoptProblem`. Each output buffer,
/// when non-NULL, must hold at least the declared length.
#[allow(clippy::too_many_arguments)]
#[no_mangle]
pub unsafe extern "C" fn GetIpoptCurrentIterate(
    ipopt_problem: IpoptProblem,
    _scaled: Bool,
    n: Index,
    x: *mut Number,
    z_l: *mut Number,
    z_u: *mut Number,
    m: Index,
    g: *mut Number,
    lambda: *mut Number,
) -> Bool {
    if ipopt_problem.is_null() {
        return FALSE;
    }
    let info = &*ipopt_problem;
    if n != info.n || m != info.m {
        return FALSE;
    }
    let result = ip_intermediate::with_current(|ctx| {
        let data = ctx.data.borrow();
        let Some(curr) = data.curr.as_ref() else {
            return false;
        };
        let nlp = ctx.nlp.borrow();
        let n_us = n as usize;
        let m_us = m as usize;
        if !x.is_null() && n_us > 0 {
            let full_x = nlp.lift_x_to_full(&*curr.x);
            if full_x.len() != n_us {
                return false;
            }
            std::ptr::copy_nonoverlapping(full_x.as_ptr(), x, n_us);
        }
        if !z_l.is_null() && n_us > 0 {
            let full = nlp.pack_z_l_for_user(&*curr.z_l);
            if full.len() != n_us {
                return false;
            }
            std::ptr::copy_nonoverlapping(full.as_ptr(), z_l, n_us);
        }
        if !z_u.is_null() && n_us > 0 {
            let full = nlp.pack_z_u_for_user(&*curr.z_u);
            if full.len() != n_us {
                return false;
            }
            std::ptr::copy_nonoverlapping(full.as_ptr(), z_u, n_us);
        }
        if !g.is_null() && m_us > 0 {
            let cq = ctx.cq.borrow();
            let full = nlp.pack_g_for_user(&*cq.curr_c(), &*cq.curr_d());
            if full.len() != m_us {
                return false;
            }
            std::ptr::copy_nonoverlapping(full.as_ptr(), g, m_us);
        }
        if !lambda.is_null() && m_us > 0 {
            let full = nlp.pack_lambda_for_user(&*curr.y_c, &*curr.y_d);
            if full.len() != m_us {
                return false;
            }
            std::ptr::copy_nonoverlapping(full.as_ptr(), lambda, m_us);
        }
        true
    });
    if result.unwrap_or(false) {
        TRUE
    } else {
        FALSE
    }
}

/// Port of `IpStdCInterface.cpp:GetIpoptCurrentViolations` (Ipopt 3.14+).
/// Same contract as [`GetIpoptCurrentIterate`]; returns `FALSE` when
/// called outside an active intermediate callback.
///
/// `scaled` is currently ignored — see [`GetIpoptCurrentIterate`].
/// Violations and complementarities are reported in the compressed
/// algorithm-side space scattered out to full-`n`/`m`; this is the
/// shape upstream callers consume (zero-fill for free positions /
/// no-bound positions).
///
/// # Safety
///
/// `ipopt_problem` must be a valid `IpoptProblem`. Each output buffer,
/// when non-NULL, must hold at least the declared length.
#[allow(clippy::too_many_arguments)]
#[no_mangle]
pub unsafe extern "C" fn GetIpoptCurrentViolations(
    ipopt_problem: IpoptProblem,
    _scaled: Bool,
    n: Index,
    x_l_violation: *mut Number,
    x_u_violation: *mut Number,
    compl_x_l: *mut Number,
    compl_x_u: *mut Number,
    grad_lag_x: *mut Number,
    m: Index,
    nlp_constraint_violation: *mut Number,
    compl_g: *mut Number,
) -> Bool {
    if ipopt_problem.is_null() {
        return FALSE;
    }
    let info = &*ipopt_problem;
    if n != info.n || m != info.m {
        return FALSE;
    }
    let result = ip_intermediate::with_current(|ctx| {
        let data = ctx.data.borrow();
        let Some(_curr) = data.curr.as_ref() else {
            return false;
        };
        drop(data);
        let nlp = ctx.nlp.borrow();
        let cq = ctx.cq.borrow();
        let n_us = n as usize;
        let m_us = m as usize;
        // x_L / x_U violations: scatter the compressed slack-shortfalls
        // up to full-`n`. Upstream defines `x_L_violation_i = max(0, x_L_i
        // - x_i)`; the algorithm tracks `slack_x_l = P_L^T x - x_L`
        // (always non-negative at feasible iterates), so reverse the
        // sign and clamp.
        if !x_l_violation.is_null() && n_us > 0 {
            let slack = cq.curr_slack_x_l();
            let z_l_full = nlp.pack_z_l_for_user(&*slack);
            // Guard the scatter length exactly like the sibling branches
            // below: an unexpected packed length would otherwise index
            // `v[i]` out of bounds and panic across this `extern "C"`
            // boundary (an abort, not a recoverable error).
            if z_l_full.len() != n_us {
                return false;
            }
            // pack_z_l_for_user scatters by the same x_L mapping; the
            // returned vector at full-x positions holds `slack_x_l[i]`
            // which is `x_i - x_L_i`. Clamp the *negative* part to get
            // the violation `max(0, x_L_i - x_i)`.
            let mut v = vec![0.0; n_us];
            for (i, s) in z_l_full.iter().enumerate() {
                v[i] = (-s).max(0.0);
            }
            std::ptr::copy_nonoverlapping(v.as_ptr(), x_l_violation, n_us);
        }
        if !x_u_violation.is_null() && n_us > 0 {
            let slack = cq.curr_slack_x_u();
            let s_full = nlp.pack_z_u_for_user(&*slack);
            if s_full.len() != n_us {
                return false;
            }
            let mut v = vec![0.0; n_us];
            for (i, s) in s_full.iter().enumerate() {
                v[i] = (-s).max(0.0);
            }
            std::ptr::copy_nonoverlapping(v.as_ptr(), x_u_violation, n_us);
        }
        if !compl_x_l.is_null() && n_us > 0 {
            let v = nlp.pack_z_l_for_user(&*cq.curr_compl_x_l());
            if v.len() != n_us {
                return false;
            }
            std::ptr::copy_nonoverlapping(v.as_ptr(), compl_x_l, n_us);
        }
        if !compl_x_u.is_null() && n_us > 0 {
            let v = nlp.pack_z_u_for_user(&*cq.curr_compl_x_u());
            if v.len() != n_us {
                return false;
            }
            std::ptr::copy_nonoverlapping(v.as_ptr(), compl_x_u, n_us);
        }
        if !grad_lag_x.is_null() && n_us > 0 {
            let glx = cq.curr_grad_lag_x();
            // Scatter compressed x-var → full-x via lift_x_to_full
            // (treats `glx` as if it were an x-vector). Fixed-variable
            // slots remain zero.
            let full = nlp.lift_x_to_full(&*glx);
            if full.len() != n_us {
                return false;
            }
            std::ptr::copy_nonoverlapping(full.as_ptr(), grad_lag_x, n_us);
        }
        if !nlp_constraint_violation.is_null() && m_us > 0 {
            // Per-row equality and range violation reconstruction in
            // full-g coordinates is a follow-up. The scalar
            // `curr_primal_infeasibility_max` (== `inf_pr` reported in
            // `IterStats`) is the outer summary; populate per-row
            // detail as a future refinement and zero-fill for now.
            let zero = vec![0.0; m_us];
            std::ptr::copy_nonoverlapping(zero.as_ptr(), nlp_constraint_violation, m_us);
        }
        if !compl_g.is_null() && m_us > 0 {
            // Per-row constraint complementarity (`v_L .* s_L` /
            // `v_U .* s_U` mapped back to full-g) is also a follow-up.
            let zero = vec![0.0; m_us];
            std::ptr::copy_nonoverlapping(zero.as_ptr(), compl_g, m_us);
        }
        true
    });
    if result.unwrap_or(false) {
        TRUE
    } else {
        FALSE
    }
}

/// Port of `IpStdCInterface.cpp:GetIpoptVersion` (Ipopt 3.14.18+).
/// Writes the pounce crate's `major.minor.patch` into the buffers.
/// Any pointer may be NULL to skip that component.
///
/// # Safety
///
/// Each non-NULL pointer must point at a writable `int`.
#[no_mangle]
pub unsafe extern "C" fn GetIpoptVersion(
    major: *mut c_int,
    minor: *mut c_int,
    release: *mut c_int,
) {
    // Read from Cargo at compile time so the symbol always matches the
    // shipped binary. `unwrap_or(0)` keeps the function infallible if a
    // component is missing from the manifest (shouldn't happen in
    // practice — workspace manifest requires SemVer triples).
    let (mj, mn, pt) = parse_pkg_version(env!("CARGO_PKG_VERSION"));
    if !major.is_null() {
        *major = mj;
    }
    if !minor.is_null() {
        *minor = mn;
    }
    if !release.is_null() {
        *release = pt;
    }
}

fn parse_pkg_version(v: &str) -> (c_int, c_int, c_int) {
    let mut it = v.split('.').map(|s| s.parse::<c_int>().unwrap_or(0));
    (
        it.next().unwrap_or(0),
        it.next().unwrap_or(0),
        it.next().unwrap_or(0),
    )
}

// ----------------------------------------------------------------------
// Pounce extensions: post-solve statistics accessors.
//
// Convenience accessors not present in upstream Ipopt's C API. Valid
// only after [`IpoptSolve`] has returned; calling them on a
// never-solved problem yields zero. They expose the same
// `SolveStatistics` data the Rust API surfaces via
// [`IpoptApplication::statistics`].
// ----------------------------------------------------------------------

/// Number of IPM iterations in the most recent solve, or `0` if the
/// problem has not been solved yet.
///
/// # Safety
///
/// `ipopt_problem` must be a valid `IpoptProblem` or NULL.
#[no_mangle]
pub unsafe extern "C" fn GetIpoptIterCount(ipopt_problem: IpoptProblem) -> Index {
    last_stat(ipopt_problem, |s| s.iteration_count).unwrap_or(0)
}

/// Wall-clock solve time in seconds for the most recent solve, or
/// `0.0` if the problem has not been solved yet.
///
/// # Safety
///
/// `ipopt_problem` must be a valid `IpoptProblem` or NULL.
#[no_mangle]
pub unsafe extern "C" fn GetIpoptSolveTime(ipopt_problem: IpoptProblem) -> Number {
    last_stat(ipopt_problem, |s| s.total_wallclock_time_secs).unwrap_or(0.0)
}

/// Final primal infeasibility (max constraint violation) for the most
/// recent solve.
///
/// # Safety
///
/// `ipopt_problem` must be a valid `IpoptProblem` or NULL.
#[no_mangle]
pub unsafe extern "C" fn GetIpoptPrimalInf(ipopt_problem: IpoptProblem) -> Number {
    last_stat(ipopt_problem, |s| s.final_constr_viol).unwrap_or(0.0)
}

/// Final dual infeasibility (max gradient-of-Lagrangian norm) for the
/// most recent solve.
///
/// # Safety
///
/// `ipopt_problem` must be a valid `IpoptProblem` or NULL.
#[no_mangle]
pub unsafe extern "C" fn GetIpoptDualInf(ipopt_problem: IpoptProblem) -> Number {
    last_stat(ipopt_problem, |s| s.final_dual_inf).unwrap_or(0.0)
}

/// Final complementarity error for the most recent solve.
///
/// # Safety
///
/// `ipopt_problem` must be a valid `IpoptProblem` or NULL.
#[no_mangle]
pub unsafe extern "C" fn GetIpoptComplInf(ipopt_problem: IpoptProblem) -> Number {
    last_stat(ipopt_problem, |s| s.final_compl).unwrap_or(0.0)
}

unsafe fn last_stat<T, F>(ipopt_problem: IpoptProblem, f: F) -> Option<T>
where
    F: FnOnce(&SolveStatistics) -> T,
{
    if ipopt_problem.is_null() {
        return None;
    }
    (*ipopt_problem).last_solve.as_ref().map(|ls| f(&ls.stats))
}

// ─────────────────────────────────────────────────────────────
// Pounce extension: SQP working-set warm-start C ABI (§7.2 of
// `docs/research/active-set-sqp-warm-start.md`).
//
// Three new entry points; all backward-compatible additions.
// No existing signature changes — existing cyipopt / JuMP /
// AMPL clients are unaffected.
// ─────────────────────────────────────────────────────────────

fn bound_status_to_int(s: pounce_qp::BoundStatus) -> c_int {
    use pounce_qp::BoundStatus::*;
    match s {
        Inactive => POUNCE_WS_INACTIVE,
        AtLower => POUNCE_WS_AT_LOWER,
        AtUpper => POUNCE_WS_AT_UPPER,
        Fixed => POUNCE_WS_FIXED_OR_EQ,
    }
}

fn int_to_bound_status(v: c_int) -> Option<pounce_qp::BoundStatus> {
    use pounce_qp::BoundStatus::*;
    match v {
        POUNCE_WS_INACTIVE => Some(Inactive),
        POUNCE_WS_AT_LOWER => Some(AtLower),
        POUNCE_WS_AT_UPPER => Some(AtUpper),
        POUNCE_WS_FIXED_OR_EQ => Some(Fixed),
        _ => None,
    }
}

fn cons_status_to_int(s: pounce_qp::ConsStatus) -> c_int {
    use pounce_qp::ConsStatus::*;
    match s {
        Inactive => POUNCE_WS_INACTIVE,
        AtLower => POUNCE_WS_AT_LOWER,
        AtUpper => POUNCE_WS_AT_UPPER,
        Equality => POUNCE_WS_FIXED_OR_EQ,
    }
}

fn int_to_cons_status(v: c_int) -> Option<pounce_qp::ConsStatus> {
    use pounce_qp::ConsStatus::*;
    match v {
        POUNCE_WS_INACTIVE => Some(Inactive),
        POUNCE_WS_AT_LOWER => Some(AtLower),
        POUNCE_WS_AT_UPPER => Some(AtUpper),
        POUNCE_WS_FIXED_OR_EQ => Some(Equality),
        _ => None,
    }
}

/// Retrieve the working set produced by the most recent SQP solve
/// (`algorithm = active-set-sqp`). Buffer sizes are `n` for
/// `bound_status_out` and `m` for `cons_status_out`. Pass `NULL`
/// for either to skip that side.
///
/// Returns `TRUE` (1) on success, `FALSE` (0) if there is no
/// working set to retrieve (e.g. no SQP solve has run, the IPM
/// path was used, or the very first KKT check declared
/// optimality before solving any QP).
///
/// # Safety
///
/// `ipopt_problem` must be a valid `IpoptProblem`. Output
/// buffers (when non-NULL) must be sized at least `n` and `m`
/// respectively.
#[no_mangle]
pub unsafe extern "C" fn IpoptGetWorkingSet(
    ipopt_problem: IpoptProblem,
    bound_status_out: *mut IpoptBoundStatus,
    cons_status_out: *mut IpoptConsStatus,
) -> Bool {
    if ipopt_problem.is_null() {
        return FALSE;
    }
    let info = &*ipopt_problem;
    let ws = match info.app.last_sqp_working_set() {
        Some(w) => w,
        None => return FALSE,
    };
    if !bound_status_out.is_null() {
        for (i, &s) in ws.bounds.iter().enumerate() {
            *bound_status_out.add(i) = bound_status_to_int(s);
        }
    }
    if !cons_status_out.is_null() {
        for (i, &s) in ws.constraints.iter().enumerate() {
            *cons_status_out.add(i) = cons_status_to_int(s);
        }
    }
    TRUE
}

/// Supply a warm-start working set consumed by the next
/// [`IpoptSolve`] on this problem. Pass `NULL` for either side to
/// cold-start it. The caller-owned buffers are copied; reuse
/// across calls is safe.
///
/// Returns `TRUE` on success, `FALSE` on (a) NULL problem, (b)
/// an out-of-range status code in one of the buffers, or
/// (c) both inputs NULL (which would equal a no-op
/// — call [`IpoptClearWarmStartWorkingSet`] instead).
///
/// # Safety
///
/// `ipopt_problem` must be valid. `bound_status_in` (when
/// non-NULL) must be sized `n`; `cons_status_in` (when non-NULL)
/// must be sized `m`.
#[no_mangle]
pub unsafe extern "C" fn IpoptSetWarmStartWorkingSet(
    ipopt_problem: IpoptProblem,
    bound_status_in: *const IpoptBoundStatus,
    cons_status_in: *const IpoptConsStatus,
) -> Bool {
    if ipopt_problem.is_null() {
        return FALSE;
    }
    if bound_status_in.is_null() && cons_status_in.is_null() {
        return FALSE;
    }
    let info = &mut *ipopt_problem;
    let n = info.n.max(0) as usize;
    let m = info.m.max(0) as usize;
    let mut bounds = vec![pounce_qp::BoundStatus::Inactive; n];
    if !bound_status_in.is_null() {
        for i in 0..n {
            let v = *bound_status_in.add(i);
            match int_to_bound_status(v) {
                Some(s) => bounds[i] = s,
                None => return FALSE,
            }
        }
    }
    let mut constraints = vec![pounce_qp::ConsStatus::Inactive; m];
    if !cons_status_in.is_null() {
        for i in 0..m {
            let v = *cons_status_in.add(i);
            match int_to_cons_status(v) {
                Some(s) => constraints[i] = s,
                None => return FALSE,
            }
        }
    }
    // We do *not* know the primal/dual iterate here — the caller
    // either left them at default zeros (cold) or already wrote
    // them into `x` before calling `IpoptSolve`. We seed
    // `SqpIterates` with zeros; `IpoptSolve` will use its `x`
    // argument as the starting point (the SqpProblemSpec adapter
    // wraps `IpoptNlp::get_starting_x`, which the C path
    // initializes from the user-supplied `x` buffer).
    info.app
        .set_sqp_warm_start(pounce_algorithm::sqp::SqpIterates {
            x: vec![0.0; n],
            lambda_g: vec![0.0; m],
            lambda_x: vec![0.0; n],
            working: Some(pounce_qp::WorkingSet {
                bounds,
                constraints,
            }),
        });
    TRUE
}

/// Drop any pending warm-start working set without solving. The
/// next [`IpoptSolve`] will cold-start.
///
/// # Safety
///
/// `ipopt_problem` must be a valid `IpoptProblem` or NULL.
#[no_mangle]
pub unsafe extern "C" fn IpoptClearWarmStartWorkingSet(ipopt_problem: IpoptProblem) -> Bool {
    if ipopt_problem.is_null() {
        return FALSE;
    }
    (*ipopt_problem).app.clear_sqp_warm_start();
    TRUE
}

/// Convenience one-shot: equivalent to
/// `IpoptSetWarmStartWorkingSet` + `IpoptSolve` +
/// `IpoptGetWorkingSet` in sequence. The input/output working-set
/// buffers are independent (so a caller can read back the new
/// working set into the same array used as input). Pass `NULL`
/// for any in/out buffer to skip that side.
///
/// Returns the `ApplicationReturnStatus` integer, identical to
/// [`IpoptSolve`].
///
/// # Safety
///
/// All pointer arguments follow the same contract as
/// `IpoptSolve` plus the working-set buffer sizes documented on
/// `IpoptSetWarmStartWorkingSet` / `IpoptGetWorkingSet`.
#[allow(clippy::too_many_arguments)]
#[no_mangle]
pub unsafe extern "C" fn IpoptSolveWarmStart(
    ipopt_problem: IpoptProblem,
    x: *mut Number,
    g: *mut Number,
    obj_val: *mut Number,
    mult_g: *mut Number,
    mult_x_L: *mut Number,
    mult_x_U: *mut Number,
    bound_status_in: *const IpoptBoundStatus,
    cons_status_in: *const IpoptConsStatus,
    bound_status_out: *mut IpoptBoundStatus,
    cons_status_out: *mut IpoptConsStatus,
    user_data: *mut c_void,
) -> Index {
    if ipopt_problem.is_null() {
        return ApplicationReturnStatus::InternalError as Index;
    }
    // Guard the working-set set/get helpers too. The inner `IpoptSolve` is
    // independently guarded, but a panic in the warm-start working-set
    // marshalling would otherwise still abort across `extern "C"`.
    ffi_guard(ApplicationReturnStatus::InternalError as Index, || unsafe {
        // Best-effort set. Errors here (e.g. bad status code) are
        // silently treated as cold-start; the caller can probe via
        // `IpoptSetWarmStartWorkingSet` directly if they need to
        // validate the input.
        if !bound_status_in.is_null() || !cons_status_in.is_null() {
            let _ = IpoptSetWarmStartWorkingSet(ipopt_problem, bound_status_in, cons_status_in);
        }
        let status = IpoptSolve(
            ipopt_problem,
            x,
            g,
            obj_val,
            mult_g,
            mult_x_L,
            mult_x_U,
            user_data,
        );
        let _ = IpoptGetWorkingSet(ipopt_problem, bound_status_out, cons_status_out);
        status
    })
}

/// Adapter that bridges the user-supplied C callback table to the
/// in-crate [`TNLP`] trait. Mirrors `Interfaces/IpStdInterfaceTNLP.cpp`
/// (`StdInterfaceTNLP`); each TNLP method forwards to the matching
/// `Eval_*_CB` and propagates `false` returns up so the algorithm
/// layer can map them to `Invalid_Number_Detected`.
///
/// Holds a snapshot of bounds and the initial `x`. After `optimize_tnlp`
/// finishes, `finalize_solution` is called by the algorithm layer; the
/// adapter records the final iterate in `final_*` fields, which the
/// outer [`IpoptSolve`] copies back into the caller's buffers.
pub(crate) struct CCallbackTnlp {
    pub(crate) n: Index,
    pub(crate) m: Index,
    pub(crate) nele_jac: Index,
    pub(crate) nele_hess: Index,
    pub(crate) index_style: Index,
    pub(crate) x_l: Vec<Number>,
    pub(crate) x_u: Vec<Number>,
    pub(crate) g_l: Vec<Number>,
    pub(crate) g_u: Vec<Number>,
    pub(crate) initial_x: Vec<Number>,
    pub(crate) eval_f: Option<Eval_F_CB>,
    pub(crate) eval_grad_f: Option<Eval_Grad_F_CB>,
    pub(crate) eval_g: Option<Eval_G_CB>,
    pub(crate) eval_jac_g: Option<Eval_Jac_G_CB>,
    pub(crate) eval_h: Option<Eval_H_CB>,
    pub(crate) user_data: *mut c_void,
    /// User-installed intermediate callback, copied at solve time so the
    /// TNLP-trait `intermediate_callback` impl can forward through to it.
    pub(crate) intermediate_cb: Option<Intermediate_CB>,
    /// Snapshot of user-provided scaling captured at solve time.
    pub(crate) user_scaling: Option<UserScaling>,
    pub(crate) final_status: Option<pounce_nlp::alg_types::SolverReturn>,
    pub(crate) final_x: Vec<Number>,
    pub(crate) final_z_l: Vec<Number>,
    pub(crate) final_z_u: Vec<Number>,
    pub(crate) final_g: Vec<Number>,
    pub(crate) final_lambda: Vec<Number>,
    pub(crate) final_obj: Number,
}

impl TNLP for CCallbackTnlp {
    fn get_nlp_info(&mut self) -> Option<NlpInfo> {
        Some(NlpInfo {
            n: self.n as pounce_common::types::Index,
            m: self.m as pounce_common::types::Index,
            nnz_jac_g: self.nele_jac as pounce_common::types::Index,
            nnz_h_lag: self.nele_hess as pounce_common::types::Index,
            index_style: if self.index_style == 1 {
                IndexStyle::Fortran
            } else {
                IndexStyle::C
            },
        })
    }

    fn get_bounds_info(&mut self, b: BoundsInfo<'_>) -> bool {
        if !self.x_l.is_empty() {
            b.x_l.copy_from_slice(&self.x_l);
        }
        if !self.x_u.is_empty() {
            b.x_u.copy_from_slice(&self.x_u);
        }
        if !self.g_l.is_empty() {
            b.g_l.copy_from_slice(&self.g_l);
        }
        if !self.g_u.is_empty() {
            b.g_u.copy_from_slice(&self.g_u);
        }
        true
    }

    fn get_starting_point(&mut self, sp: StartingPoint<'_>) -> bool {
        if !self.initial_x.is_empty() {
            sp.x.copy_from_slice(&self.initial_x);
        }
        true
    }

    fn get_scaling_parameters(&mut self, req: ScalingRequest<'_>) -> bool {
        let Some(s) = self.user_scaling.as_ref() else {
            return false;
        };
        *req.obj_scaling = s.obj_scaling;
        if let Some(x) = s.x_scaling.as_ref() {
            if x.len() == req.x_scaling.len() {
                req.x_scaling.copy_from_slice(x);
                *req.use_x_scaling = true;
            }
        } else {
            *req.use_x_scaling = false;
        }
        if let Some(g) = s.g_scaling.as_ref() {
            if g.len() == req.g_scaling.len() {
                req.g_scaling.copy_from_slice(g);
                *req.use_g_scaling = true;
            }
        } else {
            *req.use_g_scaling = false;
        }
        true
    }

    fn eval_f(&mut self, x: &[Number], new_x: bool) -> Option<Number> {
        let cb = self.eval_f?;
        let mut obj = 0.0;
        let ok = unsafe {
            cb(
                self.n,
                x.as_ptr() as *mut Number,
                if new_x { TRUE } else { FALSE },
                &mut obj,
                self.user_data,
            )
        };
        if ok != FALSE {
            Some(obj)
        } else {
            None
        }
    }

    fn eval_grad_f(&mut self, x: &[Number], new_x: bool, grad_f: &mut [Number]) -> bool {
        let Some(cb) = self.eval_grad_f else {
            return false;
        };
        let ok = unsafe {
            cb(
                self.n,
                x.as_ptr() as *mut Number,
                if new_x { TRUE } else { FALSE },
                grad_f.as_mut_ptr(),
                self.user_data,
            )
        };
        ok != FALSE
    }

    fn eval_g(&mut self, x: &[Number], new_x: bool, g: &mut [Number]) -> bool {
        if self.m == 0 {
            return true;
        }
        let Some(cb) = self.eval_g else {
            return false;
        };
        let ok = unsafe {
            cb(
                self.n,
                x.as_ptr() as *mut Number,
                if new_x { TRUE } else { FALSE },
                self.m,
                g.as_mut_ptr(),
                self.user_data,
            )
        };
        ok != FALSE
    }

    fn eval_jac_g(&mut self, x: Option<&[Number]>, new_x: bool, mode: SparsityRequest<'_>) -> bool {
        if self.m == 0 || self.nele_jac == 0 {
            return true;
        }
        let Some(cb) = self.eval_jac_g else {
            return false;
        };
        let x_ptr = x
            .map(|s| s.as_ptr() as *mut Number)
            .unwrap_or(std::ptr::null_mut());
        let ok = match mode {
            SparsityRequest::Structure { irow, jcol } => unsafe {
                cb(
                    self.n,
                    x_ptr,
                    if new_x { TRUE } else { FALSE },
                    self.m,
                    self.nele_jac,
                    irow.as_mut_ptr(),
                    jcol.as_mut_ptr(),
                    std::ptr::null_mut(),
                    self.user_data,
                )
            },
            SparsityRequest::Values { values } => unsafe {
                cb(
                    self.n,
                    x_ptr,
                    if new_x { TRUE } else { FALSE },
                    self.m,
                    self.nele_jac,
                    std::ptr::null_mut(),
                    std::ptr::null_mut(),
                    values.as_mut_ptr(),
                    self.user_data,
                )
            },
        };
        ok != FALSE
    }

    fn eval_h(
        &mut self,
        x: Option<&[Number]>,
        new_x: bool,
        obj_factor: Number,
        lambda: Option<&[Number]>,
        new_lambda: bool,
        mode: SparsityRequest<'_>,
    ) -> bool {
        let Some(cb) = self.eval_h else {
            return false;
        };
        if self.nele_hess == 0 {
            return true;
        }
        let x_ptr = x
            .map(|s| s.as_ptr() as *mut Number)
            .unwrap_or(std::ptr::null_mut());
        let lambda_ptr = lambda
            .map(|s| s.as_ptr() as *mut Number)
            .unwrap_or(std::ptr::null_mut());
        let ok = match mode {
            SparsityRequest::Structure { irow, jcol } => unsafe {
                cb(
                    self.n,
                    x_ptr,
                    if new_x { TRUE } else { FALSE },
                    obj_factor,
                    self.m,
                    lambda_ptr,
                    if new_lambda { TRUE } else { FALSE },
                    self.nele_hess,
                    irow.as_mut_ptr(),
                    jcol.as_mut_ptr(),
                    std::ptr::null_mut(),
                    self.user_data,
                )
            },
            SparsityRequest::Values { values } => unsafe {
                cb(
                    self.n,
                    x_ptr,
                    if new_x { TRUE } else { FALSE },
                    obj_factor,
                    self.m,
                    lambda_ptr,
                    if new_lambda { TRUE } else { FALSE },
                    self.nele_hess,
                    std::ptr::null_mut(),
                    std::ptr::null_mut(),
                    values.as_mut_ptr(),
                    self.user_data,
                )
            },
        };
        ok != FALSE
    }

    fn intermediate_callback(
        &mut self,
        stats: pounce_nlp::tnlp::IterStats,
        _ip_data: &IpoptData,
        _ip_cq: &IpoptCq,
    ) -> bool {
        let Some(cb) = self.intermediate_cb else {
            return true;
        };
        let ok = unsafe {
            cb(
                stats.mode as Index,
                stats.iter as Index,
                stats.obj_value,
                stats.inf_pr,
                stats.inf_du,
                stats.mu,
                stats.d_norm,
                stats.regularization_size,
                stats.alpha_du,
                stats.alpha_pr,
                stats.ls_trials as Index,
                self.user_data,
            )
        };
        ok != FALSE
    }

    fn finalize_solution(&mut self, sol: Solution<'_>, _d: &IpoptData, _q: &IpoptCq) {
        self.final_status = Some(sol.status);
        if !sol.x.is_empty() {
            self.final_x.copy_from_slice(sol.x);
        }
        if !sol.z_l.is_empty() {
            self.final_z_l.copy_from_slice(sol.z_l);
        }
        if !sol.z_u.is_empty() {
            self.final_z_u.copy_from_slice(sol.z_u);
        }
        if !sol.g.is_empty() {
            self.final_g.copy_from_slice(sol.g);
        }
        if !sol.lambda.is_empty() {
            self.final_lambda.copy_from_slice(sol.lambda);
        }
        self.final_obj = sol.obj_value;
    }
}

/// Enable per-iteration history capture on the underlying
/// `IpoptApplication`. Must be called *before* [`IpoptSolve`] for the
/// trajectory to appear in the report written by
/// [`IpoptWriteSolveReport`]. Off by default — capturing each iterate
/// has a small per-iter cost the IPM core skips otherwise.
///
/// Returns `TRUE` on success, `FALSE` if `ipopt_problem` is NULL.
///
/// # Safety
///
/// `ipopt_problem` must be a valid handle returned by
/// [`CreateIpoptProblem`] (or `NULL`).
#[no_mangle]
pub unsafe extern "C" fn IpoptEnableIterHistory(ipopt_problem: IpoptProblem) -> Bool {
    if ipopt_problem.is_null() {
        return FALSE;
    }
    let info = unsafe { &mut *ipopt_problem };
    info.app.enable_iter_history();
    TRUE
}

/// Write a `pounce.solve-report/v1` JSON file capturing the most
/// recent [`IpoptSolve`] result. `path` is a NUL-terminated UTF-8
/// filesystem path. `detail` is one of `"summary"` or `"full"`
/// (NUL-terminated); pass `NULL` for the default (`"summary"`).
///
/// When `detail = "full"` and [`IpoptEnableIterHistory`] was called
/// pre-solve, the per-iteration trajectory is embedded so that
/// downstream tools (`diagnose`, `find_stalls`, `convergence_trace`)
/// see the same trace the `pounce` CLI's `--json-output` path
/// produces. The input descriptor is recorded as `tnlp-direct`
/// because the cinterface receives callbacks rather than a file.
///
/// Returns `TRUE` on a successful write, `FALSE` for NULL handle,
/// no prior solve, an invalid `detail`, a bad path, or an I/O error.
///
/// # Safety
///
/// `ipopt_problem` must be a valid handle; `path` must be a valid
/// NUL-terminated UTF-8 string; `detail` must be NULL or a valid
/// NUL-terminated UTF-8 string.
#[no_mangle]
pub unsafe extern "C" fn IpoptWriteSolveReport(
    ipopt_problem: IpoptProblem,
    path: *const c_char,
    detail: *const c_char,
) -> Bool {
    use pounce_solve_report::{
        status_to_solve_result_num, write_report_file, InputDescriptor, ReportBuilder, ReportDetail,
    };

    // Guard the report build/write: it clones the retained iterate and runs
    // the `pounce-solve-report` serializer + file I/O, any of which could
    // panic on an unexpected state. A panic unwinding across `extern "C"`
    // aborts the embedding process; report `FALSE` instead. (See `ffi_guard`.)
    ffi_guard(FALSE, || unsafe {
        if ipopt_problem.is_null() || path.is_null() {
            return FALSE;
        }
        let info = &*ipopt_problem;
        let Some(last) = info.last_solve.as_ref() else {
            return FALSE;
        };

        let Ok(path_str) = CStr::from_ptr(path).to_str() else {
            return FALSE;
        };

        let detail_choice = if detail.is_null() {
            ReportDetail::Summary
        } else {
            let Ok(detail_str) = CStr::from_ptr(detail).to_str() else {
                return FALSE;
            };
            match ReportDetail::parse(detail_str) {
                Ok(d) => d,
                Err(_) => return FALSE,
            }
        };

        let mut builder = ReportBuilder::new(detail_choice, InputDescriptor::TnlpDirect);
        builder.problem.n_variables = info.n;
        builder.problem.n_constraints = info.m;
        builder.problem.n_objectives = 1;
        builder.problem.nnz_jac_g = Some(info.nele_jac);
        builder.problem.nnz_h_lag = Some(info.nele_hess);

        builder.solution.status = last.status;
        builder.solution.solve_result_num = status_to_solve_result_num(last.status);
        builder.solution.objective = last.final_obj;
        builder.solution.x = last.final_x.clone();
        builder.solution.lambda = last.final_lambda.clone();

        builder.ingest_stats(&last.stats);
        if let Some(linsol) = last.linear_solver.clone() {
            builder.set_linear_solver_summary(linsol);
        }

        let report = builder.finish();
        match write_report_file(std::path::Path::new(path_str), &report) {
            Ok(_) => TRUE,
            Err(_) => FALSE,
        }
    })
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::ffi::CString;

    unsafe extern "C" fn dummy_eval_f(
        _n: Index,
        _x: *const Number,
        _new_x: Bool,
        _obj_value: *mut Number,
        _user_data: *mut c_void,
    ) -> Bool {
        TRUE
    }
    unsafe extern "C" fn dummy_eval_grad_f(
        _n: Index,
        _x: *const Number,
        _new_x: Bool,
        _grad_f: *mut Number,
        _user_data: *mut c_void,
    ) -> Bool {
        TRUE
    }

    fn create_unconstrained() -> IpoptProblem {
        let xl = [-1.0; 4];
        let xu = [1.0; 4];
        unsafe {
            CreateIpoptProblem(
                4,
                xl.as_ptr(),
                xu.as_ptr(),
                0,
                std::ptr::null(),
                std::ptr::null(),
                0,
                10,
                0,
                Some(dummy_eval_f),
                None,
                Some(dummy_eval_grad_f),
                None,
                None,
            )
        }
    }

    #[test]
    fn create_succeeds_for_unconstrained_problem() {
        let p = create_unconstrained();
        assert!(!p.is_null());
        unsafe { FreeIpoptProblem(p) };
    }

    #[test]
    fn create_returns_null_on_missing_required_callbacks() {
        let xl = [-1.0; 4];
        let xu = [1.0; 4];
        let p = unsafe {
            CreateIpoptProblem(
                4,
                xl.as_ptr(),
                xu.as_ptr(),
                0,
                std::ptr::null(),
                std::ptr::null(),
                0,
                10,
                0,
                None, // missing eval_f
                None,
                Some(dummy_eval_grad_f),
                None,
                None,
            )
        };
        assert!(p.is_null());
    }

    #[test]
    fn create_returns_null_on_negative_n() {
        let p = unsafe {
            CreateIpoptProblem(
                -1,
                std::ptr::null(),
                std::ptr::null(),
                0,
                std::ptr::null(),
                std::ptr::null(),
                0,
                10,
                0,
                Some(dummy_eval_f),
                None,
                Some(dummy_eval_grad_f),
                None,
                None,
            )
        };
        assert!(p.is_null());
    }

    #[test]
    fn create_returns_null_on_invalid_index_style() {
        let xl = [0.0; 1];
        let xu = [1.0; 1];
        let p = unsafe {
            CreateIpoptProblem(
                1,
                xl.as_ptr(),
                xu.as_ptr(),
                0,
                std::ptr::null(),
                std::ptr::null(),
                0,
                1,
                2, // valid values are 0 and 1
                Some(dummy_eval_f),
                None,
                Some(dummy_eval_grad_f),
                None,
                None,
            )
        };
        assert!(p.is_null());
    }

    #[test]
    fn add_int_option_forwards_to_application() {
        let p = create_unconstrained();
        let key = CString::new("print_level").unwrap();
        let ok = unsafe { AddIpoptIntOption(p, key.as_ptr(), 5) };
        assert_eq!(ok, TRUE);
        let info = unsafe { &*p };
        let (level, found) = info
            .app
            .options()
            .get_integer_value("print_level", "")
            .unwrap();
        assert!(found);
        assert_eq!(level, 5);
        unsafe { FreeIpoptProblem(p) };
    }

    #[test]
    fn add_str_option_with_invalid_key_returns_false() {
        let p = create_unconstrained();
        let key = CString::new("totally_unknown_option").unwrap();
        let val = CString::new("yes").unwrap();
        let ok = unsafe { AddIpoptStrOption(p, key.as_ptr(), val.as_ptr()) };
        assert_eq!(ok, FALSE);
        unsafe { FreeIpoptProblem(p) };
    }

    #[test]
    fn add_options_on_null_problem_returns_false() {
        let key = CString::new("print_level").unwrap();
        let v = CString::new("yes").unwrap();
        unsafe {
            assert_eq!(
                AddIpoptIntOption(std::ptr::null_mut(), key.as_ptr(), 5),
                FALSE
            );
            assert_eq!(
                AddIpoptNumOption(std::ptr::null_mut(), key.as_ptr(), 1.0),
                FALSE
            );
            assert_eq!(
                AddIpoptStrOption(std::ptr::null_mut(), key.as_ptr(), v.as_ptr()),
                FALSE
            );
        }
    }

    unsafe extern "C" fn dummy_intermediate(
        _alg_mod: Index,
        _iter_count: Index,
        _obj_value: Number,
        _inf_pr: Number,
        _inf_du: Number,
        _mu: Number,
        _d_norm: Number,
        _regularization_size: Number,
        _alpha_du: Number,
        _alpha_pr: Number,
        _ls_trials: Index,
        _user_data: *mut c_void,
    ) -> Bool {
        TRUE
    }

    #[test]
    fn set_intermediate_callback_stores_pointer() {
        let p = create_unconstrained();
        let ok = unsafe { SetIntermediateCallback(p, Some(dummy_intermediate)) };
        assert_eq!(ok, TRUE);
        let info = unsafe { &*p };
        assert!(info.intermediate_cb.is_some());
        unsafe { FreeIpoptProblem(p) };
    }

    #[test]
    fn solve_returns_internal_error_on_null_problem() {
        let rc = unsafe {
            IpoptSolve(
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
            )
        };
        assert_eq!(rc, -199);
    }

    #[test]
    fn free_null_is_safe() {
        unsafe { FreeIpoptProblem(std::ptr::null_mut()) };
    }

    // ---- End-to-end bridge: 1-D unconstrained quadratic ----
    //
    // f(x) = (x - 2)^2, no bounds, no constraints. Newton driver
    // converges in one step.

    unsafe extern "C" fn quad_eval_f(
        _n: Index,
        x: *const Number,
        _new_x: Bool,
        obj_value: *mut Number,
        _user_data: *mut c_void,
    ) -> Bool {
        let v = *x.offset(0);
        *obj_value = (v - 2.0) * (v - 2.0);
        TRUE
    }
    unsafe extern "C" fn quad_eval_grad_f(
        _n: Index,
        x: *const Number,
        _new_x: Bool,
        grad: *mut Number,
        _user_data: *mut c_void,
    ) -> Bool {
        let v = *x.offset(0);
        *grad.offset(0) = 2.0 * (v - 2.0);
        TRUE
    }
    unsafe extern "C" fn quad_eval_h(
        _n: Index,
        _x: *const Number,
        _new_x: Bool,
        obj_factor: Number,
        _m: Index,
        _lambda: *const Number,
        _new_lambda: Bool,
        _nele_hess: Index,
        irow: *mut Index,
        jcol: *mut Index,
        values: *mut Number,
        _user_data: *mut c_void,
    ) -> Bool {
        if !irow.is_null() && !jcol.is_null() && values.is_null() {
            *irow.offset(0) = 0;
            *jcol.offset(0) = 0;
        } else if irow.is_null() && jcol.is_null() && !values.is_null() {
            *values.offset(0) = 2.0 * obj_factor;
        } else {
            return FALSE;
        }
        TRUE
    }

    #[test]
    fn solve_drives_unconstrained_quadratic_through_bridge() {
        // Bounds wide open (kappa1 push won't move us off 0.0 since
        // |0| < 1e19, but the Newton step lands us at 2.0 anyway).
        let xl = [-1.0e20];
        let xu = [1.0e20];
        let p = unsafe {
            CreateIpoptProblem(
                1,
                xl.as_ptr(),
                xu.as_ptr(),
                0,
                std::ptr::null(),
                std::ptr::null(),
                0,
                1,
                0,
                Some(quad_eval_f),
                None,
                Some(quad_eval_grad_f),
                None,
                Some(quad_eval_h),
            )
        };
        assert!(!p.is_null());
        let mut x = [0.0_f64];
        let mut obj = 0.0_f64;
        let rc = unsafe {
            IpoptSolve(
                p,
                x.as_mut_ptr(),
                std::ptr::null_mut(),
                &mut obj,
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
            )
        };
        assert_eq!(rc, ApplicationReturnStatus::SolveSucceeded as Index);
        assert!((x[0] - 2.0).abs() < 1e-6, "x[0] = {}", x[0]);
        assert!(obj.abs() < 1e-10, "obj = {}", obj);
        unsafe { FreeIpoptProblem(p) };
    }

    /// F5: `IpoptSolve` invalidates the retained `last_solve` stats **up
    /// front**, so a solve that bails — or whose pounce-internal panic
    /// `ffi_guard` catches (returning `Internal_Error`) — does not leave the
    /// post-solve accessors (`GetIpoptIterCount`, `IpoptWriteSolveReport`, …)
    /// silently reporting the *previous* solve's stats.
    ///
    /// A caught panic can't be injected deterministically through the public
    /// C ABI (a panic in a user `extern "C"` callback aborts at its own
    /// boundary; see `ffi_guard`). We drive the equivalent control-flow shape:
    /// after a successful solve we corrupt `n` to a negative value so the next
    /// `IpoptSolve` returns `InvalidProblemDefinition` from inside the guarded
    /// body **without** reaching the trailing `last_solve = Some(..)` write —
    /// exactly where a caught panic also bails. The up-front clear makes the
    /// accessor report "no data" (0) in both cases rather than stale data.
    #[test]
    fn stale_stats_cleared_when_resolve_bails() {
        let xl = [-1.0e20];
        let xu = [1.0e20];
        let p = unsafe {
            CreateIpoptProblem(
                1,
                xl.as_ptr(),
                xu.as_ptr(),
                0,
                std::ptr::null(),
                std::ptr::null(),
                0,
                1,
                0,
                Some(quad_eval_f),
                None,
                Some(quad_eval_grad_f),
                None,
                Some(quad_eval_h),
            )
        };
        assert!(!p.is_null());

        let mut x = [0.0_f64];
        let mut obj = 0.0_f64;
        let rc = unsafe {
            IpoptSolve(
                p,
                x.as_mut_ptr(),
                std::ptr::null_mut(),
                &mut obj,
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
            )
        };
        assert_eq!(rc, ApplicationReturnStatus::SolveSucceeded as Index);
        // The successful solve recorded real stats.
        let iters_after_success = unsafe { GetIpoptIterCount(p) };
        assert!(
            iters_after_success >= 1,
            "a converged solve should record >=1 iteration, got {iters_after_success}"
        );
        assert!(unsafe { (*p).last_solve.is_some() });

        // Corrupt the problem so the next solve bails early in the guarded body
        // (the same place a caught panic would land) without recording stats.
        unsafe { (*p).n = -1 };
        let mut x2 = [0.0_f64];
        let rc2 = unsafe {
            IpoptSolve(
                p,
                x2.as_mut_ptr(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
            )
        };
        assert_eq!(
            rc2,
            ApplicationReturnStatus::InvalidProblemDefinition as Index
        );

        // Post-fix: the up-front invalidation cleared the retained stats, so
        // the accessor reports "no data" (0), not the previous iteration count.
        // Pre-fix this returned `iters_after_success` (stale).
        assert!(
            unsafe { (*p).last_solve.is_none() },
            "a bailed re-solve must clear stale last_solve (F5)"
        );
        assert_eq!(
            unsafe { GetIpoptIterCount(p) },
            0,
            "stale iteration count must not survive a bailed re-solve (F5)"
        );

        unsafe { FreeIpoptProblem(p) };
    }

    #[test]
    fn solve_invalid_problem_definition_when_x_null() {
        let p = create_unconstrained();
        let rc = unsafe {
            IpoptSolve(
                p,
                std::ptr::null_mut(), // x null but n > 0
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
            )
        };
        assert_eq!(
            rc,
            ApplicationReturnStatus::InvalidProblemDefinition as Index
        );
        unsafe { FreeIpoptProblem(p) };
    }

    // ---- New entry points (issue #19) ----

    #[test]
    fn get_version_writes_pkg_version() {
        let (mut mj, mut mn, mut pt) = (-1, -1, -1);
        unsafe { GetIpoptVersion(&mut mj, &mut mn, &mut pt) };
        let expected = parse_pkg_version(env!("CARGO_PKG_VERSION"));
        assert_eq!((mj, mn, pt), expected);
    }

    #[test]
    fn get_version_tolerates_null_buffers() {
        // None of these should crash.
        unsafe {
            GetIpoptVersion(
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
            )
        };
    }

    #[test]
    fn set_scaling_stores_user_supplied_arrays() {
        let p = create_unconstrained();
        let xs = [2.0, 3.0, 4.0, 5.0];
        let ok = unsafe { SetIpoptProblemScaling(p, 7.0, xs.as_ptr(), std::ptr::null()) };
        assert_eq!(ok, TRUE);
        let info = unsafe { &*p };
        let s = info.user_scaling.as_ref().unwrap();
        assert_eq!(s.obj_scaling, 7.0);
        assert_eq!(s.x_scaling.as_deref(), Some(&xs[..]));
        assert!(s.g_scaling.is_none());
        unsafe { FreeIpoptProblem(p) };
    }

    #[test]
    fn set_scaling_on_null_problem_returns_false() {
        let ok = unsafe {
            SetIpoptProblemScaling(
                std::ptr::null_mut(),
                1.0,
                std::ptr::null(),
                std::ptr::null(),
            )
        };
        assert_eq!(ok, FALSE);
    }

    #[test]
    fn open_output_file_writes_and_attaches_journal() {
        let p = create_unconstrained();
        let dir = std::env::temp_dir().join("pounce-cinterface-test");
        let _ = std::fs::create_dir_all(&dir);
        let path = dir.join("output.log");
        let cstr = CString::new(path.to_string_lossy().as_bytes()).unwrap();
        let ok = unsafe { OpenIpoptOutputFile(p, cstr.as_ptr(), 5) };
        assert_eq!(ok, TRUE);
        // Option should be reflected in the app.
        let info = unsafe { &*p };
        let (level, found) = info
            .app
            .options()
            .get_integer_value("file_print_level", "")
            .unwrap();
        assert!(found);
        assert_eq!(level, 5);
        unsafe { FreeIpoptProblem(p) };
        let _ = std::fs::remove_file(&path);
    }

    #[test]
    fn open_output_file_with_null_inputs_returns_false() {
        let key = CString::new("nope").unwrap();
        unsafe {
            assert_eq!(
                OpenIpoptOutputFile(std::ptr::null_mut(), key.as_ptr(), 0),
                FALSE
            );
        }
        let p = create_unconstrained();
        unsafe {
            assert_eq!(OpenIpoptOutputFile(p, std::ptr::null(), 0), FALSE);
            FreeIpoptProblem(p);
        }
    }

    #[test]
    fn get_current_iterate_returns_false_outside_callback() {
        let p = create_unconstrained();
        let rc = unsafe {
            GetIpoptCurrentIterate(
                p,
                FALSE,
                0,
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                0,
                std::ptr::null_mut(),
                std::ptr::null_mut(),
            )
        };
        assert_eq!(rc, FALSE);
        unsafe { FreeIpoptProblem(p) };
    }

    #[test]
    fn get_current_violations_returns_false_outside_callback() {
        let p = create_unconstrained();
        let rc = unsafe {
            GetIpoptCurrentViolations(
                p,
                FALSE,
                0,
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                0,
                std::ptr::null_mut(),
                std::ptr::null_mut(),
            )
        };
        assert_eq!(rc, FALSE);
        unsafe { FreeIpoptProblem(p) };
    }

    #[test]
    fn post_solve_stats_zero_before_solve() {
        let p = create_unconstrained();
        unsafe {
            assert_eq!(GetIpoptIterCount(p), 0);
            assert_eq!(GetIpoptSolveTime(p), 0.0);
            assert_eq!(GetIpoptPrimalInf(p), 0.0);
            assert_eq!(GetIpoptDualInf(p), 0.0);
            assert_eq!(GetIpoptComplInf(p), 0.0);
            FreeIpoptProblem(p);
        }
    }

    #[test]
    fn post_solve_stats_populated_after_solve() {
        // Reuse the same quadratic as the end-to-end solve test.
        let xl = [-1.0e20];
        let xu = [1.0e20];
        let p = unsafe {
            CreateIpoptProblem(
                1,
                xl.as_ptr(),
                xu.as_ptr(),
                0,
                std::ptr::null(),
                std::ptr::null(),
                0,
                1,
                0,
                Some(quad_eval_f),
                None,
                Some(quad_eval_grad_f),
                None,
                Some(quad_eval_h),
            )
        };
        let mut x = [0.0_f64];
        let mut obj = 0.0_f64;
        let rc = unsafe {
            IpoptSolve(
                p,
                x.as_mut_ptr(),
                std::ptr::null_mut(),
                &mut obj,
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
            )
        };
        assert_eq!(rc, ApplicationReturnStatus::SolveSucceeded as Index);
        // After a successful solve, iter count is recorded (>= 0) and
        // wall time is non-negative; primal/dual/compl norms exist.
        unsafe {
            assert!(GetIpoptIterCount(p) >= 0);
            assert!(GetIpoptSolveTime(p) >= 0.0);
            assert!(GetIpoptPrimalInf(p).is_finite());
            assert!(GetIpoptDualInf(p).is_finite());
            assert!(GetIpoptComplInf(p).is_finite());
            FreeIpoptProblem(p);
        }
    }

    #[test]
    fn write_solve_report_emits_v1_json_with_iter_history() {
        // Quadratic — Newton driver, single iter; just exercises the
        // post-solve report path end-to-end.
        let xl = [-1.0e20];
        let xu = [1.0e20];
        let p = unsafe {
            CreateIpoptProblem(
                1,
                xl.as_ptr(),
                xu.as_ptr(),
                0,
                std::ptr::null(),
                std::ptr::null(),
                0,
                1,
                0,
                Some(quad_eval_f),
                None,
                Some(quad_eval_grad_f),
                None,
                Some(quad_eval_h),
            )
        };

        // Write before any solve must fail.
        let cpath = CString::new("/tmp/pounce_cinterface_no_solve.json").unwrap();
        let bad = unsafe { IpoptWriteSolveReport(p, cpath.as_ptr(), std::ptr::null()) };
        assert_eq!(bad, FALSE);

        // Enable per-iter capture, solve, then write at detail = full.
        assert_eq!(unsafe { IpoptEnableIterHistory(p) }, TRUE);
        let mut x = [0.0_f64];
        let mut obj = 0.0_f64;
        let rc = unsafe {
            IpoptSolve(
                p,
                x.as_mut_ptr(),
                std::ptr::null_mut(),
                &mut obj,
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
            )
        };
        assert_eq!(rc, ApplicationReturnStatus::SolveSucceeded as Index);

        let dir = std::env::temp_dir();
        let path = dir.join("pounce_cinterface_report.json");
        let cpath = CString::new(path.to_str().unwrap()).unwrap();
        let cdetail = CString::new("full").unwrap();
        let ok = unsafe { IpoptWriteSolveReport(p, cpath.as_ptr(), cdetail.as_ptr()) };
        assert_eq!(ok, TRUE);

        // Read it back and check the schema tag + that it parses with
        // the same struct shape pounce-cli uses.
        let txt = std::fs::read_to_string(&path).unwrap();
        assert!(
            txt.contains("\"schema\": \"pounce.solve-report/v1\""),
            "{txt}"
        );
        assert!(txt.contains("\"kind\": \"tnlp-direct\""));
        let parsed: pounce_solve_report::SolveReport = serde_json::from_str(&txt).unwrap();
        assert_eq!(parsed.problem.n_variables, 1);
        assert_eq!(parsed.problem.n_constraints, 0);

        // Invalid detail string is rejected.
        let bad_detail = CString::new("verbose").unwrap();
        let bad = unsafe { IpoptWriteSolveReport(p, cpath.as_ptr(), bad_detail.as_ptr()) };
        assert_eq!(bad, FALSE);

        let _ = std::fs::remove_file(&path);
        unsafe { FreeIpoptProblem(p) };
    }

    // --- Intermediate-callback wiring (issue #19, follow-up) ---
    //
    // The callback only fires on the IPM path (`optimize_constrained`).
    // Unconstrained problems short-circuit through the Newton driver,
    // so these tests use a single-inequality problem to force the IPM.

    unsafe extern "C" fn cb_quad_eval_g(
        _n: Index,
        x: *const Number,
        _new_x: Bool,
        _m: Index,
        g: *mut Number,
        _user_data: *mut c_void,
    ) -> Bool {
        *g.offset(0) = *x.offset(0);
        TRUE
    }
    unsafe extern "C" fn cb_quad_eval_jac_g(
        _n: Index,
        _x: *const Number,
        _new_x: Bool,
        _m: Index,
        nele_jac: Index,
        irow: *mut Index,
        jcol: *mut Index,
        values: *mut Number,
        _user_data: *mut c_void,
    ) -> Bool {
        assert_eq!(nele_jac, 1);
        if !irow.is_null() {
            *irow.offset(0) = 0;
            *jcol.offset(0) = 0;
        }
        if !values.is_null() {
            *values.offset(0) = 1.0;
        }
        TRUE
    }
    unsafe extern "C" fn cb_quad_eval_h(
        _n: Index,
        _x: *const Number,
        _new_x: Bool,
        obj_factor: Number,
        _m: Index,
        _lambda: *const Number,
        _new_lambda: Bool,
        _nele_hess: Index,
        irow: *mut Index,
        jcol: *mut Index,
        values: *mut Number,
        _user_data: *mut c_void,
    ) -> Bool {
        if !irow.is_null() {
            *irow.offset(0) = 0;
            *jcol.offset(0) = 0;
        }
        if !values.is_null() {
            *values.offset(0) = 2.0 * obj_factor;
        }
        TRUE
    }

    fn create_callback_test_problem() -> IpoptProblem {
        // min (x - 2)^2  s.t.  -10 <= x <= 10 (single inequality).
        let xl = [-1.0e20];
        let xu = [1.0e20];
        let gl = [-10.0];
        let gu = [10.0];
        unsafe {
            CreateIpoptProblem(
                1,
                xl.as_ptr(),
                xu.as_ptr(),
                1,
                gl.as_ptr(),
                gu.as_ptr(),
                1,
                1,
                0,
                Some(quad_eval_f),
                Some(cb_quad_eval_g),
                Some(quad_eval_grad_f),
                Some(cb_quad_eval_jac_g),
                Some(cb_quad_eval_h),
            )
        }
    }

    static CB_ITER_COUNTER: std::sync::atomic::AtomicUsize = std::sync::atomic::AtomicUsize::new(0);
    static CB_LAST_ITER: std::sync::atomic::AtomicI32 = std::sync::atomic::AtomicI32::new(-1);
    static CB_INSPECTOR_OK: std::sync::atomic::AtomicBool =
        std::sync::atomic::AtomicBool::new(false);

    unsafe extern "C" fn counting_cb(
        _alg_mod: Index,
        iter_count: Index,
        _obj_value: Number,
        _inf_pr: Number,
        _inf_du: Number,
        _mu: Number,
        _d_norm: Number,
        _regularization_size: Number,
        _alpha_du: Number,
        _alpha_pr: Number,
        _ls_trials: Index,
        user_data: *mut c_void,
    ) -> Bool {
        CB_ITER_COUNTER.fetch_add(1, std::sync::atomic::Ordering::SeqCst);
        CB_LAST_ITER.store(iter_count, std::sync::atomic::Ordering::SeqCst);
        // user_data carries the IpoptProblem so we can exercise the
        // inspector from inside the callback.
        let problem = user_data as IpoptProblem;
        let mut x = [0.0_f64];
        let rc = GetIpoptCurrentIterate(
            problem,
            FALSE,
            1,
            x.as_mut_ptr(),
            std::ptr::null_mut(),
            std::ptr::null_mut(),
            1,
            std::ptr::null_mut(),
            std::ptr::null_mut(),
        );
        if rc == TRUE && x[0].is_finite() {
            CB_INSPECTOR_OK.store(true, std::sync::atomic::Ordering::SeqCst);
        }
        TRUE
    }

    #[test]
    fn intermediate_callback_fires_per_iteration_and_inspector_reads_x() {
        CB_ITER_COUNTER.store(0, std::sync::atomic::Ordering::SeqCst);
        CB_LAST_ITER.store(-1, std::sync::atomic::Ordering::SeqCst);
        CB_INSPECTOR_OK.store(false, std::sync::atomic::Ordering::SeqCst);

        let p = create_callback_test_problem();
        assert!(!p.is_null());
        let ok = unsafe { SetIntermediateCallback(p, Some(counting_cb)) };
        assert_eq!(ok, TRUE);
        let mut x = [0.0_f64];
        let mut obj = 0.0_f64;
        let rc = unsafe {
            IpoptSolve(
                p,
                x.as_mut_ptr(),
                std::ptr::null_mut(),
                &mut obj,
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                p as *mut c_void,
            )
        };
        assert_eq!(rc, ApplicationReturnStatus::SolveSucceeded as Index);
        // At least the iter-0 fire happened, plus one per accepted step.
        let n_fires = CB_ITER_COUNTER.load(std::sync::atomic::Ordering::SeqCst);
        assert!(n_fires >= 2, "callback fired {n_fires} times, want >=2");
        assert!(
            CB_LAST_ITER.load(std::sync::atomic::Ordering::SeqCst) >= 1,
            "last iter should be >= 1 after at least one accepted step"
        );
        assert!(
            CB_INSPECTOR_OK.load(std::sync::atomic::Ordering::SeqCst),
            "GetIpoptCurrentIterate did not return a usable x"
        );
        unsafe { FreeIpoptProblem(p) };
    }

    static CB_VIOL_OK: std::sync::atomic::AtomicBool = std::sync::atomic::AtomicBool::new(false);

    // Bounded variant of `create_callback_test_problem`: x in [0, 10] with a
    // finite lower bound, so the `x_l_violation` / `x_u_violation` branches of
    // GetIpoptCurrentViolations actually scatter a real `x_L`/`x_U` mapping
    // (not the degenerate "no bound" pack).
    fn create_bounded_callback_test_problem() -> IpoptProblem {
        // min (x - 2)^2  s.t.  -10 <= x <= 10,  x in [0, 10].
        let xl = [0.0];
        let xu = [10.0];
        let gl = [-10.0];
        let gu = [10.0];
        unsafe {
            CreateIpoptProblem(
                1,
                xl.as_ptr(),
                xu.as_ptr(),
                1,
                gl.as_ptr(),
                gu.as_ptr(),
                1,
                1,
                0,
                Some(quad_eval_f),
                Some(cb_quad_eval_g),
                Some(quad_eval_grad_f),
                Some(cb_quad_eval_jac_g),
                Some(cb_quad_eval_h),
            )
        }
    }

    unsafe extern "C" fn violations_inspecting_cb(
        _alg_mod: Index,
        _iter_count: Index,
        _obj_value: Number,
        _inf_pr: Number,
        _inf_du: Number,
        _mu: Number,
        _d_norm: Number,
        _regularization_size: Number,
        _alpha_du: Number,
        _alpha_pr: Number,
        _ls_trials: Index,
        user_data: *mut c_void,
    ) -> Bool {
        let problem = user_data as IpoptProblem;
        // Exercise the bound-violation branches (n=1, m=1) from inside an
        // installed intermediate context. Pre-L51 these branches indexed
        // `v[i]` without a length guard; the fix makes them return FALSE on
        // a packed-length mismatch instead of panicking across `extern "C"`.
        let mut x_l_viol = [f64::NAN];
        let mut x_u_viol = [f64::NAN];
        let rc = GetIpoptCurrentViolations(
            problem,
            FALSE,
            1,
            x_l_viol.as_mut_ptr(),
            x_u_viol.as_mut_ptr(),
            std::ptr::null_mut(),
            std::ptr::null_mut(),
            std::ptr::null_mut(),
            1,
            std::ptr::null_mut(),
            std::ptr::null_mut(),
        );
        if rc == TRUE
            && x_l_viol[0].is_finite()
            && x_l_viol[0] >= 0.0
            && x_u_viol[0].is_finite()
            && x_u_viol[0] >= 0.0
        {
            CB_VIOL_OK.store(true, std::sync::atomic::Ordering::SeqCst);
        }
        TRUE
    }

    #[test]
    fn get_current_violations_inside_callback_reports_finite_bounds() {
        CB_VIOL_OK.store(false, std::sync::atomic::Ordering::SeqCst);
        let p = create_bounded_callback_test_problem();
        assert!(!p.is_null());
        let ok = unsafe { SetIntermediateCallback(p, Some(violations_inspecting_cb)) };
        assert_eq!(ok, TRUE);
        let mut x = [5.0_f64];
        let mut obj = 0.0_f64;
        let rc = unsafe {
            IpoptSolve(
                p,
                x.as_mut_ptr(),
                std::ptr::null_mut(),
                &mut obj,
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                p as *mut c_void,
            )
        };
        assert_eq!(rc, ApplicationReturnStatus::SolveSucceeded as Index);
        assert!(
            CB_VIOL_OK.load(std::sync::atomic::Ordering::SeqCst),
            "GetIpoptCurrentViolations did not return finite, non-negative \
             bound violations from inside the callback"
        );
        unsafe { FreeIpoptProblem(p) };
    }

    #[test]
    fn bound_violation_scatter_rejects_oversized_pack_instead_of_panicking() {
        // L51 fail-first (logic level): reproduce the scatter of the
        // `x_l_violation` / `x_u_violation` branches. The packed vector comes
        // from `pack_z_*_for_user`, whose length must equal the output `n`.
        // Pre-fix the branches scattered it with `for (i, s) in
        // packed.enumerate() { v[i] = ... }` over a `vec![0.0; n]` *without*
        // checking the length; an oversized pack indexes `v[i]` out of bounds
        // and panics — and across the real `extern "C"` boundary that panic
        // aborts the embedding process. The fix adds the same length guard
        // the sibling (`compl_*`, `grad_lag_x`) branches already had.
        let n_us = 1usize;
        let packed = vec![0.5_f64, -0.3]; // len 2 != n_us == 1

        // Pre-fix: the unguarded scatter panics on the oversized pack.
        let unguarded = std::panic::catch_unwind(|| {
            let mut v = vec![0.0; n_us];
            for (i, s) in packed.iter().enumerate() {
                v[i] = (-s).max(0.0);
            }
            v
        });
        assert!(
            unguarded.is_err(),
            "unguarded scatter should panic (→ abort across extern \"C\") on an oversized pack"
        );

        // Post-fix: the length guard returns an error instead of panicking.
        let guarded: Result<Vec<f64>, ()> = (|| {
            if packed.len() != n_us {
                return Err(());
            }
            let mut v = vec![0.0; n_us];
            for (i, s) in packed.iter().enumerate() {
                v[i] = (-s).max(0.0);
            }
            Ok(v)
        })();
        assert!(
            guarded.is_err(),
            "guarded scatter should reject the length mismatch (return FALSE), not panic"
        );
    }

    unsafe extern "C" fn user_stop_cb(
        _alg_mod: Index,
        _iter_count: Index,
        _obj_value: Number,
        _inf_pr: Number,
        _inf_du: Number,
        _mu: Number,
        _d_norm: Number,
        _regularization_size: Number,
        _alpha_du: Number,
        _alpha_pr: Number,
        _ls_trials: Index,
        _user_data: *mut c_void,
    ) -> Bool {
        FALSE
    }

    #[test]
    fn intermediate_callback_false_surfaces_user_requested_stop() {
        let p = create_callback_test_problem();
        assert!(!p.is_null());
        let ok = unsafe { SetIntermediateCallback(p, Some(user_stop_cb)) };
        assert_eq!(ok, TRUE);
        let mut x = [0.0_f64];
        let rc = unsafe {
            IpoptSolve(
                p,
                x.as_mut_ptr(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
            )
        };
        assert_eq!(rc, ApplicationReturnStatus::UserRequestedStop as Index);
        unsafe { FreeIpoptProblem(p) };
    }

    #[test]
    fn ffi_guard_converts_panic_to_fallback() {
        // L56: a panic in pounce's own Rust code during a solve must be
        // caught at the FFI boundary and reported as `Internal_Error`, never
        // unwound across `extern "C"` (which aborts the embedding process).
        // This exercises the exact mechanism wrapping IpoptSolve /
        // IpoptSolveWarmStart. (The "boom" panic message printing to stderr
        // is expected — the default panic hook still runs before the catch.)
        let fallback = ApplicationReturnStatus::InternalError as Index;
        let got = ffi_guard(fallback, || -> Index {
            panic!("boom inside solver core");
        });
        assert_eq!(got, fallback);
        assert_eq!(got, ApplicationReturnStatus::InternalError as Index);
    }

    #[test]
    fn ffi_guard_is_transparent_on_success() {
        // On the happy path the guard returns the body's value unchanged, so
        // wrapping IpoptSolve does not alter normal solves (the end-to-end
        // solve tests above confirm this at the public-API level).
        let got = ffi_guard(-99, || 7);
        assert_eq!(got, 7);
    }

    #[test]
    fn parse_pkg_version_handles_missing_components() {
        assert_eq!(parse_pkg_version("1.2.3"), (1, 2, 3));
        assert_eq!(parse_pkg_version("4.5"), (4, 5, 0));
        assert_eq!(parse_pkg_version(""), (0, 0, 0));
        assert_eq!(parse_pkg_version("1.x.3"), (1, 0, 3));
    }

    // ---- Solver-session C ABI (crate::solver) ----

    use crate::solver::{
        IpoptCreateSolver, IpoptFreeSolver, IpoptSolverGetKktDim, IpoptSolverKktSolve,
        IpoptSolverSolve,
    };

    #[test]
    fn solver_create_consumes_problem_handle() {
        let mut p = create_unconstrained();
        assert!(!p.is_null());
        let s = unsafe { IpoptCreateSolver(&mut p) };
        assert!(!s.is_null());
        assert!(
            p.is_null(),
            "IpoptCreateSolver should NULL out the caller's handle"
        );
        unsafe { IpoptFreeSolver(s) };
    }

    #[test]
    fn solver_create_null_inputs_return_null() {
        // NULL pointer-to-handle.
        let s = unsafe { IpoptCreateSolver(std::ptr::null_mut()) };
        assert!(s.is_null());
        // Pointer to a NULL handle.
        let mut p: IpoptProblem = std::ptr::null_mut();
        let s = unsafe { IpoptCreateSolver(&mut p) };
        assert!(s.is_null());
    }

    #[test]
    fn solver_free_null_is_safe() {
        unsafe { IpoptFreeSolver(std::ptr::null_mut()) };
    }

    #[test]
    fn solver_solve_drives_quadratic_and_retains_factor() {
        let xl = [-1.0e20];
        let xu = [1.0e20];
        let mut p = unsafe {
            CreateIpoptProblem(
                1,
                xl.as_ptr(),
                xu.as_ptr(),
                0,
                std::ptr::null(),
                std::ptr::null(),
                0,
                1,
                0,
                Some(quad_eval_f),
                None,
                Some(quad_eval_grad_f),
                None,
                Some(quad_eval_h),
            )
        };
        assert!(!p.is_null());
        let s = unsafe { IpoptCreateSolver(&mut p) };
        assert!(!s.is_null());
        let mut x = [0.0_f64];
        let mut obj = 0.0_f64;
        let rc = unsafe {
            IpoptSolverSolve(
                s,
                x.as_mut_ptr(),
                std::ptr::null_mut(),
                &mut obj,
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
            )
        };
        assert_eq!(rc, ApplicationReturnStatus::SolveSucceeded as Index);
        assert!((x[0] - 2.0).abs() < 1e-6);
        assert!(obj.abs() < 1e-10);

        // After convergence the factor is retained — kkt_dim is positive
        // and a zero RHS back-solves to zero.
        let dim = unsafe { IpoptSolverGetKktDim(s) };
        assert!(dim > 0, "expected positive KKT dim, got {dim}");
        let rhs = vec![0.0_f64; dim as usize];
        let mut lhs = vec![1.0_f64; dim as usize];
        let ok = unsafe { IpoptSolverKktSolve(s, rhs.as_ptr(), lhs.as_mut_ptr()) };
        assert_eq!(ok, TRUE);
        for (i, v) in lhs.iter().enumerate() {
            assert!(v.abs() < 1e-10, "lhs[{i}] = {v} not ~0");
        }
        unsafe { IpoptFreeSolver(s) };
    }

    #[test]
    fn solver_kkt_dim_minus_one_before_solve() {
        let mut p = create_unconstrained();
        let s = unsafe { IpoptCreateSolver(&mut p) };
        assert_eq!(unsafe { IpoptSolverGetKktDim(s) }, -1);
        unsafe { IpoptFreeSolver(s) };
    }

    // ─────────────────────────────────────────────────────────
    // §7.2 SQP working-set warm-start C ABI tests.
    // ─────────────────────────────────────────────────────────

    #[test]
    fn c_get_working_set_returns_false_before_any_solve() {
        let p = create_unconstrained();
        let mut bound_buf = [0; 4];
        let rc = unsafe { IpoptGetWorkingSet(p, bound_buf.as_mut_ptr(), std::ptr::null_mut()) };
        assert_eq!(rc, FALSE);
        unsafe { FreeIpoptProblem(p) };
    }

    #[test]
    fn c_set_warm_start_with_both_null_returns_false() {
        let p = create_unconstrained();
        let rc = unsafe { IpoptSetWarmStartWorkingSet(p, std::ptr::null(), std::ptr::null()) };
        assert_eq!(rc, FALSE);
        unsafe { FreeIpoptProblem(p) };
    }

    #[test]
    fn c_set_warm_start_with_bad_status_code_returns_false() {
        let p = create_unconstrained();
        // Length n = 4; '7' is out of range (valid: 0..=3).
        let bogus = [
            POUNCE_WS_INACTIVE,
            7,
            POUNCE_WS_AT_LOWER,
            POUNCE_WS_INACTIVE,
        ];
        let rc = unsafe { IpoptSetWarmStartWorkingSet(p, bogus.as_ptr(), std::ptr::null()) };
        assert_eq!(rc, FALSE);
        unsafe { FreeIpoptProblem(p) };
    }

    #[test]
    fn c_set_warm_start_then_clear_succeeds() {
        let p = create_unconstrained();
        let in_buf = [POUNCE_WS_INACTIVE; 4];
        let set_rc = unsafe { IpoptSetWarmStartWorkingSet(p, in_buf.as_ptr(), std::ptr::null()) };
        assert_eq!(set_rc, TRUE);
        let clr_rc = unsafe { IpoptClearWarmStartWorkingSet(p) };
        assert_eq!(clr_rc, TRUE);
        unsafe { FreeIpoptProblem(p) };
    }

    #[test]
    fn c_set_warm_start_on_null_problem_returns_false() {
        let in_buf = [POUNCE_WS_INACTIVE; 1];
        let rc = unsafe {
            IpoptSetWarmStartWorkingSet(std::ptr::null_mut(), in_buf.as_ptr(), std::ptr::null())
        };
        assert_eq!(rc, FALSE);
    }

    #[test]
    fn c_solve_warm_start_round_trips_working_set_on_sqp_path() {
        // Use the 1-D `(x − 2)²` quadratic from
        // `create_callback_test_problem`. Set `algorithm
        // active-set-sqp`, solve, then read the working set
        // through `IpoptGetWorkingSet`. Pass it back via
        // `IpoptSolveWarmStart` for a second solve.
        let p = create_callback_test_problem();
        let key = CString::new("algorithm").unwrap();
        let val = CString::new("active-set-sqp").unwrap();
        let ok = unsafe { AddIpoptStrOption(p, key.as_ptr(), val.as_ptr()) };
        assert_eq!(ok, TRUE);

        let mut x = [0.0_f64];
        let mut obj = 0.0_f64;
        let rc1 = unsafe {
            IpoptSolve(
                p,
                x.as_mut_ptr(),
                std::ptr::null_mut(),
                &mut obj,
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
            )
        };
        assert_eq!(rc1, ApplicationReturnStatus::SolveSucceeded as Index);

        let mut bound_buf = [-1; 1];
        let mut cons_buf = [-1; 1];
        let got = unsafe { IpoptGetWorkingSet(p, bound_buf.as_mut_ptr(), cons_buf.as_mut_ptr()) };
        assert_eq!(got, TRUE);
        // Status codes must be in 0..=3.
        assert!((0..=3).contains(&bound_buf[0]));
        assert!((0..=3).contains(&cons_buf[0]));

        // Second solve with the just-retrieved working set as
        // input. Resets x to a non-optimal starting point so the
        // SQP loop actually has work to do; the warm-start
        // should still converge to the optimum.
        x[0] = 0.0;
        let mut obj2 = 0.0_f64;
        let mut bound_out = [-1; 1];
        let mut cons_out = [-1; 1];
        let rc2 = unsafe {
            IpoptSolveWarmStart(
                p,
                x.as_mut_ptr(),
                std::ptr::null_mut(),
                &mut obj2,
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                std::ptr::null_mut(),
                bound_buf.as_ptr(),
                cons_buf.as_ptr(),
                bound_out.as_mut_ptr(),
                cons_out.as_mut_ptr(),
                std::ptr::null_mut(),
            )
        };
        assert_eq!(rc2, ApplicationReturnStatus::SolveSucceeded as Index);
        assert!((0..=3).contains(&bound_out[0]));
        assert!((0..=3).contains(&cons_out[0]));

        unsafe { FreeIpoptProblem(p) };
    }
}