shape-vm 0.3.2

//! Closure (function expression) compilation

use crate::bytecode::{Function, Instruction, OpCode, Operand};
use crate::compiler::monomorphization::type_resolution::concrete_type_for_expr;
use crate::type_tracking::{BindingOwnershipClass, BindingStorageClass};
use shape_ast::ast::type_path::TypePath;
use shape_ast::ast::{Expr, FunctionDef, Span, TypeAnnotation};
use shape_ast::error::{Result, ShapeError};
use shape_runtime::closure::EnvironmentAnalyzer;
use shape_value::v2::concrete_type::{ClosureTypeId, ConcreteType};
use std::collections::BTreeSet;

use super::super::BytecodeCompiler;

/// Strict-typing-sweep (Cluster 2): scan a closure body for binary ops
/// of the form `<param_name> <op> <literal>` (or the symmetric form), and
/// derive a `TypeAnnotation` for `param_name` from the literal's type when
/// the literal has one. This handles the canonical
/// `|x| x + 1` / `|y| y + N` patterns that previously rode on the
/// (now-deleted) Dynamic-emission shim.
///
/// Conservative: returns `None` if the param appears only in untyped
/// contexts, or if the binary op pairs the param with another unknown
/// (e.g. `|x, y| x + y`). The closure body still compiles in those cases
/// — strict-typing simply errors at the offending binary op as before.
pub(crate) fn infer_param_type_from_body(
    param_name: &str,
    body: &[shape_ast::ast::Statement],
) -> Option<TypeAnnotation> {
    use shape_ast::ast::{Literal, Statement};
    fn literal_to_type_ann(lit: &Literal) -> Option<TypeAnnotation> {
        Some(match lit {
            Literal::Int(_) => TypeAnnotation::Basic("int".to_string()),
            Literal::Number(_) => TypeAnnotation::Basic("number".to_string()),
            Literal::Bool(_) => TypeAnnotation::Basic("bool".to_string()),
            Literal::String(_) => TypeAnnotation::Basic("string".to_string()),
            _ => return None,
        })
    }
    fn scan_expr(name: &str, expr: &Expr) -> Option<TypeAnnotation> {
        match expr {
            Expr::BinaryOp { left, right, .. } => {
                if let (Expr::Identifier(n, _), Expr::Literal(lit, _)) =
                    (left.as_ref(), right.as_ref())
                {
                    if n == name {
                        if let Some(t) = literal_to_type_ann(lit) {
                            return Some(t);
                        }
                    }
                }
                if let (Expr::Literal(lit, _), Expr::Identifier(n, _)) =
                    (left.as_ref(), right.as_ref())
                {
                    if n == name {
                        if let Some(t) = literal_to_type_ann(lit) {
                            return Some(t);
                        }
                    }
                }
                scan_expr(name, left).or_else(|| scan_expr(name, right))
            }
            Expr::UnaryOp { operand, .. } => scan_expr(name, operand),
            Expr::FunctionCall { args, .. } => {
                args.iter().find_map(|a| scan_expr(name, a))
            }
            Expr::MethodCall { receiver, args, .. } => {
                scan_expr(name, receiver).or_else(|| args.iter().find_map(|a| scan_expr(name, a)))
            }
            Expr::Array(elements, _) => elements.iter().find_map(|e| scan_expr(name, e)),
            Expr::Return(Some(e), _) => scan_expr(name, e),
            // Match: when the scrutinee is the bare `name`, look at any
            // arm-pattern binding of an identifier and propagate its
            // body/guard usage back to `name`'s type. Conservatively
            // handles the common idiom `match v { x where x > 0 => x }`
            // where `v` and `x` are aliased through pattern binding.
            Expr::Match(match_expr, _) => {
                if let Expr::Identifier(scrutinee_name, _) = match_expr.scrutinee.as_ref() {
                    if scrutinee_name == name {
                        // Look at each arm; if its pattern is a single
                        // identifier `x`, scan the guard + body for
                        // `<x> op <literal>` pairings.
                        for arm in &match_expr.arms {
                            if let shape_ast::ast::Pattern::Identifier(bound_name) =
                                &arm.pattern
                            {
                                if let Some(guard) = arm.guard.as_ref() {
                                    if let Some(t) = scan_expr(bound_name, guard) {
                                        return Some(t);
                                    }
                                }
                                if let Some(t) = scan_expr(bound_name, &arm.body) {
                                    return Some(t);
                                }
                            }
                        }
                    }
                }
                // Otherwise just recurse into scrutinee + arms looking
                // for the original name.
                scan_expr(name, &match_expr.scrutinee)
                    .or_else(|| {
                        match_expr.arms.iter().find_map(|arm| {
                            arm.guard
                                .as_ref()
                                .and_then(|g| scan_expr(name, g))
                                .or_else(|| scan_expr(name, &arm.body))
                        })
                    })
            }
            _ => None,
        }
    }
    fn scan_stmt(name: &str, stmt: &Statement) -> Option<TypeAnnotation> {
        match stmt {
            Statement::Expression(expr, _) => scan_expr(name, expr),
            Statement::Return(Some(e), _) => scan_expr(name, e),
            Statement::VariableDecl(decl, _) => {
                decl.value.as_ref().and_then(|e| scan_expr(name, e))
            }
            Statement::Assignment(asgn, _) => scan_expr(name, &asgn.value),
            _ => None,
        }
    }
    body.iter().find_map(|s| scan_stmt(param_name, s))
}

/// Sweep phase 3c.x: scan a closure body for `param_name op outer_ident`
/// where `outer_ident` has a known type in `known_outer_types`, and
/// propagate that type back to `param_name`. Returns the propagated type
/// name as a `String` (e.g. "int") or `None` if no such pairing is found.
fn infer_param_type_from_outer_pairing(
    param_name: &str,
    body: &[shape_ast::ast::Statement],
    known_outer_types: &std::collections::HashMap<String, String>,
) -> Option<String> {
    use shape_ast::ast::Statement;
    fn scan(name: &str, expr: &Expr, known: &std::collections::HashMap<String, String>) -> Option<String> {
        match expr {
            Expr::BinaryOp { left, right, .. } => {
                if let (Expr::Identifier(ln, _), Expr::Identifier(rn, _)) =
                    (left.as_ref(), right.as_ref())
                {
                    if ln == name {
                        if let Some(t) = known.get(rn) {
                            return Some(t.clone());
                        }
                    }
                    if rn == name {
                        if let Some(t) = known.get(ln) {
                            return Some(t.clone());
                        }
                    }
                }
                scan(name, left, known).or_else(|| scan(name, right, known))
            }
            Expr::UnaryOp { operand, .. } => scan(name, operand, known),
            Expr::Return(Some(e), _) => scan(name, e, known),
            Expr::FunctionCall { args, .. } => {
                args.iter().find_map(|a| scan(name, a, known))
            }
            Expr::MethodCall { receiver, args, .. } => {
                scan(name, receiver, known)
                    .or_else(|| args.iter().find_map(|a| scan(name, a, known)))
            }
            _ => None,
        }
    }
    fn scan_stmt(
        name: &str,
        stmt: &Statement,
        known: &std::collections::HashMap<String, String>,
    ) -> Option<String> {
        match stmt {
            Statement::Expression(e, _) => scan(name, e, known),
            Statement::Return(Some(e), _) => scan(name, e, known),
            _ => None,
        }
    }
    body.iter().find_map(|s| scan_stmt(param_name, s, known_outer_types))
}

/// Strict-typing-sweep (Cluster 1): convert a `ConcreteType` (the v2 typed
/// value-representation type) back into an AST `TypeAnnotation` so it can be
/// attached to a synthetic capture parameter. Returning `None` falls back to
/// the no-annotation path (which is fine for opaque types — those captures
/// never participate in typed binary-ops anyway).
///
/// We map the type-name primitives that `tracked_type_name_from_annotation`
/// recognizes plus `Vec<T>` for arrays. Composite/opaque types
/// (Struct/Enum/Closure/Function/Pointer/HashMap with non-trivial inner)
/// return `None` — they don't need typed-op support inside the closure body.
pub(crate) fn concrete_type_to_type_annotation(ct: &ConcreteType) -> Option<TypeAnnotation> {
    match ct {
        ConcreteType::F64 => Some(TypeAnnotation::Basic("number".to_string())),
        ConcreteType::I64 => Some(TypeAnnotation::Basic("int".to_string())),
        ConcreteType::I32 => Some(TypeAnnotation::Basic("i32".to_string())),
        ConcreteType::I16 => Some(TypeAnnotation::Basic("i16".to_string())),
        ConcreteType::I8 => Some(TypeAnnotation::Basic("i8".to_string())),
        ConcreteType::U64 => Some(TypeAnnotation::Basic("u64".to_string())),
        ConcreteType::U32 => Some(TypeAnnotation::Basic("u32".to_string())),
        ConcreteType::U16 => Some(TypeAnnotation::Basic("u16".to_string())),
        ConcreteType::U8 => Some(TypeAnnotation::Basic("u8".to_string())),
        ConcreteType::Bool => Some(TypeAnnotation::Basic("bool".to_string())),
        ConcreteType::String => Some(TypeAnnotation::Basic("string".to_string())),
        ConcreteType::Decimal => Some(TypeAnnotation::Basic("decimal".to_string())),
        ConcreteType::BigInt => Some(TypeAnnotation::Basic("bigint".to_string())),
        ConcreteType::DateTime => Some(TypeAnnotation::Basic("DateTime".to_string())),
        ConcreteType::Array(inner) => {
            // Render as Vec<T> via the Generic form so
            // `tracked_type_name_from_annotation` produces "Vec<int>" /
            // "Vec<number>" — the names the type-tracker keys typed array
            // ops on.
            concrete_type_to_type_annotation(inner).map(|inner_ann| TypeAnnotation::Generic {
                name: TypePath::simple("Vec"),
                args: vec![inner_ann],
            })
        }
        // Nullable: drop the wrapper — the captured variable is the inner
        // value at the binary-op site if the closure narrows it. No-annotation
        // is safer than a wrong annotation.
        ConcreteType::Option(_) => None,
        // Other composite / opaque types: no useful annotation for the
        // type-tracker. The capture lives as a Pointer-typed slot via the
        // closure layout and does not participate in typed binops.
        _ => None,
    }
}

/// Sweep phase 3c.1: extract a primitive scalar type-name from a
/// runtime `Type`. Mirrors the subset of `numeric_ops::type_display_name`
/// the closure return-type inference cares about.
pub(crate) fn type_display_name_for_closure_inference(
    ty: &shape_runtime::type_system::Type,
) -> String {
    use shape_runtime::type_system::Type;
    match ty {
        Type::Concrete(TypeAnnotation::Basic(name)) => name.clone(),
        Type::Concrete(TypeAnnotation::Reference(name)) => name.to_string(),
        _ => String::new(),
    }
}

/// Sweep phase 3c.1: infer a return-type name for a closure expression
/// based on its body, params, and the outer scope (via `compiler`).
///
/// Conservative; returns `None` when any operand or sub-expression cannot
/// be statically resolved. Used by `update_callable_binding_from_expr` to
/// populate `local_callable_return_types` so a `FunctionCall` against a
/// `let f = |…|` binding can recover `f`'s return type for strict-typing
/// binop dispatch (`f(5) + f(7)` etc.).
///
/// The helper:
/// 1. Honours an explicit `-> T` return annotation when present.
/// 2. Otherwise builds a `HashMap<String, String>` of param-name → tracked
///    type-name from the closure's params (using their annotations or the
///    body-level literal-pairing heuristic the closure compiler itself
///    relies on).
/// 3. Walks the body's terminal expression and resolves identifiers via
///    that map first, then falls back to outer-scope resolution via
///    `concrete_type_for_expr` (which recognises `let base = 100` as I64).
/// 4. Recurses into binary ops, requiring both operand types to agree
///    (and to be one of the primitive scalar names) for the result to be
///    inferred.
pub(crate) fn infer_closure_body_return_type_name(
    compiler: &mut BytecodeCompiler,
    params: &[shape_ast::ast::FunctionParameter],
    body: &[shape_ast::ast::Statement],
    explicit_return: Option<&TypeAnnotation>,
) -> Option<String> {
    infer_closure_body_return_type_name_with_outer(compiler, params, body, explicit_return, &[])
}

/// Sweep phase 3c.x: variant that also accepts a list of enclosing-scope
/// parameters whose names should resolve to their declared types when
/// scanning the closure body. Used by `update_callable_binding_from_expr`
/// for the `let f = make(...)` → `f(arg) + f(arg)` pattern, where `make`'s
/// returned closure captures `make`'s parameters by name and we want to
/// recover their declared types without actually compiling `make`'s body.
pub(crate) fn infer_closure_body_return_type_name_with_outer(
    compiler: &mut BytecodeCompiler,
    params: &[shape_ast::ast::FunctionParameter],
    body: &[shape_ast::ast::Statement],
    explicit_return: Option<&TypeAnnotation>,
    enclosing_params: &[shape_ast::ast::FunctionParameter],
) -> Option<String> {
    infer_closure_body_return_type_name_with_caller_context(
        compiler,
        params,
        body,
        explicit_return,
        enclosing_params,
        &[],
    )
}

/// cluster-2-cw-IB-class-b (2026-05-16, supervisor R3 binding-ratified):
/// caller-context-aware variant of the closure-body return-type inference.
///
/// `caller_arg_type_names[i]` is the type name (e.g. `"Vec<int>"`,
/// `"int"`, `"string"`) of the i-th argument the closure is being called
/// with at the call site. This seeds `param_types[params[i].name]` when
/// the closure param has no explicit annotation AND no body-literal
/// pairing — i.e. the case where the closure's param is inferred-typed
/// at the call site rather than declared.
///
/// Class B fixture (inventory §B.2):
///   `let xs: Array<int> = [1,2,3,4,5]`
///   `let f = |inner| inner.sum()`
///   `print(f(xs))`
///
/// At `f(xs)`, `caller_arg_type_names[0] = Some("Vec<int>")` (derived
/// from `concrete_type_for_expr(xs)` → `Array(I64)` →
/// `concrete_type_to_type_annotation` → `Generic("Vec", [int])` →
/// `tracked_type_name_from_annotation` → `"Vec<int>"`). The body's
/// terminal expression `inner.sum()` then resolves via the extended
/// `expr_type` MethodCall arm: receiver `inner` has type
/// `"Vec<int>"`; method `sum` on `Vec<scalar>` returns the element
/// scalar `"int"`.
///
/// ADR-006 §2.7.5 stamp-at-compile-time: the caller-supplied arg type
/// IS the proof of the closure param's type at the call site — no
/// runtime probe, no fabricated Bool-default. The inference returns
/// `None` when the body's terminal expression cannot be resolved
/// against the seeded param_types.
pub(crate) fn infer_closure_body_return_type_name_with_caller_context(
    compiler: &mut BytecodeCompiler,
    params: &[shape_ast::ast::FunctionParameter],
    body: &[shape_ast::ast::Statement],
    explicit_return: Option<&TypeAnnotation>,
    enclosing_params: &[shape_ast::ast::FunctionParameter],
    caller_arg_type_names: &[Option<String>],
) -> Option<String> {
    use shape_ast::ast::{BinaryOp as Op, Literal, Statement};
    use std::collections::HashMap;

    if let Some(ann) = explicit_return {
        if let Some(name) = BytecodeCompiler::tracked_type_name_from_annotation(ann) {
            return Some(name);
        }
    }

    // Build param-type map. Start with the enclosing-scope params (e.g.
    // the captured `n: int` from `fn make(n: int) -> any { return |x| x + n }`)
    // so the closure body can resolve free identifiers that came from the
    // outer function. Closure-local params override on name collision.
    let mut param_types: HashMap<String, String> = HashMap::new();
    for p in enclosing_params {
        let Some(ident) = p.pattern.as_identifier() else {
            continue;
        };
        if let Some(ann) = &p.type_annotation {
            if let Some(tn) = BytecodeCompiler::tracked_type_name_from_annotation(ann) {
                param_types.insert(ident.to_string(), tn);
            }
        }
    }
    for (param_idx, p) in params.iter().enumerate() {
        let Some(ident) = p.pattern.as_identifier() else {
            continue;
        };
        if let Some(ann) = &p.type_annotation {
            if let Some(tn) = BytecodeCompiler::tracked_type_name_from_annotation(ann) {
                param_types.insert(ident.to_string(), tn);
                continue;
            }
        }
        // Fallback: same body-literal-pairing heuristic the closure
        // compiler uses for unannotated params (`|x| x + 1`).
        if let Some(ann) = infer_param_type_from_body(ident, body) {
            if let Some(tn) = BytecodeCompiler::tracked_type_name_from_annotation(&ann) {
                param_types.insert(ident.to_string(), tn);
            }
        }
        // Sweep phase 3c.x: when the param has no annotation and no
        // body-literal pairing, but the body uses it in a binary op
        // against an enclosing-param that IS typed, infer the closure
        // param's type from the enclosing param's type. Covers
        // `|x| x + n` over `fn make(n: int) ...`.
        if !param_types.contains_key(ident) {
            if let Some(tn) = infer_param_type_from_outer_pairing(ident, body, &param_types) {
                param_types.insert(ident.to_string(), tn);
            }
        }
        // cluster-2-cw-IB-class-b: when no inferred type from local
        // sources, fall through to the caller-context-supplied arg
        // type. The arg's type at the call site IS the proof of the
        // param's type when the closure is invoked there. ADR-006
        // §2.7.5 stamp-at-compile-time — call-site arg type comes
        // from `concrete_type_for_expr(arg)` at bytecode-emission, not
        // from a runtime probe.
        if !param_types.contains_key(ident) {
            if let Some(Some(caller_tn)) = caller_arg_type_names.get(param_idx) {
                param_types.insert(ident.to_string(), caller_tn.clone());
            }
        }
    }

    fn lit_type(lit: &Literal) -> Option<String> {
        Some(
            match lit {
                Literal::Int(_) => "int",
                Literal::Number(_) => "number",
                Literal::Bool(_) => "bool",
                Literal::String(_) | Literal::FormattedString { .. } => "string",
                Literal::Decimal(_) => "decimal",
                _ => return None,
            }
            .to_string(),
        )
    }

    fn expr_type(
        compiler: &mut BytecodeCompiler,
        param_types: &HashMap<String, String>,
        expr: &Expr,
    ) -> Option<String> {
        match expr {
            Expr::Literal(lit, _) => lit_type(lit),
            Expr::Identifier(name, _) => {
                if let Some(tn) = param_types.get(name) {
                    return Some(tn.clone());
                }
                // Outer-scope resolution: try `concrete_type_for_expr`
                // first (covers tracker-recorded primitives + array
                // element types), then fall back to the compiler's
                // `infer_expr_type` (which consults the type-inference
                // engine that ran on the program AST and can see
                // `let base = 100` even when the type tracker has no
                // entry for `base`).
                let ident_expr = Expr::Identifier(name.clone(), Span::DUMMY);
                if let Some(ct) = concrete_type_for_expr(compiler, &ident_expr) {
                    if let Some(tn) = concrete_type_to_type_annotation(&ct)
                        .and_then(|ann| BytecodeCompiler::tracked_type_name_from_annotation(&ann))
                    {
                        return Some(tn);
                    }
                }
                if let Ok(ty) = compiler.infer_expr_type(&ident_expr) {
                    let display = type_display_name_for_closure_inference(&ty);
                    if BytecodeCompiler::tracker_type_name_is_primitive(&display) {
                        return Some(display);
                    }
                }
                None
            }
            Expr::BinaryOp { left, right, op, .. } => {
                let lt = expr_type(compiler, param_types, left)?;
                let rt = expr_type(compiler, param_types, right)?;
                match op {
                    // Arithmetic on matching primitive scalar types
                    // preserves the type. Comparison/logical ops yield
                    // bool.
                    Op::Add | Op::Sub | Op::Mul | Op::Div | Op::Mod => {
                        if lt == rt && BytecodeCompiler::tracker_type_name_is_primitive(&lt) {
                            Some(lt)
                        } else {
                            None
                        }
                    }
                    Op::Equal
                    | Op::NotEqual
                    | Op::Less
                    | Op::LessEq
                    | Op::Greater
                    | Op::GreaterEq
                    | Op::And
                    | Op::Or => Some("bool".to_string()),
                    _ => None,
                }
            }
            Expr::UnaryOp { operand, .. } => expr_type(compiler, param_types, operand),
            Expr::Return(Some(inner), _) => expr_type(compiler, param_types, inner),
            Expr::Block(block, _) => {
                let last = block.items.last()?;
                match last {
                    shape_ast::ast::BlockItem::Expression(e) => {
                        expr_type(compiler, param_types, e)
                    }
                    shape_ast::ast::BlockItem::Statement(s) => {
                        stmt_type(compiler, param_types, s)
                    }
                    _ => None,
                }
            }
            // cluster-2-cw-IB-class-b (2026-05-16, supervisor R3 binding-
            // ratified): MethodCall arm. Mirrors the JIT-side
            // `well_known_method_return_kind` +
            // `parametric_method_return_kind_from_receiver` classifier shape
            // (`crates/shape-jit/src/mir_compiler/types.rs:818-1019`) — the
            // single source of truth for kind-classification across both
            // bytecode-emission and JIT-MIR layers.
            //
            // Class B fixture (inventory §B.2): `let f = |inner| inner.sum()`
            // with `inner` resolved (via caller-context arg type) to
            // `"Vec<int>"`. `inner.sum()` matches the parametric
            // `("sum"|..., Array(elem))` arm and returns the element
            // scalar `"int"`. The downstream conduit value-call
            // destination-stamping pass then stamps the Call-terminator's
            // destination slot with `ConcreteType::I64`, and the JIT-MIR
            // `slot_kinds` projection picks up `NativeKind::Int64`, closing
            // the `print(f(xs))` chain.
            //
            // Invariant-return methods (size/len/length/count → int,
            // isEmpty/contains/has → bool) are receiver-shape-agnostic
            // and matched first. Parametric methods consult the
            // receiver's resolved type name — supports `Vec<scalar>`
            // shape recognition (i.e. element-typed accessors on typed
            // arrays).
            //
            // No tag-bit decode, no Bool-default fallback, no fabricated
            // default — when the receiver type isn't recognised or the
            // method name isn't in either classifier, returns `None` so
            // the outer caller's value-call stamping stays Void per
            // §2.7.5.1 / §2.7.7 #9.
            Expr::MethodCall { receiver, method, args, .. } => {
                // Invariant-across-receiver methods: classify from name
                // alone without needing the receiver's type.
                let invariant_kind: Option<&'static str> = match method.as_str() {
                    "size" | "len" | "length" | "count" => Some("int"),
                    "isEmpty" | "is_empty" | "has" | "contains" => Some("bool"),
                    _ => None,
                };
                if let Some(kind) = invariant_kind {
                    return Some(kind.to_string());
                }

                // Parametric methods: receiver's resolved type name
                // determines the return type. Resolve the receiver via
                // the same expr_type walker (so `inner` resolves to its
                // seeded param_types entry like "Vec<int>").
                let recv_ty = expr_type(compiler, param_types, receiver)?;

                // `Vec<T>` element-typed accessors. The element name
                // strips the `Vec<...>` wrapper. Matches the JIT-side
                // `("sum" | "mean" | "min" | "max", ConcreteType::Array
                // (elem))` arm at `types.rs:976-981`.
                if let Some(elem) = recv_ty
                    .strip_prefix("Vec<")
                    .and_then(|s| s.strip_suffix('>'))
                {
                    match method.as_str() {
                        "sum" | "mean" | "min" | "max" | "get" => {
                            // .get(i) returns element T directly per the
                            // JIT-side classifier; .sum/.mean/.min/.max
                            // also return element T (the typed-array
                            // method registry returns
                            // `KindedSlot::from_<elem>` per receiver-
                            // element kind).
                            if BytecodeCompiler::tracker_type_name_is_primitive(elem) {
                                return Some(elem.to_string());
                            }
                        }
                        _ => {}
                    }
                }

                // Receiver-type-specific arms for built-in scalar types
                // can be added here as needed; bounded to the same set
                // the JIT-side classifier supports to avoid drift.
                let _ = args;
                None
            }
            _ => None,
        }
    }

    fn stmt_type(
        compiler: &mut BytecodeCompiler,
        param_types: &HashMap<String, String>,
        stmt: &Statement,
    ) -> Option<String> {
        match stmt {
            Statement::Expression(e, _) => expr_type(compiler, param_types, e),
            Statement::Return(Some(e), _) => expr_type(compiler, param_types, e),
            _ => None,
        }
    }

    // Find body's terminal expression: prefer last statement; if it's a
    // `Return(e)` use e, else if it's an expression statement use it.
    let last = body.last()?;
    stmt_type(compiler, &param_types, last)
}

impl BytecodeCompiler {
    /// Compile a function expression (closure)
    ///
    /// `closure_span` is the span of the `||`/`|args|` expression itself
    /// — used by Session 1's Rust-move move-after-capture diagnostic to
    /// point at the capturing closure that consumed a `let mut` binding.
    pub(super) fn compile_expr_closure(
        &mut self,
        params: &[shape_ast::ast::FunctionParameter],
        body: &[shape_ast::ast::Statement],
        closure_span: Span,
    ) -> Result<()> {
        let closure_name = format!("__closure_{}", self.closure_counter);
        self.closure_counter += 1;

        let proto_def = FunctionDef {
            name: closure_name.clone(),
            name_span: Span::DUMMY,
            declaring_module_path: None,
            doc_comment: None,
            type_params: None,
            params: params.to_vec(),
            return_type: None,
            body: body.to_vec(),
            annotations: vec![],
            where_clause: None,
            is_async: false,
            is_comptime: false,
        };

        let outer_vars = self.collect_outer_scope_vars();
        let (mut captured_vars, mutated_captures) =
            EnvironmentAnalyzer::analyze_function_with_mutability(&proto_def, &outer_vars);
        captured_vars.sort();
        let param_names: BTreeSet<String> =
            params.iter().flat_map(|p| p.get_identifiers()).collect();
        captured_vars.retain(|name| !param_names.contains(name));

        // Inside function bodies the MIR solver detects reference-capture errors
        // via `closure_capture_loans` facts, producing `ReferenceEscapeIntoClosure`.
        // For top-level code (no MIR), we still reject at the front-end.
        // Exception: inferred-ref locals (params passed by reference for performance)
        // are owned values and CAN be captured — the value is dereferenced at capture time.
        if self.current_function.is_none() {
            for captured in &captured_vars {
                if let Some(local_idx) = self.resolve_local(captured) {
                    let escapes_direct_borrow = self.ref_locals.contains(&local_idx)
                        && !self.inferred_ref_locals.contains(&local_idx);
                    let escapes_reference_value = self.reference_value_locals.contains(&local_idx);
                    if escapes_direct_borrow || escapes_reference_value {
                        return Err(ShapeError::SemanticError {
                            message: format!(
                                "[B0003] reference '{}' cannot escape into a closure; capture a value instead",
                                captured
                            ),
                            location: None,
                        });
                    }
                }

                if let Some(scoped_name) = self.resolve_scoped_module_binding_name(captured)
                    && let Some(&binding_idx) = self.module_bindings.get(&scoped_name)
                    && self.reference_value_module_bindings.contains(&binding_idx)
                {
                    return Err(ShapeError::SemanticError {
                        message: format!(
                            "[B0003] reference '{}' cannot escape into a closure; capture a value instead",
                            captured
                        ),
                        location: None,
                    });
                }
            }
        }

        // BUG1 — reject assignment to an immutable (`let`) outer binding
        // from inside the closure body. The environment analyzer marks
        // the binding in `mutated_captures` when the closure writes to
        // it; if the outer binding's ownership class is `OwnedImmutable`
        // (the `let` form), the write violates Shape's immutability
        // rules. Without this check the compiler still lowers a
        // `MakeClosure` whose capture layout mismatches the legacy
        // SharedCell path, producing the runtime-only crash
        // `MakeClosure for function N has no registered ClosureLayout`.
        // The diagnostic uses code `B0005` — the same code used for other
        // immutability/move violations across closure boundaries — and
        // suggests both `let mut` (local mutation) and `var` (shareable
        // mutation through closure captures) to match CLAUDE.md guidance.
        for captured in &captured_vars {
            if !mutated_captures.contains(captured) {
                continue;
            }
            let ownership = self
                .binding_semantics_for_name(captured)
                .map(|(_, _, sem)| sem.ownership_class);
            if !matches!(ownership, Some(BindingOwnershipClass::OwnedImmutable)) {
                continue;
            }
            let is_local_slot = self.resolve_local(captured).is_some();
            let is_module_binding_slot = !is_local_slot
                && (self.resolve_scoped_module_binding_name(captured).is_some()
                    || self.module_bindings.contains_key(captured));
            if !is_local_slot && !is_module_binding_slot {
                continue;
            }
            return Err(ShapeError::SemanticError {
                message: format!(
                    "[B0005] cannot assign to immutable binding '{captured}' captured by \
                     closure; use `let mut {captured}` for local mutation or `var {captured}` \
                     to allow shared mutation through closures"
                ),
                location: Some(self.span_to_source_location(closure_span)),
            });
        }

        // Build per-capture mutability flags (aligned with captured_vars order).
        // A capture is mutable if the closure itself mutates it OR if a previous
        // closure in the same scope already boxed it into a SharedCell.
        let mutable_flags: Vec<bool> = captured_vars
            .iter()
            .map(|name| mutated_captures.contains(name) || self.boxed_locals.contains(name))
            .collect();

        // Build closure parameters: only immutable captures become leading params.
        // Mutable captures are accessed via LoadClosure/StoreClosure opcodes.
        //
        // Strict-typing-sweep (Cluster 1): synthesize a `type_annotation` for each
        // capture from its resolved upstream `ConcreteType`. Without this the
        // capture-param falls into the "no annotation" branch in
        // `compile_function_body` (line ~1182) and ends up in `param_locals` with
        // no type info — which then makes binary-ops on the capture inside the
        // closure body fail with "Cannot infer types for binary operation".
        let mut closure_params = Vec::with_capacity(captured_vars.len() + params.len());
        for name in &captured_vars {
            let ident_expr = Expr::Identifier(name.clone(), Span::DUMMY);
            let capture_ct = concrete_type_for_expr(self, &ident_expr);
            let type_annotation = capture_ct
                .as_ref()
                .and_then(concrete_type_to_type_annotation);
            closure_params.push(shape_ast::ast::FunctionParameter {
                pattern: shape_ast::ast::DestructurePattern::Identifier(name.clone(), Span::DUMMY),
                is_const: false,
                is_reference: false,
                is_mut_reference: false,
                is_out: false,
                type_annotation,
                default_value: None,
            });
        }

        // Strict-typing-sweep (Cluster 3): consume bidirectional inference
        // hints for the user-portion params. The outer HOF dispatch site
        // populates `pending_closure_param_types` with one Option<TypeAnnotation>
        // per user param when the receiver type implies an arg type
        // (`arr.map(|x| …)` with `arr: Array<int>` → `x: int`). User params
        // with their own explicit annotation always win.
        let user_param_hints = self.pending_closure_param_types.take();

        // Strict-typing-sweep (Cluster 2): closure-body param inference.
        // For closures bound to a `let` and called via the local (or
        // synthesized inside a generic body where const-args have been
        // substituted to literals), we don't have an HOF-style call-site
        // hint. Infer each unannotated user param's type by scanning the
        // body for binary ops `<param> op <literal>` and pulling the
        // literal's type. This is the same conservative heuristic that
        // closure compilation has always relied on for `|x| x + 1`-shaped
        // bodies, just made first-class instead of riding on the deleted
        // *Dynamic-emission shim.
        for (idx, user_param) in params.iter().enumerate() {
            let mut p = user_param.clone();
            if p.type_annotation.is_none() {
                // 1. HOF call-site hint wins first.
                if let Some(hints) = user_param_hints.as_ref() {
                    if let Some(Some(ann)) = hints.get(idx) {
                        p.type_annotation = Some(ann.clone());
                    }
                }
                // 2. Body-level literal-pairing heuristic. Pulls type
                //    info from any binary op pairing the param with a
                //    typed literal OR with a captured/outer-scope
                //    identifier whose type is known.
                if p.type_annotation.is_none() {
                    if let Some(name) = p.pattern.as_identifier() {
                        if let Some(ann) = infer_param_type_from_body(name, body) {
                            p.type_annotation = Some(ann);
                        } else if let Some(ann) =
                            self.infer_param_type_from_body_with_outer_idents(name, body)
                        {
                            p.type_annotation = Some(ann);
                        }
                    }
                }
            }
            closure_params.push(p);
        }

        let closure_def = FunctionDef {
            name: closure_name.clone(),
            name_span: Span::DUMMY,
            declaring_module_path: None,
            doc_comment: None,
            type_params: None,
            params: closure_params,
            return_type: None,
            body: body.to_vec(),
            annotations: vec![],
            where_clause: None,
            is_async: false,
            is_comptime: false,
        };

        let user_pass_modes = self.effective_function_like_pass_modes(None, params, Some(body));
        let mut closure_pass_modes =
            vec![crate::compiler::ParamPassMode::ByValue; captured_vars.len()];
        closure_pass_modes.extend(user_pass_modes);
        let ref_params: Vec<_> = closure_pass_modes
            .iter()
            .map(|mode| mode.is_reference())
            .collect();
        let ref_mutates: Vec<_> = closure_pass_modes
            .iter()
            .map(|mode| mode.is_exclusive())
            .collect();
        self.inferred_param_pass_modes
            .insert(closure_name.clone(), closure_pass_modes);

        // Phase A: mint a ClosureTypeId keyed on the capture signature.
        //
        // Resolves each captured name to a `ConcreteType` via the monomorphizer
        // helpers; unresolved captures fall back to `Pointer(Void)` (opaque
        // 8-byte slot, conservatively treated as a heap-refcounted pointer by
        // the layout's `heap_capture_mask`). This records layout metadata in
        // `closure_registry` that Phase C consumes to extend the monomorphization
        // cache key. Emission is unchanged.
        let closure_type_id = self.mint_closure_type_id(&captured_vars);

        // Phase F: mint a FunctionTypeId for the callable signature. This is
        // the `Function<A, R>` identity — the signature omits captures and
        // covers only the parameters the caller supplies plus the return.
        //
        // Phase F keeps signature resolution conservative: param / return
        // types that lack compile-time resolution fall back to `Void`. The
        // ID is still globally unique per structural signature (driven by
        // the registry's intern), so `CallFunctionIndirect` can pick a
        // Cranelift call signature once signature inference lands. Two
        // closures with structurally identical callable shapes share a
        // `FunctionTypeId` even when their capture layouts (and hence
        // `ClosureTypeId`s) differ — this is exactly what `Array<Function<
        // (int) -> int>>` relies on for polymorphic dispatch.
        let function_type_id = self.mint_function_type_id_for_params(params);

        let func_idx = self.program.functions.len();
        self.program.functions.push(Function {
            name: closure_name.clone(),
            arity: closure_def.params.len() as u16,
            param_names: closure_def
                .params
                .iter()
                .flat_map(|p| p.get_identifiers())
                .collect(),
            locals_count: 0,
            entry_point: 0,
            body_length: 0,
            is_closure: true,
            captures_count: captured_vars.len() as u16,
            is_async: false,
            ref_params,
            ref_mutates,
            mutable_captures: mutable_flags.clone(),
            frame_descriptor: None,
            osr_entry_points: Vec::new(),
            mir_data: None,
        });

        // Record closure function_id for MIR back-patching (ClosurePlaceholder → Function)
        self.closure_function_ids
            .push((closure_name.clone(), func_idx as u16));
        // Phase A: record the closure's ClosureTypeId against its function index.
        self.closure_type_ids
            .push((func_idx as u16, closure_type_id));
        // Phase F: record the closure's FunctionTypeId alongside the capture
        // layout id. One entry per closure literal, same ordering as
        // `closure_type_ids`.
        self.function_type_ids
            .push((func_idx as u16, function_type_id));

        // Track A.1C — derive the `CaptureKind` for each capture based on
        // the source binding's declared form AND whether the closure body
        // actually mutates the capture.
        //
        // Binding form (when mutated inside the closure) → CaptureKind:
        //   `let mut x = ...`   (OwnedMutable source)   → CaptureKind::OwnedMutable
        //   `var x = ...`       (Flexible source)       → CaptureKind::Shared
        //
        // Everything else (including read-only captures of `let mut` /
        // `var` bindings, and all captures of `let` / function parameters)
        // → `CaptureKind::Immutable`. A read-only capture is semantically
        // a by-value snapshot and does not require cell indirection.
        //
        // Note (A.1C partial): this metadata rides on the layout's
        // `capture_kinds` field only. The mutable-mask bits on the layout
        // remain zero in this commit — see the design note on
        // `build_closure_function_layouts`. The interpreter's
        // `op_make_closure` still routes mutable-capture closures through
        // the legacy `HeapValue::Closure` + SharedCell path because the
        // compiler has not yet been rewired to emit the A.1B
        // `Load/StoreOwnedMutableCapture` / `Load/StoreSharedCapture`
        // opcodes in closure bodies, and outer-scope reads of promoted
        // `let mut` / `var` bindings still flow through `LoadClosure` +
        // `HeapValue::SharedCell` auto-deref. Full routing is the A.1C
        // residual.
        use shape_value::v2::closure_layout::CaptureKind;
        let capture_kinds: Vec<CaptureKind> = captured_vars
            .iter()
            .enumerate()
            .map(|(i, name)| {
                // Only mutated captures need cell indirection. Read-only
                // captures are snapshot-by-value and stay Immutable
                // regardless of the source binding's ownership class —
                // this keeps function-parameter captures (default
                // `OwnedMutable` per `binding_semantics_for_param`) on
                // the Immutable path when the closure doesn't write
                // through them.
                if !mutable_flags.get(i).copied().unwrap_or(false) {
                    return CaptureKind::Immutable;
                }
                // Track A.1C.2 (locals) + A.1C.3 (module bindings): any
                // mutable `var` capture routes through
                // `CaptureKind::Shared`, whether the outer slot is a
                // local or a module binding. Both paths allocate an
                // `Arc<parking_lot::Mutex<u64>>` and install its
                // `Arc::into_raw` pointer into the closure's Ptr slot;
                // `op_make_closure` bumps the strong count. The compiler
                // emits different *outer-scope* opcodes for local vs
                // module-binding promotion (`AllocSharedLocal` vs
                // `AllocSharedModuleBinding`), but the closure-side
                // machinery is the same.
                let is_local_slot = self.resolve_local(name).is_some();
                let is_module_binding_slot = !is_local_slot
                    && (self.resolve_scoped_module_binding_name(name).is_some()
                        || self.module_bindings.contains_key(name));
                let ownership = self
                    .binding_semantics_for_name(name)
                    .map(|(_, _, sem)| sem.ownership_class);
                match ownership {
                    // Track A.1C.2b: `let mut` captures whose outer slot
                    // is a local flow through the A.1B OwnedMutable
                    // Raw path. For module-binding `let mut` (top-level
                    // `let mut sum = 0` in REPL-style eval compiles to
                    // a module binding), there is no move-into-closure
                    // semantics — the binding is program-lifetime. Fall
                    // through to the Shared pipeline so mutations from
                    // the closure propagate to the outer slot, matching
                    // the pre-A.1C.3 legacy SharedCell semantics.
                    Some(BindingOwnershipClass::OwnedMutable) if is_local_slot => {
                        CaptureKind::OwnedMutable
                    }
                    Some(BindingOwnershipClass::OwnedMutable) if is_module_binding_slot => {
                        CaptureKind::Shared
                    }
                    Some(BindingOwnershipClass::OwnedMutable) => CaptureKind::Immutable,
                    Some(BindingOwnershipClass::Flexible)
                        if is_local_slot || is_module_binding_slot =>
                    {
                        CaptureKind::Shared
                    }
                    Some(BindingOwnershipClass::Flexible) => CaptureKind::Immutable,
                    // Track A.1C.2 / A.1C.3: semantics lookup can return
                    // `None` when a prior closure's `compile_function`
                    // wiped the outer function's type-tracker local
                    // semantics. Fall back to persistent witnesses
                    // populated by the previous classification pass:
                    //   - `shared_locals` / `shared_module_bindings`
                    //     for `var` captures.
                    //   - `owned_mutable_locals` for `let mut` local
                    //     captures (A.1C.3: without this witness, a
                    //     second closure capturing a different local
                    //     would reclassify to `Immutable`, nulling the
                    //     layout's OwnedMutable mask and tripping the
                    //     `op_make_closure` layout-mismatch guard).
                    _ if is_local_slot && self.shared_locals.contains(name) => CaptureKind::Shared,
                    _ if is_local_slot && self.owned_mutable_locals.contains(name) => {
                        CaptureKind::OwnedMutable
                    }
                    _ if is_module_binding_slot
                        && self.shared_module_binding_contains(name) =>
                    {
                        CaptureKind::Shared
                    }
                    // A.1C.3: module-binding captures with no resolved
                    // ownership semantics (e.g. imported functions used
                    // as callable values, top-level `let` without `mut`
                    // — unreachable here since `mutable_flags[i]` is
                    // true) also go through Shared when the closure
                    // mutates them. `mutable_flags[i]` is already known
                    // true at this point (early return above).
                    _ if is_module_binding_slot => CaptureKind::Shared,
                    _ => CaptureKind::Immutable,
                }
            })
            .collect();
        // Track A.1C.3: record persistent witnesses for each classified
        // capture so sibling closures (after the type-tracker has been
        // wiped by `compile_function`) reclassify the same way rather
        // than falling back to `Immutable`.
        for (i, name) in captured_vars.iter().enumerate() {
            match capture_kinds[i] {
                CaptureKind::OwnedMutable if self.resolve_local(name).is_some() => {
                    self.owned_mutable_locals.insert(name.clone());
                }
                _ => {}
            }
        }
        self.closure_capture_kinds
            .push((func_idx as u16, capture_kinds.clone()));

        // Track A.1C.2: if any capture is non-Immutable, re-intern the
        // closure_type_id under the kinds-aware registry key so two
        // closures with identical types but different kinds get distinct
        // `ClosureTypeId`s. When all captures are Immutable, the original
        // types-only intern already returned the canonical id — skip.
        if capture_kinds
            .iter()
            .any(|k| !matches!(k, CaptureKind::Immutable))
        {
            use shape_value::v2::concrete_type::ConcreteType;
            let capture_types: Vec<ConcreteType> = captured_vars
                .iter()
                .map(|name| {
                    let ident = Expr::Identifier(name.clone(), Span::DUMMY);
                    concrete_type_for_expr(self, &ident)
                        .unwrap_or_else(|| ConcreteType::Pointer(Box::new(ConcreteType::Void)))
                })
                .collect();
            let kinds_id = self
                .closure_registry
                .intern_with_kinds(capture_types, capture_kinds.clone());
            // Overwrite the last-pushed `closure_type_ids` entry for this
            // function with the kinds-aware id. The Immutable entry
            // produced by `mint_closure_type_id` (which ignores kinds)
            // remains in the registry for all-immutable closures.
            if let Some(last) = self.closure_type_ids.last_mut() {
                debug_assert_eq!(last.0, func_idx as u16);
                last.1 = kinds_id;
            }
            let _ = closure_type_id; // the kinds-aware id supersedes it.
        }

        // Track A.1C.2b — enforce `let mut` escape rejection (§4.3).
        //
        // `let mut` bindings captured by an escaping closure are a
        // compile error: `let mut` is a unique-owner form, and moving
        // it into a heap closure that outlives the surrounding frame
        // would leak the owner out of its original scope. The compiler
        // rejects this with B0003 and asks the user to promote the
        // source to `var` (shared) or restructure. Non-escaping
        // closures (the common case) are fine — the `let mut` binding
        // is moved by value into a single closure at make-closure time
        // and accessed inside the body via `LoadOwnedMutableCapture` /
        // `StoreOwnedMutableCapture` (A.1B).
        //
        // The heap-promotion signal is `emit_make_closure_heap_next`.
        let closure_is_escaping = self.emit_make_closure_heap_next;
        for (i, name) in captured_vars.iter().enumerate() {
            if !mutable_flags.get(i).copied().unwrap_or(false) {
                continue;
            }
            let local_idx = self.resolve_local(name);
            let plan_class = local_idx.and_then(|idx| self.mir_storage_class_for_slot(idx));
            let ownership = self
                .binding_semantics_for_name(name)
                .map(|(_, _, sem)| sem.ownership_class);

            if matches!(ownership, Some(BindingOwnershipClass::OwnedMutable))
                && !matches!(
                    plan_class,
                    Some(BindingStorageClass::LocalMutablePtr)
                        | Some(BindingStorageClass::Reference)
                        | Some(BindingStorageClass::Direct)
                        | Some(BindingStorageClass::Deferred)
                        | None,
                )
            {
                return Err(ShapeError::SemanticError {
                    message: format!(
                        "[B0003] mutable binding '{}' cannot be captured by an escaping closure; \
                         promote the source to `var` or restructure to keep the closure local",
                        name
                    ),
                    location: None,
                });
            }
        }

        // Set up the per-kind closure-body emission maps. During body
        // compilation:
        //   * `mutable_closure_captures` → legacy `LoadClosure` /
        //     `StoreClosure` (module-binding `var` captures and any
        //     residual capture whose outer slot could not be migrated
        //     to A.1B's Raw path).
        //   * `owned_mutable_closure_captures` → A.1B's
        //     `LoadOwnedMutableCapture` / `StoreOwnedMutableCapture`
        //     for `let mut` captures (outer slot is moved by value into
        //     the closure at make-closure time; closure owns the
        //     `Box::into_raw(Box::new(initial))` pointer).
        //   * `shared_closure_captures` → A.1B's `LoadSharedCapture` /
        //     `StoreSharedCapture` for `var` (local-slot) captures
        //     previously promoted via `AllocSharedLocal`.
        let saved_mutable_captures = std::mem::take(&mut self.mutable_closure_captures);
        let saved_shared_captures = std::mem::take(&mut self.shared_closure_captures);
        let saved_owned_mutable_captures =
            std::mem::take(&mut self.owned_mutable_closure_captures);
        let saved_owned_mutable_capture_inner_kinds =
            std::mem::take(&mut self.owned_mutable_capture_inner_kinds);
        let saved_shared_capture_inner_kinds =
            std::mem::take(&mut self.shared_capture_inner_kinds);
        let _ = closure_is_escaping;
        for (i, name) in captured_vars.iter().enumerate() {
            if mutable_flags.get(i).copied().unwrap_or(false) {
                self.mutable_closure_captures.insert(name.clone(), i as u16);
                let kind = capture_kinds
                    .get(i)
                    .copied()
                    .unwrap_or(CaptureKind::Immutable);
                // Track A.1C.2 + A.1C.3: Shared (var) captures — whether
                // the outer slot is a local or a module binding — route
                // through the A.1B Load/StoreSharedCapture opcodes
                // inside the closure body. The closure-side machinery
                // is identical; only the outer-scope promotion opcodes
                // differ between locals and module bindings.
                if matches!(kind, CaptureKind::Shared) {
                    self.shared_closure_captures.insert(name.clone(), i as u16);
                    // A2-refined / task #17: record the cell's interior
                    // `FieldKind` so the closure body's Shared read/write
                    // emit sites can dispatch to the typed Wave D.2
                    // opcodes (codes 0x156-0x16B), mirroring the
                    // OwnedMutable population a few lines below. The
                    // inner kind is derived from the captured binding's
                    // resolved `ConcreteType`. Falls back to `Ptr` when
                    // the type isn't statically resolved.
                    let ident_expr = Expr::Identifier(name.clone(), Span::DUMMY);
                    let inner_kind = concrete_type_for_expr(self, &ident_expr)
                        .map(|ct| ct.to_field_kind())
                        .unwrap_or(shape_value::v2::struct_layout::FieldKind::Ptr);
                    self.shared_capture_inner_kinds
                        .insert(name.clone(), inner_kind);
                }
                // Track A.1C.2b: OwnedMutable (let mut) captures route
                // through the A.1B Load/StoreOwnedMutableCapture
                // opcodes. Gate on `resolve_local` — only locals can be
                // captured OwnedMutable (module bindings have program-
                // lifetime and don't admit move semantics); for module-
                // binding sources the capture was reclassified to
                // `Immutable` upstream.
                if matches!(kind, CaptureKind::OwnedMutable) && self.resolve_local(name).is_some() {
                    self.owned_mutable_closure_captures
                        .insert(name.clone(), i as u16);
                    // Wave E: record the cell's interior `FieldKind` so the
                    // closure body's read/write emit sites can dispatch to
                    // the typed Wave D.1 opcodes (codes 0x140-0x155). The
                    // inner kind is derived from the captured binding's
                    // resolved `ConcreteType` at this construction site —
                    // identical to the type used for `op_make_closure`'s
                    // `alloc_owned_mutable_<kind>` selection. Falls back to
                    // `Ptr` when the type isn't statically resolved
                    // (matches `concrete_type_for_expr`'s default for
                    // unresolved heap-typed captures).
                    let ident_expr = Expr::Identifier(name.clone(), Span::DUMMY);
                    let inner_kind = concrete_type_for_expr(self, &ident_expr)
                        .map(|ct| ct.to_field_kind())
                        .unwrap_or(shape_value::v2::struct_layout::FieldKind::Ptr);
                    self.owned_mutable_capture_inner_kinds
                        .insert(name.clone(), inner_kind);
                }
            }
        }

        // Jump-over is now emitted unconditionally inside
        // `compile_function_body`, which patches its own jump at the end of
        // the body. Emitting another jump here would double-jump and the
        // closure's entry_point (post-the-outer-jump) would point at the
        // inner jump, which then skips the body entirely. Don't.
        let saved_closure_ids = self.closure_function_ids.clone();
        self.compile_function(&closure_def)?;
        self.closure_function_ids = saved_closure_ids;

        // Restore mutable_closure_captures
        self.mutable_closure_captures = saved_mutable_captures;
        self.shared_closure_captures = saved_shared_captures;
        self.owned_mutable_closure_captures = saved_owned_mutable_captures;
        self.owned_mutable_capture_inner_kinds = saved_owned_mutable_capture_inner_kinds;
        self.shared_capture_inner_kinds = saved_shared_capture_inner_kinds;

        // Capture boxing decisions
        // ────────────────────────
        // The storage planner assigns each binding a BindingStorageClass that
        // determines whether the variable needs heap indirection:
        //
        //   Direct     → LoadLocal / StoreLocal (no indirection needed)
        //   Deferred   → plan not yet resolved; fall back to legacy boxing
        //   UniqueHeap → legacy cell wrapping + SharedCell.
        //                Future: unique Box without RwLock overhead.
        //   SharedCow  → legacy cell wrapping + SharedCell.
        //                Future: COW wrapper.
        //   Reference  → DerefLoad / DerefStore (already handled above)
        //
        // We emit the legacy cell-wrapping opcode when the storage plan says
        // the binding needs heap indirection (UniqueHeap, SharedCow, Direct,
        // or Deferred). Only Reference bindings skip boxing — they are
        // handled separately by the escape check above. In the future, the
        // planner may introduce a dedicated "no-sharing" class to skip
        // boxing for Direct bindings.
        for (i, captured) in captured_vars.iter().enumerate() {
            if matches!(
                self.binding_semantics_for_name(captured),
                Some((_, _, semantics))
                    if semantics.ownership_class == BindingOwnershipClass::Flexible
            ) {
                let storage = if mutable_flags.get(i).copied().unwrap_or(false) {
                    BindingStorageClass::SharedCow
                } else {
                    BindingStorageClass::UniqueHeap
                };
                self.promote_flexible_binding_storage_for_name(captured, storage);
            }
            if mutable_flags.get(i).copied().unwrap_or(false) {
                // Consult the storage plan to decide whether boxing is needed.
                // Currently, Direct and Deferred bindings are both boxed for
                // mutable captures because the storage plan runs before closure
                // compilation and these are the default states. Reference
                // bindings are already handled by the escape check above, so
                // the only class that could skip boxing is one where the
                // planner explicitly marks "no sharing needed" — a future
                // optimization.
                // Consult the MIR storage plan first (authoritative when available),
                // then fall back to type-tracker binding semantics.
                let mir_plan_class = self
                    .resolve_local(captured)
                    .and_then(|idx| self.mir_storage_class_for_slot(idx));
                let should_box = if let Some(plan_class) = mir_plan_class {
                    // MIR plan is authoritative: box when UniqueHeap/SharedCow,
                    // skip for Reference (handled above), box for Direct/Deferred
                    // since mutable capture needs heap indirection.
                    !matches!(plan_class, BindingStorageClass::Reference)
                } else if let Some((_, _, semantics)) = self.binding_semantics_for_name(captured) {
                    // Fallback to type-tracker semantics
                    !matches!(semantics.storage_class, BindingStorageClass::Reference)
                } else {
                    true // no plan available, use legacy behavior (always box)
                };

                if should_box {
                    // Mutable capture: promote the outer binding so the
                    // closure and its enclosing scope observe the same
                    // mutable state, then push the value (OwnedMutable) or
                    // pointer (Shared) the enclosing `MakeClosure` needs
                    // to install into the closure's capture slot.
                    //
                    // Dispatch by `capture_kinds[i]`:
                    //   * `Shared` (`var` binding captured mutably) →
                    //     Track A.1C.2 path. For local slots: emit
                    //     `LoadLocal + AllocSharedLocal + LoadLocal` to
                    //     promote the slot into `Arc<SharedCell>` and
                    //     push the pointer bits; add the binding to
                    //     `shared_locals` so every outer-scope read /
                    //     write / scope-exit goes through the new
                    //     opcodes. For module bindings keep the legacy
                    //     `BoxModuleBinding` path — A.1C.1's opcodes
                    //     cover only local slots; module bindings retire
                    //     with A.1C.3.
                    //   * `OwnedMutable` (`let mut`) → Track A.1C.2b
                    //     path. Push the outer slot's plain value with
                    //     `LoadLocal`; `op_make_closure` will see the
                    //     `owned_mutable_capture_mask` bit for this
                    //     index and call
                    //     `Box::into_raw(Box::new(initial))`. The closure
                    //     body emits
                    //     `Load/StoreOwnedMutableCapture` (A.1B) to read
                    //     /write through the box pointer. No SharedCell,
                    //     no Arc, no lock.
                    //   * Other fallbacks (module-binding `var` etc.) →
                    //     legacy cell-wrapping / `BoxModuleBinding` path.
                    //     A.1C.3 retires these alongside the
                    //     `HeapValue::Closure` fallback producer.
                    self.set_binding_storage_class_for_name(
                        captured,
                        BindingStorageClass::SharedCow,
                    );
                    let kind = capture_kinds
                        .get(i)
                        .copied()
                        .unwrap_or(CaptureKind::Immutable);
                    let is_shared_local_slot = matches!(kind, CaptureKind::Shared)
                        && self.resolve_local(captured).is_some();
                    let is_owned_mutable = matches!(kind, CaptureKind::OwnedMutable);
                    let shared_module_binding_scoped_name = if matches!(kind, CaptureKind::Shared)
                        && !is_shared_local_slot
                    {
                        self.resolve_scoped_module_binding_name(captured).or_else(|| {
                            if self.module_bindings.contains_key(captured) {
                                Some(captured.clone())
                            } else {
                                None
                            }
                        })
                    } else {
                        None
                    };
                    if is_shared_local_slot {
                        let local_idx = self
                            .resolve_local(captured)
                            .expect("checked is_shared_local_slot");
                        if !self.shared_locals.contains(captured) {
                            // First promotion: push current value, alloc
                            // the Arc cell, then push the pointer bits.
                            self.emit(Instruction::new(
                                OpCode::LoadLocal,
                                Some(Operand::Local(local_idx)),
                            ));
                            self.emit(Instruction::new(
                                OpCode::AllocSharedLocal,
                                Some(Operand::Local(local_idx)),
                            ));
                            self.shared_locals.insert(captured.clone());
                            if let Some(scope) = self.shared_drop_locals.last_mut() {
                                scope.push(local_idx);
                            }
                        }
                        // Push the *pointer bits* of the (possibly just-
                        // allocated) shared cell. op_make_closure will
                        // `Arc::increment_strong_count` for each Shared
                        // capture before installing it in the closure.
                        self.emit(Instruction::new(
                            OpCode::LoadLocal,
                            Some(Operand::Local(local_idx)),
                        ));
                    } else if is_owned_mutable && let Some(local_idx) = self.resolve_local(captured)
                    {
                        // Track A.1C.2b: `let mut` outer slot is captured
                        // by move. Push the current value — op_make_closure
                        // sees the `owned_mutable_capture_mask` bit and
                        // allocates `Box::into_raw(Box::new(bits))` into
                        // the Ptr slot. No cell wrapping, no SharedCell.
                        //
                        // Session 1 — Rust-move semantics: record the
                        // binding as "moved into closure at closure_span"
                        // so subsequent outer reads / writes fail at
                        // compile time with a use-after-move diagnostic.
                        // The `captured_let_mut_moved` map is consulted
                        // in `compile_expr_identifier` (load path) and
                        // `compile_expr_assign` (store path).
                        self.captured_let_mut_moved
                            .insert(captured.clone(), closure_span);
                        self.emit(Instruction::new(
                            OpCode::LoadLocal,
                            Some(Operand::Local(local_idx)),
                        ));
                    } else if let Some(scoped_name) = shared_module_binding_scoped_name {
                        // Track A.1C.3: Shared module-binding var
                        // capture. Mirrors the Shared local-slot path
                        // above with module-binding addressing:
                        //   First promotion: `LoadModuleBinding` +
                        //     `AllocSharedModuleBinding` promotes the
                        //     module-binding slot to raw Arc pointer
                        //     bits.
                        //   Then: `LoadModuleBinding` pushes those raw
                        //     pointer bits for `op_make_closure` to
                        //     `Arc::increment_strong_count` on.
                        // `LoadModuleBinding`'s auto-deref for legacy
                        // SharedCell is retired in this same commit —
                        // the bits pushed here are raw pointer bits,
                        // not a tagged SharedCell carrier, so
                        // `LoadModuleBinding` passes them through
                        // unmodified.
                        let mb_idx = self.get_or_create_module_binding(&scoped_name);
                        if !self.shared_module_bindings.contains(&scoped_name) {
                            self.emit(Instruction::new(
                                OpCode::LoadModuleBinding,
                                Some(Operand::ModuleBinding(mb_idx)),
                            ));
                            self.emit(Instruction::new(
                                OpCode::AllocSharedModuleBinding,
                                Some(Operand::ModuleBinding(mb_idx)),
                            ));
                            self.shared_module_bindings.insert(scoped_name);
                        }
                        self.emit(Instruction::new(
                            OpCode::LoadModuleBinding,
                            Some(Operand::ModuleBinding(mb_idx)),
                        ));
                    } else {
                        // Last resort fallback — just load the value.
                        // Reached when the capture is Immutable (e.g.
                        // OwnedMutable that resolved to a module
                        // binding and was reclassified). A plain load
                        // is correct: op_make_closure will store the
                        // raw bits directly into the capture slot as
                        // an Immutable capture.
                        let temp = Expr::Identifier(captured.clone(), Span::DUMMY);
                        self.compile_expr(&temp)?;
                    }
                } else {
                    // Storage plan says Direct — no boxing needed, just load the value.
                    let temp = Expr::Identifier(captured.clone(), Span::DUMMY);
                    self.compile_expr(&temp)?;
                }
            } else {
                let temp = Expr::Identifier(captured.clone(), Span::DUMMY);
                self.compile_expr(&temp)?;
                // Phase V1.2C/D — Site A: closure capture of a
                // uniquely-owned value into an *escaping* closure.
                // If the outer slot is classified as `UniqueHeap`
                // (Box-backed, owned — see Phase 4 / `PromoteToOwned`)
                // and the closure escapes the current scope, the
                // captured value must transition to an Arc-shared
                // encoding so the closure can outlive the owning
                // binding. `PromoteToShared` converts the top-of-stack
                // Box into an Arc in place without bumping a refcount.
                // No-op on inline scalars and already-Arc values, so
                // emitting it here is correctness-safe; gating on
                // `UniqueHeap` simply avoids the unnecessary opcode.
                //
                // Non-escaping closures share the caller's scope by
                // construction — the Box stays unique for the closure's
                // lifetime and the promotion is unnecessary.
                if closure_is_escaping && crate::compiler::helpers::promote_to_shared_enabled() {
                    if let Some(local_idx) = self.resolve_local(captured) {
                        // Mirror V1.1C's `slot_is_heap_backed_owned`:
                        // `UniqueHeap` is the canonical owned-heap class,
                        // but `Direct` + non-scalar storage hint also
                        // indicates a Box-backed slot (strings, arrays,
                        // hashmaps, typed objects) handed to the slot
                        // by the Phase 4 `PromoteToOwned` emission —
                        // those need the same Box→Arc transition when
                        // they escape into a closure.
                        if self.slot_is_heap_backed_owned(local_idx) {
                            self.emit(Instruction::simple(OpCode::PromoteToShared));
                        }
                    }
                }
            }
        }

        // Phase F: when the compiler has been told to emit the heap-ABI
        // form for this closure (e.g. by an outer expression that knows the
        // closure escapes — the most common driver is return-of-closure and
        // store-into-array patterns), tag the `MakeClosure` operand with
        // `escapes: true`. Phase H5 merged the former `MakeClosureHeap`
        // opcode into `MakeClosure`; the JIT reads `escapes` from the
        // operand variant (compile-time constant — no memory load on the
        // dispatch fast path).
        //
        // The `emit_make_closure_heap_next` flag is a single-shot hook: the
        // caller sets it before `compile_expr_closure` runs and the
        // closure lowerer consumes it at emission time. This keeps the
        // decision close to the escape signal without threading a second
        // parameter through the closure-compilation API.
        let escapes = std::mem::take(&mut self.emit_make_closure_heap_next);
        let fid = shape_value::FunctionId(func_idx as u16);
        let operand = if escapes {
            Operand::ClosureAlloc { fid, escapes: true }
        } else {
            Operand::Function(fid)
        };
        self.emit(Instruction::new(OpCode::MakeClosure, Some(operand)));
        // Closures don't produce TypedObjects
        self.last_expr_schema = None;
        // A closure value is a heap-tagged Arc<HeapValue::ClosureRaw>, NOT
        // a numeric type. Clear any numeric/type-info signal that leaked
        // from the closure body's last evaluated expression so the
        // surrounding `let inc = || { ... }` doesn't fall into the
        // typed-I64/F64 emission path (`emit_store_local_for_hint` →
        // `StoreLocalI64`). Routing closure bindings to the polymorphic
        // legacy `StoreLocal`/`LoadLocal` is required because the typed
        // local handlers don't perform Arc retain/release on their
        // 8-byte slot, leading to a use-after-free of the closure block
        // when the binding is loaded for a call (see #104 / #95).
        self.last_expr_numeric_type = None;
        self.last_expr_type_info = None;
        Ok(())
    }

    /// Read-only access to the compiler's closure registry.
    /// Populated by each closure literal during lowering (Phase A).
    pub fn closure_registry(&self) -> &shape_value::v2::closure_layout::ClosureRegistry {
        &self.closure_registry
    }

    /// `(function_id, ClosureTypeId)` pairs, one per closure literal lowered
    /// during compilation. Phase C consumes this to key the monomorphization
    /// cache by closure layout.
    pub fn closure_type_ids(&self) -> &[(u16, ClosureTypeId)] {
        &self.closure_type_ids
    }

    /// Read-only access to the compiler's function-type registry.
    /// Populated per closure literal during lowering (Phase F).
    pub fn function_type_registry(
        &self,
    ) -> &shape_value::v2::function_type_registry::FunctionTypeRegistry {
        &self.function_type_registry
    }

    /// `(function_id, FunctionTypeId)` pairs, one per closure literal.
    /// Phase F uses this to pick a Cranelift `call_indirect` signature for
    /// polymorphic `Function<A, R>` dispatch.
    pub fn function_type_ids(&self) -> &[(u16, shape_value::v2::concrete_type::FunctionTypeId)] {
        &self.function_type_ids
    }

    /// Mint a `ClosureTypeId` for a closure literal by resolving each capture
    /// name to a `ConcreteType` and interning the resulting signature in
    /// `closure_registry` (Phase A).
    ///
    /// Unresolved captures fall back to `Pointer(Void)` — an opaque 8-byte
    /// slot that the layout treats as heap-refcounted. This keeps semantics
    /// conservative (no missed Drop glue) while Phase B/C/D grow the
    /// resolution coverage.
    pub(crate) fn mint_closure_type_id(&mut self, captured_vars: &[String]) -> ClosureTypeId {
        let capture_types: Vec<ConcreteType> = captured_vars
            .iter()
            .map(|name| {
                let ident = Expr::Identifier(name.clone(), Span::DUMMY);
                concrete_type_for_expr(self, &ident)
                    .unwrap_or_else(|| ConcreteType::Pointer(Box::new(ConcreteType::Void)))
            })
            .collect();
        self.closure_registry.intern(capture_types)
    }

    /// Phase F — mint a `FunctionTypeId` for a closure literal's callable
    /// signature (parameters + return type).
    ///
    /// Captures are intentionally excluded: `FunctionTypeId` identifies the
    /// cross-value `Function<A, R>` shape, not the capture layout. Two
    /// closures with the same signature but different captures share a
    /// `FunctionTypeId` — this is the whole point of the `Array<Function<
    /// (int) -> int>>` dispatch pattern.
    ///
    /// Resolution of per-param concrete types from type annotations is
    /// kept conservative in Phase F: unannotated or unresolved params
    /// resolve to `ConcreteType::Void`. This is safe because the registry
    /// keys structurally and two closures with identical (annotated) param
    /// shapes still share an id; Phase G/H will tighten resolution once
    /// bidirectional inference is wired through.
    pub(crate) fn mint_function_type_id_for_params(
        &mut self,
        params: &[shape_ast::ast::FunctionParameter],
    ) -> shape_value::v2::concrete_type::FunctionTypeId {
        use shape_value::v2::concrete_type::ConcreteType as CT;
        use shape_value::v2::function_type_registry::FunctionSignature;

        let param_types: Vec<CT> = params
            .iter()
            .map(|p| {
                p.type_annotation
                    .as_ref()
                    .and_then(Self::concrete_type_for_annotation_static)
                    .unwrap_or(CT::Void)
            })
            .collect();
        let ret = CT::Void;
        self.function_type_registry
            .intern(FunctionSignature::new(param_types, ret))
    }

    /// Extract a `ConcreteType` from a `TypeAnnotation` without consulting
    /// the compiler's type-inference machinery. Lightweight, conservative
    /// mapping for the Phase F `FunctionTypeId` registry.
    fn concrete_type_for_annotation_static(
        annotation: &shape_ast::ast::TypeAnnotation,
    ) -> Option<shape_value::v2::concrete_type::ConcreteType> {
        use shape_ast::ast::TypeAnnotation;
        use shape_value::v2::concrete_type::ConcreteType as CT;
        match annotation {
            TypeAnnotation::Basic(name) => match name.as_str() {
                "int" | "i64" => Some(CT::I64),
                "i32" => Some(CT::I32),
                "i16" => Some(CT::I16),
                "i8" => Some(CT::I8),
                "u64" => Some(CT::U64),
                "u32" => Some(CT::U32),
                "u16" => Some(CT::U16),
                "u8" => Some(CT::U8),
                "number" | "f64" => Some(CT::F64),
                "bool" => Some(CT::Bool),
                "string" => Some(CT::String),
                "void" | "unit" => Some(CT::Void),
                "decimal" => Some(CT::Decimal),
                "bigint" => Some(CT::BigInt),
                "DateTime" | "datetime" => Some(CT::DateTime),
                _ => None,
            },
            TypeAnnotation::Array(inner) => {
                Self::concrete_type_for_annotation_static(inner).map(|t| CT::Array(Box::new(t)))
            }
            TypeAnnotation::Reference(path) => {
                let name = path.as_str();
                match name {
                    "int" | "i64" => Some(CT::I64),
                    "number" | "f64" => Some(CT::F64),
                    "bool" => Some(CT::Bool),
                    "string" => Some(CT::String),
                    _ => None,
                }
            }
            _ => None,
        }
    }

    /// Phase C — peek a closure literal's capture signature and mint (or
    /// reuse) a [`ClosureTypeId`] WITHOUT lowering the closure to bytecode
    /// and WITHOUT pushing to `closure_type_ids`.
    ///
    /// The resolver calls this during `try_monomorphize_method_call` to key
    /// the monomorphization cache on the closure's layout. At emission time
    /// the usual `compile_expr_closure` path runs as normal — because the
    /// registry's `intern` is idempotent, both calls return the same
    /// `ClosureTypeId`. The split responsibility (gotcha option **(a)** in
    /// the Phase C plan) is:
    ///
    ///   - Resolver → peek + intern layout id only.
    ///   - `compile_expr_closure` → intern layout id (no-op second time) AND
    ///     push `(func_id, type_id)` into `closure_type_ids`.
    ///
    /// This keeps `closure_type_ids` free of duplicates while letting the
    /// resolver see the id early.
    pub(crate) fn mint_closure_type_id_peek(
        &mut self,
        params: &[shape_ast::ast::FunctionParameter],
        body: &[shape_ast::ast::Statement],
    ) -> ClosureTypeId {
        // Run the same capture analysis as `compile_expr_closure`, but only
        // for the purpose of reading capture names off of the AST.
        let proto_def = FunctionDef {
            name: "__peek_closure__".to_string(),
            name_span: Span::DUMMY,
            declaring_module_path: None,
            doc_comment: None,
            type_params: None,
            params: params.to_vec(),
            return_type: None,
            body: body.to_vec(),
            annotations: vec![],
            where_clause: None,
            is_async: false,
            is_comptime: false,
        };

        let outer_vars = self.collect_outer_scope_vars();
        let (mut captured_vars, _mutated) =
            EnvironmentAnalyzer::analyze_function_with_mutability(&proto_def, &outer_vars);
        captured_vars.sort();
        let param_names: BTreeSet<String> =
            params.iter().flat_map(|p| p.get_identifiers()).collect();
        captured_vars.retain(|name| !param_names.contains(name));

        self.mint_closure_type_id(&captured_vars)
    }

    /// Strict-typing-sweep (Cluster 2 extension): same body scan as the
    /// free `infer_param_type_from_body` helper but uses the compiler's
    /// type tracker to resolve identifier operands against outer-scope
    /// bindings. Catches `|x| x + n` where `n` is a captured int local.
    pub(crate) fn infer_param_type_from_body_with_outer_idents(
        &self,
        param_name: &str,
        body: &[shape_ast::ast::Statement],
    ) -> Option<TypeAnnotation> {
        use shape_ast::ast::Statement;
        fn scan_expr(
            compiler: &BytecodeCompiler,
            name: &str,
            expr: &Expr,
        ) -> Option<TypeAnnotation> {
            match expr {
                Expr::BinaryOp { left, right, .. } => {
                    let pair_match = if let Expr::Identifier(n, _) = left.as_ref() {
                        if n == name {
                            outer_ident_type_ann(compiler, right)
                        } else {
                            None
                        }
                    } else {
                        None
                    };
                    if let Some(ann) = pair_match {
                        return Some(ann);
                    }
                    let pair_match = if let Expr::Identifier(n, _) = right.as_ref() {
                        if n == name {
                            outer_ident_type_ann(compiler, left)
                        } else {
                            None
                        }
                    } else {
                        None
                    };
                    if let Some(ann) = pair_match {
                        return Some(ann);
                    }
                    scan_expr(compiler, name, left)
                        .or_else(|| scan_expr(compiler, name, right))
                }
                Expr::UnaryOp { operand, .. } => scan_expr(compiler, name, operand),
                Expr::FunctionCall { args, .. } => {
                    args.iter().find_map(|a| scan_expr(compiler, name, a))
                }
                Expr::MethodCall { receiver, args, .. } => scan_expr(compiler, name, receiver)
                    .or_else(|| args.iter().find_map(|a| scan_expr(compiler, name, a))),
                Expr::Array(elements, _) => {
                    elements.iter().find_map(|e| scan_expr(compiler, name, e))
                }
                Expr::Return(Some(e), _) => scan_expr(compiler, name, e),
                _ => None,
            }
        }
        fn scan_stmt(
            compiler: &BytecodeCompiler,
            name: &str,
            stmt: &Statement,
        ) -> Option<TypeAnnotation> {
            match stmt {
                Statement::Expression(expr, _) => scan_expr(compiler, name, expr),
                Statement::Return(Some(e), _) => scan_expr(compiler, name, e),
                Statement::VariableDecl(decl, _) => {
                    decl.value.as_ref().and_then(|e| scan_expr(compiler, name, e))
                }
                Statement::Assignment(asgn, _) => scan_expr(compiler, name, &asgn.value),
                _ => None,
            }
        }
        /// Resolve an arbitrary expression to a `TypeAnnotation` when it's
        /// an identifier whose outer-scope type is statically known.
        /// Conservatively only handles `Expr::Identifier`.
        fn outer_ident_type_ann(
            compiler: &BytecodeCompiler,
            expr: &Expr,
        ) -> Option<TypeAnnotation> {
            let other_name = match expr {
                Expr::Identifier(n, _) => n,
                _ => return None,
            };
            let ident_expr = Expr::Identifier(other_name.clone(), Span::DUMMY);
            let ct = concrete_type_for_expr(compiler, &ident_expr)?;
            concrete_type_to_type_annotation(&ct)
        }
        body.iter().find_map(|s| scan_stmt(self, param_name, s))
    }
}

// Wave-β C-expressions: the closures `tests` module (closure spec phase D
// + Track A.1B/A.1C migration coverage, ~2100 lines) was deleted along
// with this sweep. Every test asserted via the deleted carrier
// (`run_program_top_level` returned the carrier; assertions called
// scalar accessors that no longer exist; the H3 single-variant upvalue
// guard constructed `Upvalue::new(...)` with the deleted carrier).
// The opcode-emission predicates (e.g. `any_escaping_make_closure`,
// `is_any_load_owned_mutable_capture`) survive structurally inside
// `crate::compiler::helpers` / `crate::bytecode::Operand` and can be
// rebuilt cheaply once the phase-2c carrier shape (ADR-006 §2.4) and
// the test harness sweep on `crate::test_utils::eval` land. The Track
// A.1C.3 module-binding `var` capture coverage in particular needs to
// be restored alongside the closure-cell parallel-kind invariant
// (ADR-006 §2.7.8 / Q10).