harn_vm/

compiler.rs

use std::collections::BTreeMap;
use std::rc::Rc;

use harn_lexer::StringSegment;
use harn_parser::{BindingPattern, Node, ParallelMode, SNode, TypedParam};

use crate::chunk::{Chunk, CompiledFunction, Constant, Op};
use crate::schema;
use crate::value::VmValue;

/// Compile error.
#[derive(Debug)]
pub struct CompileError {
    pub message: String,
    pub line: u32,
}

impl std::fmt::Display for CompileError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "Compile error at line {}: {}", self.line, self.message)
    }
}

impl std::error::Error for CompileError {}

/// Entry in the compiler's pending-finally stack. See the field-level doc on
/// `Compiler::finally_bodies` for the unwind semantics each variant encodes.
#[derive(Clone, Debug)]
enum FinallyEntry {
    Finally(Vec<SNode>),
    CatchBarrier,
}

/// Tracks loop context for break/continue compilation.
struct LoopContext {
    /// Offset of the loop start (for continue).
    start_offset: usize,
    /// Positions of break jumps that need patching to the loop end.
    break_patches: Vec<usize>,
    /// True if this is a for-in loop (has an iterator to clean up on break).
    has_iterator: bool,
    /// Number of exception handlers active at loop entry.
    handler_depth: usize,
    /// Number of pending finally bodies at loop entry.
    finally_depth: usize,
    /// Lexical scope depth at loop entry.
    scope_depth: usize,
}

/// Compiles an AST into bytecode.
pub struct Compiler {
    chunk: Chunk,
    line: u32,
    column: u32,
    /// Track enum type names so PropertyAccess on them can produce EnumVariant.
    enum_names: std::collections::HashSet<String>,
    /// Track interface names → method names for runtime enforcement.
    interface_methods: std::collections::HashMap<String, Vec<String>>,
    /// Stack of active loop contexts for break/continue.
    loop_stack: Vec<LoopContext>,
    /// Current depth of exception handlers (for cleanup on break/continue).
    handler_depth: usize,
    /// Stack of pending finally bodies plus catch-handler barriers for
    /// unwind-aware lowering of `throw`, `return`, `break`, and `continue`.
    ///
    /// A `Finally` entry is a pending finally body that must execute when
    /// control exits its enclosing try block. A `CatchBarrier` marks the
    /// boundary of an active `try/catch` handler: throws emitted inside
    /// the try body are caught locally, so pre-running finallys *beyond*
    /// the barrier would wrongly fire side effects for outer blocks the
    /// throw never actually escapes. Throw lowering stops at the innermost
    /// barrier; `return`/`break`/`continue`, which do transfer past local
    /// handlers, still run every pending `Finally` up to their target.
    finally_bodies: Vec<FinallyEntry>,
    /// Counter for unique temp variable names.
    temp_counter: usize,
    /// Number of lexical block scopes currently active in this compiled frame.
    scope_depth: usize,
}

impl Compiler {
    pub fn new() -> Self {
        Self {
            chunk: Chunk::new(),
            line: 1,
            column: 1,
            enum_names: std::collections::HashSet::new(),
            interface_methods: std::collections::HashMap::new(),
            loop_stack: Vec::new(),
            handler_depth: 0,
            finally_bodies: Vec::new(),
            temp_counter: 0,
            scope_depth: 0,
        }
    }

    /// Compile a program (list of top-level nodes) into a Chunk.
    /// Finds the entry pipeline and compiles its body, including inherited bodies.
    pub fn compile(mut self, program: &[SNode]) -> Result<Chunk, CompileError> {
        // Pre-scan so we can recognize EnumName.Variant as enum construction
        // even when the enum is declared inside a pipeline.
        Self::collect_enum_names(program, &mut self.enum_names);
        self.enum_names.insert("Result".to_string());
        Self::collect_interface_methods(program, &mut self.interface_methods);

        for sn in program {
            match &sn.node {
                Node::ImportDecl { .. } | Node::SelectiveImport { .. } => {
                    self.compile_node(sn)?;
                }
                _ => {}
            }
        }
        let main = program
            .iter()
            .find(|sn| matches!(&sn.node, Node::Pipeline { name, .. } if name == "default"))
            .or_else(|| {
                program
                    .iter()
                    .find(|sn| matches!(&sn.node, Node::Pipeline { .. }))
            });

        if let Some(sn) = main {
            self.compile_top_level_declarations(program)?;
            if let Node::Pipeline { body, extends, .. } = &sn.node {
                if let Some(parent_name) = extends {
                    self.compile_parent_pipeline(program, parent_name)?;
                }
                self.compile_block(body)?;
            }
        } else {
            // Script mode: no pipeline found, treat top-level as implicit entry.
            let top_level: Vec<&SNode> = program
                .iter()
                .filter(|sn| {
                    !matches!(
                        &sn.node,
                        Node::ImportDecl { .. } | Node::SelectiveImport { .. }
                    )
                })
                .collect();
            for sn in &top_level {
                self.compile_node(sn)?;
                if Self::produces_value(&sn.node) {
                    self.chunk.emit(Op::Pop, self.line);
                }
            }
        }

        for fb in self.all_pending_finallys() {
            self.compile_finally_inline(&fb)?;
        }
        self.chunk.emit(Op::Nil, self.line);
        self.chunk.emit(Op::Return, self.line);
        Ok(self.chunk)
    }

    /// Compile a specific named pipeline (for test runners).
    pub fn compile_named(
        mut self,
        program: &[SNode],
        pipeline_name: &str,
    ) -> Result<Chunk, CompileError> {
        Self::collect_enum_names(program, &mut self.enum_names);
        Self::collect_interface_methods(program, &mut self.interface_methods);

        for sn in program {
            if matches!(
                &sn.node,
                Node::ImportDecl { .. } | Node::SelectiveImport { .. }
            ) {
                self.compile_node(sn)?;
            }
        }
        let target = program
            .iter()
            .find(|sn| matches!(&sn.node, Node::Pipeline { name, .. } if name == pipeline_name));

        if let Some(sn) = target {
            self.compile_top_level_declarations(program)?;
            if let Node::Pipeline { body, extends, .. } = &sn.node {
                if let Some(parent_name) = extends {
                    self.compile_parent_pipeline(program, parent_name)?;
                }
                self.compile_block(body)?;
            }
        }

        for fb in self.all_pending_finallys() {
            self.compile_finally_inline(&fb)?;
        }
        self.chunk.emit(Op::Nil, self.line);
        self.chunk.emit(Op::Return, self.line);
        Ok(self.chunk)
    }

    /// Recursively compile parent pipeline bodies (for extends).
    fn compile_parent_pipeline(
        &mut self,
        program: &[SNode],
        parent_name: &str,
    ) -> Result<(), CompileError> {
        let parent = program
            .iter()
            .find(|sn| matches!(&sn.node, Node::Pipeline { name, .. } if name == parent_name));
        if let Some(sn) = parent {
            if let Node::Pipeline { body, extends, .. } = &sn.node {
                if let Some(grandparent) = extends {
                    self.compile_parent_pipeline(program, grandparent)?;
                }
                for stmt in body {
                    self.compile_node(stmt)?;
                    if Self::produces_value(&stmt.node) {
                        self.chunk.emit(Op::Pop, self.line);
                    }
                }
            }
        }
        Ok(())
    }

    /// Emit bytecode preamble for default parameter values.
    /// For each param with a default at index i, emits:
    ///   GetArgc; PushInt (i+1); GreaterEqual; JumpIfTrue <skip>;
    ///   [compile default expr]; DefLet param_name; <skip>:
    fn emit_default_preamble(&mut self, params: &[TypedParam]) -> Result<(), CompileError> {
        for (i, param) in params.iter().enumerate() {
            if let Some(default_expr) = &param.default_value {
                self.chunk.emit(Op::GetArgc, self.line);
                let threshold_idx = self.chunk.add_constant(Constant::Int((i + 1) as i64));
                self.chunk.emit_u16(Op::Constant, threshold_idx, self.line);
                self.chunk.emit(Op::GreaterEqual, self.line);
                let skip_jump = self.chunk.emit_jump(Op::JumpIfTrue, self.line);
                // JumpIfTrue doesn't pop its boolean operand.
                self.chunk.emit(Op::Pop, self.line);
                self.compile_node(default_expr)?;
                let name_idx = self
                    .chunk
                    .add_constant(Constant::String(param.name.clone()));
                self.chunk.emit_u16(Op::DefLet, name_idx, self.line);
                let end_jump = self.chunk.emit_jump(Op::Jump, self.line);
                self.chunk.patch_jump(skip_jump);
                self.chunk.emit(Op::Pop, self.line);
                self.chunk.patch_jump(end_jump);
            }
        }
        Ok(())
    }

    /// Emit runtime type checks for parameters with type annotations.
    /// Interface types keep their dedicated runtime guard; all other supported
    /// runtime-checkable types compile to a schema literal and call
    /// `__assert_schema(value, param_name, schema)`.
    fn emit_type_checks(&mut self, params: &[TypedParam]) {
        for param in params {
            if let Some(type_expr) = &param.type_expr {
                if let harn_parser::TypeExpr::Named(name) = type_expr {
                    if let Some(methods) = self.interface_methods.get(name) {
                        let fn_idx = self
                            .chunk
                            .add_constant(Constant::String("__assert_interface".into()));
                        self.chunk.emit_u16(Op::Constant, fn_idx, self.line);
                        let var_idx = self
                            .chunk
                            .add_constant(Constant::String(param.name.clone()));
                        self.chunk.emit_u16(Op::GetVar, var_idx, self.line);
                        let name_idx = self
                            .chunk
                            .add_constant(Constant::String(param.name.clone()));
                        self.chunk.emit_u16(Op::Constant, name_idx, self.line);
                        let iface_idx = self.chunk.add_constant(Constant::String(name.clone()));
                        self.chunk.emit_u16(Op::Constant, iface_idx, self.line);
                        let methods_str = methods.join(",");
                        let methods_idx = self.chunk.add_constant(Constant::String(methods_str));
                        self.chunk.emit_u16(Op::Constant, methods_idx, self.line);
                        self.chunk.emit_u8(Op::Call, 4, self.line);
                        self.chunk.emit(Op::Pop, self.line);
                        continue;
                    }
                }

                if let Some(schema) = Self::type_expr_to_schema_value(type_expr) {
                    let fn_idx = self
                        .chunk
                        .add_constant(Constant::String("__assert_schema".into()));
                    self.chunk.emit_u16(Op::Constant, fn_idx, self.line);
                    let var_idx = self
                        .chunk
                        .add_constant(Constant::String(param.name.clone()));
                    self.chunk.emit_u16(Op::GetVar, var_idx, self.line);
                    let name_idx = self
                        .chunk
                        .add_constant(Constant::String(param.name.clone()));
                    self.chunk.emit_u16(Op::Constant, name_idx, self.line);
                    self.emit_vm_value_literal(&schema);
                    self.chunk.emit_u8(Op::Call, 3, self.line);
                    self.chunk.emit(Op::Pop, self.line);
                }
            }
        }
    }

    fn type_expr_to_schema_value(type_expr: &harn_parser::TypeExpr) -> Option<VmValue> {
        match type_expr {
            harn_parser::TypeExpr::Named(name) => match name.as_str() {
                "int" | "float" | "string" | "bool" | "list" | "dict" | "set" | "nil"
                | "closure" => Some(VmValue::Dict(Rc::new(BTreeMap::from([(
                    "type".to_string(),
                    VmValue::String(Rc::from(name.as_str())),
                )])))),
                _ => None,
            },
            harn_parser::TypeExpr::Shape(fields) => {
                let mut properties = BTreeMap::new();
                let mut required = Vec::new();
                for field in fields {
                    let field_schema = Self::type_expr_to_schema_value(&field.type_expr)?;
                    properties.insert(field.name.clone(), field_schema);
                    if !field.optional {
                        required.push(VmValue::String(Rc::from(field.name.as_str())));
                    }
                }
                let mut out = BTreeMap::new();
                out.insert("type".to_string(), VmValue::String(Rc::from("dict")));
                out.insert("properties".to_string(), VmValue::Dict(Rc::new(properties)));
                if !required.is_empty() {
                    out.insert("required".to_string(), VmValue::List(Rc::new(required)));
                }
                Some(VmValue::Dict(Rc::new(out)))
            }
            harn_parser::TypeExpr::List(inner) => {
                let mut out = BTreeMap::new();
                out.insert("type".to_string(), VmValue::String(Rc::from("list")));
                if let Some(item_schema) = Self::type_expr_to_schema_value(inner) {
                    out.insert("items".to_string(), item_schema);
                }
                Some(VmValue::Dict(Rc::new(out)))
            }
            harn_parser::TypeExpr::DictType(key, value) => {
                let mut out = BTreeMap::new();
                out.insert("type".to_string(), VmValue::String(Rc::from("dict")));
                if matches!(key.as_ref(), harn_parser::TypeExpr::Named(name) if name == "string") {
                    if let Some(value_schema) = Self::type_expr_to_schema_value(value) {
                        out.insert("additional_properties".to_string(), value_schema);
                    }
                }
                Some(VmValue::Dict(Rc::new(out)))
            }
            harn_parser::TypeExpr::Union(members) => {
                let branches = members
                    .iter()
                    .filter_map(Self::type_expr_to_schema_value)
                    .collect::<Vec<_>>();
                if branches.is_empty() {
                    None
                } else {
                    Some(VmValue::Dict(Rc::new(BTreeMap::from([(
                        "union".to_string(),
                        VmValue::List(Rc::new(branches)),
                    )]))))
                }
            }
            harn_parser::TypeExpr::FnType { .. } => {
                Some(VmValue::Dict(Rc::new(BTreeMap::from([(
                    "type".to_string(),
                    VmValue::String(Rc::from("closure")),
                )]))))
            }
            harn_parser::TypeExpr::Applied { .. } => None,
            harn_parser::TypeExpr::Iter(_) => None,
            harn_parser::TypeExpr::Never => None,
        }
    }

    fn emit_vm_value_literal(&mut self, value: &VmValue) {
        match value {
            VmValue::String(text) => {
                let idx = self.chunk.add_constant(Constant::String(text.to_string()));
                self.chunk.emit_u16(Op::Constant, idx, self.line);
            }
            VmValue::Int(number) => {
                let idx = self.chunk.add_constant(Constant::Int(*number));
                self.chunk.emit_u16(Op::Constant, idx, self.line);
            }
            VmValue::Float(number) => {
                let idx = self.chunk.add_constant(Constant::Float(*number));
                self.chunk.emit_u16(Op::Constant, idx, self.line);
            }
            VmValue::Bool(value) => {
                let idx = self.chunk.add_constant(Constant::Bool(*value));
                self.chunk.emit_u16(Op::Constant, idx, self.line);
            }
            VmValue::Nil => self.chunk.emit(Op::Nil, self.line),
            VmValue::List(items) => {
                for item in items.iter() {
                    self.emit_vm_value_literal(item);
                }
                self.chunk
                    .emit_u16(Op::BuildList, items.len() as u16, self.line);
            }
            VmValue::Dict(entries) => {
                for (key, item) in entries.iter() {
                    let key_idx = self.chunk.add_constant(Constant::String(key.clone()));
                    self.chunk.emit_u16(Op::Constant, key_idx, self.line);
                    self.emit_vm_value_literal(item);
                }
                self.chunk
                    .emit_u16(Op::BuildDict, entries.len() as u16, self.line);
            }
            _ => {}
        }
    }

    /// Emit the extra u16 type name index after a TryCatchSetup jump.
    fn emit_type_name_extra(&mut self, type_name_idx: u16) {
        let hi = (type_name_idx >> 8) as u8;
        let lo = type_name_idx as u8;
        self.chunk.code.push(hi);
        self.chunk.code.push(lo);
        self.chunk.lines.push(self.line);
        self.chunk.columns.push(self.column);
        self.chunk.lines.push(self.line);
        self.chunk.columns.push(self.column);
    }

    /// Compile a try/catch body block (produces a value on the stack).
    fn compile_try_body(&mut self, body: &[SNode]) -> Result<(), CompileError> {
        if body.is_empty() {
            self.chunk.emit(Op::Nil, self.line);
        } else {
            self.compile_scoped_block(body)?;
        }
        Ok(())
    }

    /// Compile catch error binding (error value is on stack from handler).
    fn compile_catch_binding(&mut self, error_var: &Option<String>) -> Result<(), CompileError> {
        if let Some(var_name) = error_var {
            let idx = self.chunk.add_constant(Constant::String(var_name.clone()));
            self.chunk.emit_u16(Op::DefLet, idx, self.line);
        } else {
            self.chunk.emit(Op::Pop, self.line);
        }
        Ok(())
    }

    /// Compile finally body inline, discarding its result value.
    fn compile_finally_inline(&mut self, finally_body: &[SNode]) -> Result<(), CompileError> {
        if !finally_body.is_empty() {
            self.compile_scoped_block(finally_body)?;
            if Self::produces_value(&finally_body.last().unwrap().node) {
                self.chunk.emit(Op::Pop, self.line);
            }
        }
        Ok(())
    }

    /// Collect pending finally bodies from the top of the stack down to
    /// (but not including) the innermost `CatchBarrier`. Used by `throw`
    /// lowering: throws caught locally don't unwind past the catch, so
    /// finallys behind the barrier aren't on the throw's exit path.
    fn pending_finallys_until_barrier(&self) -> Vec<Vec<SNode>> {
        let mut out = Vec::new();
        for entry in self.finally_bodies.iter().rev() {
            match entry {
                FinallyEntry::CatchBarrier => break,
                FinallyEntry::Finally(body) => out.push(body.clone()),
            }
        }
        out
    }

    /// Collect every pending finally body from the top of the stack down
    /// to `floor` (an index produced by `finally_bodies.len()` at some
    /// earlier point), skipping `CatchBarrier` markers. Used by `return`,
    /// `break`, and `continue` lowering — they transfer control past local
    /// handlers, so every `Finally` up to their target must run.
    fn pending_finallys_down_to(&self, floor: usize) -> Vec<Vec<SNode>> {
        let mut out = Vec::new();
        for entry in self.finally_bodies[floor..].iter().rev() {
            if let FinallyEntry::Finally(body) = entry {
                out.push(body.clone());
            }
        }
        out
    }

    /// All pending finally bodies (entire stack), skipping barriers.
    fn all_pending_finallys(&self) -> Vec<Vec<SNode>> {
        self.pending_finallys_down_to(0)
    }

    /// True if there are any pending finally bodies (not just barriers).
    fn has_pending_finally(&self) -> bool {
        self.finally_bodies
            .iter()
            .any(|e| matches!(e, FinallyEntry::Finally(_)))
    }

    /// Save a thrown value to a temp and rethrow without running finally.
    ///
    /// Historically this helper also invoked `compile_finally_inline` on the
    /// thrown path, but that produced observable double-runs: the
    /// `Node::ThrowStmt` lowering (below) already iterates `finally_bodies`
    /// and runs each pending finally inline *before* emitting `Op::Throw`, so
    /// a second run here fired the same side effects twice. Finally now runs
    /// exactly once — via the throw-emit path during unwinding.
    fn compile_plain_rethrow(&mut self) -> Result<(), CompileError> {
        self.temp_counter += 1;
        let temp_name = format!("__finally_err_{}__", self.temp_counter);
        let err_idx = self.chunk.add_constant(Constant::String(temp_name.clone()));
        self.chunk.emit_u16(Op::DefVar, err_idx, self.line);
        let get_idx = self.chunk.add_constant(Constant::String(temp_name));
        self.chunk.emit_u16(Op::GetVar, get_idx, self.line);
        self.chunk.emit(Op::Throw, self.line);
        Ok(())
    }

    fn begin_scope(&mut self) {
        self.chunk.emit(Op::PushScope, self.line);
        self.scope_depth += 1;
    }

    fn end_scope(&mut self) {
        if self.scope_depth > 0 {
            self.chunk.emit(Op::PopScope, self.line);
            self.scope_depth -= 1;
        }
    }

    fn unwind_scopes_to(&mut self, target_depth: usize) {
        while self.scope_depth > target_depth {
            self.chunk.emit(Op::PopScope, self.line);
            self.scope_depth -= 1;
        }
    }

    fn compile_scoped_block(&mut self, stmts: &[SNode]) -> Result<(), CompileError> {
        self.begin_scope();
        if stmts.is_empty() {
            self.chunk.emit(Op::Nil, self.line);
        } else {
            self.compile_block(stmts)?;
        }
        self.end_scope();
        Ok(())
    }

    fn compile_scoped_statements(&mut self, stmts: &[SNode]) -> Result<(), CompileError> {
        self.begin_scope();
        for sn in stmts {
            self.compile_node(sn)?;
            if Self::produces_value(&sn.node) {
                self.chunk.emit(Op::Pop, self.line);
            }
        }
        self.end_scope();
        Ok(())
    }

    fn compile_block(&mut self, stmts: &[SNode]) -> Result<(), CompileError> {
        for (i, snode) in stmts.iter().enumerate() {
            self.compile_node(snode)?;
            let is_last = i == stmts.len() - 1;
            if is_last {
                // Ensure the block always leaves exactly one value on the stack.
                if !Self::produces_value(&snode.node) {
                    self.chunk.emit(Op::Nil, self.line);
                }
            } else {
                if Self::produces_value(&snode.node) {
                    self.chunk.emit(Op::Pop, self.line);
                }
            }
        }
        Ok(())
    }

    fn compile_node(&mut self, snode: &SNode) -> Result<(), CompileError> {
        self.line = snode.span.line as u32;
        self.column = snode.span.column as u32;
        self.chunk.set_column(self.column);
        match &snode.node {
            Node::IntLiteral(n) => {
                let idx = self.chunk.add_constant(Constant::Int(*n));
                self.chunk.emit_u16(Op::Constant, idx, self.line);
            }
            Node::FloatLiteral(n) => {
                let idx = self.chunk.add_constant(Constant::Float(*n));
                self.chunk.emit_u16(Op::Constant, idx, self.line);
            }
            Node::StringLiteral(s) | Node::RawStringLiteral(s) => {
                let idx = self.chunk.add_constant(Constant::String(s.clone()));
                self.chunk.emit_u16(Op::Constant, idx, self.line);
            }
            Node::BoolLiteral(true) => self.chunk.emit(Op::True, self.line),
            Node::BoolLiteral(false) => self.chunk.emit(Op::False, self.line),
            Node::NilLiteral => self.chunk.emit(Op::Nil, self.line),
            Node::DurationLiteral(ms) => {
                let idx = self.chunk.add_constant(Constant::Duration(*ms));
                self.chunk.emit_u16(Op::Constant, idx, self.line);
            }

            Node::Identifier(name) => {
                let idx = self.chunk.add_constant(Constant::String(name.clone()));
                self.chunk.emit_u16(Op::GetVar, idx, self.line);
            }

            Node::LetBinding { pattern, value, .. } => {
                self.compile_node(value)?;
                self.compile_destructuring(pattern, false)?;
            }

            Node::VarBinding { pattern, value, .. } => {
                self.compile_node(value)?;
                self.compile_destructuring(pattern, true)?;
            }

            Node::Assignment {
                target, value, op, ..
            } => {
                if let Node::Identifier(name) = &target.node {
                    let idx = self.chunk.add_constant(Constant::String(name.clone()));
                    if let Some(op) = op {
                        self.chunk.emit_u16(Op::GetVar, idx, self.line);
                        self.compile_node(value)?;
                        self.emit_compound_op(op)?;
                        self.chunk.emit_u16(Op::SetVar, idx, self.line);
                    } else {
                        self.compile_node(value)?;
                        self.chunk.emit_u16(Op::SetVar, idx, self.line);
                    }
                } else if let Node::PropertyAccess { object, property } = &target.node {
                    if let Some(var_name) = self.root_var_name(object) {
                        let var_idx = self.chunk.add_constant(Constant::String(var_name.clone()));
                        let prop_idx = self.chunk.add_constant(Constant::String(property.clone()));
                        if let Some(op) = op {
                            self.compile_node(target)?;
                            self.compile_node(value)?;
                            self.emit_compound_op(op)?;
                        } else {
                            self.compile_node(value)?;
                        }
                        // SetProperty reads var_idx from env, sets prop, writes back.
                        // The variable name index is encoded as a second u16.
                        self.chunk.emit_u16(Op::SetProperty, prop_idx, self.line);
                        let hi = (var_idx >> 8) as u8;
                        let lo = var_idx as u8;
                        self.chunk.code.push(hi);
                        self.chunk.code.push(lo);
                        self.chunk.lines.push(self.line);
                        self.chunk.columns.push(self.column);
                        self.chunk.lines.push(self.line);
                        self.chunk.columns.push(self.column);
                    }
                } else if let Node::SubscriptAccess { object, index } = &target.node {
                    if let Some(var_name) = self.root_var_name(object) {
                        let var_idx = self.chunk.add_constant(Constant::String(var_name.clone()));
                        if let Some(op) = op {
                            self.compile_node(target)?;
                            self.compile_node(value)?;
                            self.emit_compound_op(op)?;
                        } else {
                            self.compile_node(value)?;
                        }
                        self.compile_node(index)?;
                        self.chunk.emit_u16(Op::SetSubscript, var_idx, self.line);
                    }
                }
            }

            Node::BinaryOp { op, left, right } => {
                match op.as_str() {
                    "&&" => {
                        self.compile_node(left)?;
                        let jump = self.chunk.emit_jump(Op::JumpIfFalse, self.line);
                        self.chunk.emit(Op::Pop, self.line);
                        self.compile_node(right)?;
                        self.chunk.patch_jump(jump);
                        // Normalize to bool.
                        self.chunk.emit(Op::Not, self.line);
                        self.chunk.emit(Op::Not, self.line);
                        return Ok(());
                    }
                    "||" => {
                        self.compile_node(left)?;
                        let jump = self.chunk.emit_jump(Op::JumpIfTrue, self.line);
                        self.chunk.emit(Op::Pop, self.line);
                        self.compile_node(right)?;
                        self.chunk.patch_jump(jump);
                        self.chunk.emit(Op::Not, self.line);
                        self.chunk.emit(Op::Not, self.line);
                        return Ok(());
                    }
                    "??" => {
                        self.compile_node(left)?;
                        self.chunk.emit(Op::Dup, self.line);
                        self.chunk.emit(Op::Nil, self.line);
                        self.chunk.emit(Op::NotEqual, self.line);
                        let jump = self.chunk.emit_jump(Op::JumpIfTrue, self.line);
                        self.chunk.emit(Op::Pop, self.line);
                        self.chunk.emit(Op::Pop, self.line);
                        self.compile_node(right)?;
                        let end = self.chunk.emit_jump(Op::Jump, self.line);
                        self.chunk.patch_jump(jump);
                        self.chunk.emit(Op::Pop, self.line);
                        self.chunk.patch_jump(end);
                        return Ok(());
                    }
                    "|>" => {
                        self.compile_node(left)?;
                        // `value |> func(_, arg)` desugars to `value |> { __pipe -> func(__pipe, arg) }`.
                        if contains_pipe_placeholder(right) {
                            let replaced = replace_pipe_placeholder(right);
                            let closure_node = SNode::dummy(Node::Closure {
                                params: vec![TypedParam {
                                    name: "__pipe".into(),
                                    type_expr: None,
                                    default_value: None,
                                    rest: false,
                                }],
                                body: vec![replaced],
                                fn_syntax: false,
                            });
                            self.compile_node(&closure_node)?;
                        } else {
                            self.compile_node(right)?;
                        }
                        self.chunk.emit(Op::Pipe, self.line);
                        return Ok(());
                    }
                    _ => {}
                }

                self.compile_node(left)?;
                self.compile_node(right)?;
                match op.as_str() {
                    "+" => self.chunk.emit(Op::Add, self.line),
                    "-" => self.chunk.emit(Op::Sub, self.line),
                    "*" => self.chunk.emit(Op::Mul, self.line),
                    "/" => self.chunk.emit(Op::Div, self.line),
                    "%" => self.chunk.emit(Op::Mod, self.line),
                    "**" => self.chunk.emit(Op::Pow, self.line),
                    "==" => self.chunk.emit(Op::Equal, self.line),
                    "!=" => self.chunk.emit(Op::NotEqual, self.line),
                    "<" => self.chunk.emit(Op::Less, self.line),
                    ">" => self.chunk.emit(Op::Greater, self.line),
                    "<=" => self.chunk.emit(Op::LessEqual, self.line),
                    ">=" => self.chunk.emit(Op::GreaterEqual, self.line),
                    "in" => self.chunk.emit(Op::Contains, self.line),
                    "not_in" => {
                        self.chunk.emit(Op::Contains, self.line);
                        self.chunk.emit(Op::Not, self.line);
                    }
                    _ => {
                        return Err(CompileError {
                            message: format!("Unknown operator: {op}"),
                            line: self.line,
                        })
                    }
                }
            }

            Node::UnaryOp { op, operand } => {
                self.compile_node(operand)?;
                match op.as_str() {
                    "-" => self.chunk.emit(Op::Negate, self.line),
                    "!" => self.chunk.emit(Op::Not, self.line),
                    _ => {}
                }
            }

            Node::Ternary {
                condition,
                true_expr,
                false_expr,
            } => {
                self.compile_node(condition)?;
                let else_jump = self.chunk.emit_jump(Op::JumpIfFalse, self.line);
                self.chunk.emit(Op::Pop, self.line);
                self.compile_node(true_expr)?;
                let end_jump = self.chunk.emit_jump(Op::Jump, self.line);
                self.chunk.patch_jump(else_jump);
                self.chunk.emit(Op::Pop, self.line);
                self.compile_node(false_expr)?;
                self.chunk.patch_jump(end_jump);
            }

            Node::FunctionCall { name, args } => {
                let has_spread = args.iter().any(|a| matches!(&a.node, Node::Spread(_)));
                let name_idx = self.chunk.add_constant(Constant::String(name.clone()));
                self.chunk.emit_u16(Op::Constant, name_idx, self.line);

                if has_spread {
                    // Flush-and-concat pattern: build args into one list
                    // (same as ListLiteral with spreads).
                    self.chunk.emit_u16(Op::BuildList, 0, self.line);
                    let mut pending = 0u16;
                    for arg in args {
                        if let Node::Spread(inner) = &arg.node {
                            if pending > 0 {
                                self.chunk.emit_u16(Op::BuildList, pending, self.line);
                                self.chunk.emit(Op::Add, self.line);
                                pending = 0;
                            }
                            self.compile_node(inner)?;
                            self.chunk.emit(Op::Dup, self.line);
                            let assert_idx = self
                                .chunk
                                .add_constant(Constant::String("__assert_list".into()));
                            self.chunk.emit_u16(Op::Constant, assert_idx, self.line);
                            self.chunk.emit(Op::Swap, self.line);
                            self.chunk.emit_u8(Op::Call, 1, self.line);
                            self.chunk.emit(Op::Pop, self.line);
                            self.chunk.emit(Op::Add, self.line);
                        } else {
                            self.compile_node(arg)?;
                            pending += 1;
                        }
                    }
                    if pending > 0 {
                        self.chunk.emit_u16(Op::BuildList, pending, self.line);
                        self.chunk.emit(Op::Add, self.line);
                    }
                    self.chunk.emit(Op::CallSpread, self.line);
                } else {
                    for arg in args {
                        self.compile_node(arg)?;
                    }
                    self.chunk.emit_u8(Op::Call, args.len() as u8, self.line);
                }
            }

            Node::MethodCall {
                object,
                method,
                args,
            } => {
                // EnumName.Variant(args) desugars to BuildEnum.
                if let Node::Identifier(name) = &object.node {
                    if self.enum_names.contains(name) {
                        for arg in args {
                            self.compile_node(arg)?;
                        }
                        let enum_idx = self.chunk.add_constant(Constant::String(name.clone()));
                        let var_idx = self.chunk.add_constant(Constant::String(method.clone()));
                        self.chunk.emit_u16(Op::BuildEnum, enum_idx, self.line);
                        let hi = (var_idx >> 8) as u8;
                        let lo = var_idx as u8;
                        self.chunk.code.push(hi);
                        self.chunk.code.push(lo);
                        self.chunk.lines.push(self.line);
                        self.chunk.columns.push(self.column);
                        self.chunk.lines.push(self.line);
                        self.chunk.columns.push(self.column);
                        let fc = args.len() as u16;
                        let fhi = (fc >> 8) as u8;
                        let flo = fc as u8;
                        self.chunk.code.push(fhi);
                        self.chunk.code.push(flo);
                        self.chunk.lines.push(self.line);
                        self.chunk.columns.push(self.column);
                        self.chunk.lines.push(self.line);
                        self.chunk.columns.push(self.column);
                        return Ok(());
                    }
                }
                let has_spread = args.iter().any(|a| matches!(&a.node, Node::Spread(_)));
                self.compile_node(object)?;
                let name_idx = self.chunk.add_constant(Constant::String(method.clone()));
                if has_spread {
                    self.chunk.emit_u16(Op::BuildList, 0, self.line);
                    let mut pending = 0u16;
                    for arg in args {
                        if let Node::Spread(inner) = &arg.node {
                            if pending > 0 {
                                self.chunk.emit_u16(Op::BuildList, pending, self.line);
                                self.chunk.emit(Op::Add, self.line);
                                pending = 0;
                            }
                            self.compile_node(inner)?;
                            self.chunk.emit(Op::Dup, self.line);
                            let assert_idx = self
                                .chunk
                                .add_constant(Constant::String("__assert_list".into()));
                            self.chunk.emit_u16(Op::Constant, assert_idx, self.line);
                            self.chunk.emit(Op::Swap, self.line);
                            self.chunk.emit_u8(Op::Call, 1, self.line);
                            self.chunk.emit(Op::Pop, self.line);
                            self.chunk.emit(Op::Add, self.line);
                        } else {
                            self.compile_node(arg)?;
                            pending += 1;
                        }
                    }
                    if pending > 0 {
                        self.chunk.emit_u16(Op::BuildList, pending, self.line);
                        self.chunk.emit(Op::Add, self.line);
                    }
                    self.chunk
                        .emit_u16(Op::MethodCallSpread, name_idx, self.line);
                } else {
                    for arg in args {
                        self.compile_node(arg)?;
                    }
                    self.chunk
                        .emit_method_call(name_idx, args.len() as u8, self.line);
                }
            }

            Node::OptionalMethodCall {
                object,
                method,
                args,
            } => {
                self.compile_node(object)?;
                for arg in args {
                    self.compile_node(arg)?;
                }
                let name_idx = self.chunk.add_constant(Constant::String(method.clone()));
                self.chunk
                    .emit_method_call_opt(name_idx, args.len() as u8, self.line);
            }

            Node::PropertyAccess { object, property } => {
                // Bare `EnumName.Variant` desugars to a zero-field BuildEnum.
                if let Node::Identifier(name) = &object.node {
                    if self.enum_names.contains(name) {
                        let enum_idx = self.chunk.add_constant(Constant::String(name.clone()));
                        let var_idx = self.chunk.add_constant(Constant::String(property.clone()));
                        self.chunk.emit_u16(Op::BuildEnum, enum_idx, self.line);
                        let hi = (var_idx >> 8) as u8;
                        let lo = var_idx as u8;
                        self.chunk.code.push(hi);
                        self.chunk.code.push(lo);
                        self.chunk.lines.push(self.line);
                        self.chunk.columns.push(self.column);
                        self.chunk.lines.push(self.line);
                        self.chunk.columns.push(self.column);
                        self.chunk.code.push(0);
                        self.chunk.code.push(0);
                        self.chunk.lines.push(self.line);
                        self.chunk.columns.push(self.column);
                        self.chunk.lines.push(self.line);
                        self.chunk.columns.push(self.column);
                        return Ok(());
                    }
                }
                self.compile_node(object)?;
                let idx = self.chunk.add_constant(Constant::String(property.clone()));
                self.chunk.emit_u16(Op::GetProperty, idx, self.line);
            }

            Node::OptionalPropertyAccess { object, property } => {
                self.compile_node(object)?;
                let idx = self.chunk.add_constant(Constant::String(property.clone()));
                self.chunk.emit_u16(Op::GetPropertyOpt, idx, self.line);
            }

            Node::SubscriptAccess { object, index } => {
                self.compile_node(object)?;
                self.compile_node(index)?;
                self.chunk.emit(Op::Subscript, self.line);
            }

            Node::SliceAccess { object, start, end } => {
                self.compile_node(object)?;
                if let Some(s) = start {
                    self.compile_node(s)?;
                } else {
                    self.chunk.emit(Op::Nil, self.line);
                }
                if let Some(e) = end {
                    self.compile_node(e)?;
                } else {
                    self.chunk.emit(Op::Nil, self.line);
                }
                self.chunk.emit(Op::Slice, self.line);
            }

            Node::IfElse {
                condition,
                then_body,
                else_body,
            } => {
                self.compile_node(condition)?;
                let else_jump = self.chunk.emit_jump(Op::JumpIfFalse, self.line);
                self.chunk.emit(Op::Pop, self.line);
                self.compile_scoped_block(then_body)?;
                if let Some(else_body) = else_body {
                    let end_jump = self.chunk.emit_jump(Op::Jump, self.line);
                    self.chunk.patch_jump(else_jump);
                    self.chunk.emit(Op::Pop, self.line);
                    self.compile_scoped_block(else_body)?;
                    self.chunk.patch_jump(end_jump);
                } else {
                    self.chunk.patch_jump(else_jump);
                    self.chunk.emit(Op::Pop, self.line);
                    self.chunk.emit(Op::Nil, self.line);
                }
            }

            Node::WhileLoop { condition, body } => {
                let loop_start = self.chunk.current_offset();
                self.loop_stack.push(LoopContext {
                    start_offset: loop_start,
                    break_patches: Vec::new(),
                    has_iterator: false,
                    handler_depth: self.handler_depth,
                    finally_depth: self.finally_bodies.len(),
                    scope_depth: self.scope_depth,
                });
                self.compile_node(condition)?;
                let exit_jump = self.chunk.emit_jump(Op::JumpIfFalse, self.line);
                self.chunk.emit(Op::Pop, self.line);
                self.compile_scoped_statements(body)?;
                // Jump back to condition
                self.chunk.emit_u16(Op::Jump, loop_start as u16, self.line);
                self.chunk.patch_jump(exit_jump);
                self.chunk.emit(Op::Pop, self.line);
                let ctx = self.loop_stack.pop().unwrap();
                for patch_pos in ctx.break_patches {
                    self.chunk.patch_jump(patch_pos);
                }
                self.chunk.emit(Op::Nil, self.line);
            }

            Node::ForIn {
                pattern,
                iterable,
                body,
            } => {
                self.compile_node(iterable)?;
                self.chunk.emit(Op::IterInit, self.line);
                let loop_start = self.chunk.current_offset();
                self.loop_stack.push(LoopContext {
                    start_offset: loop_start,
                    break_patches: Vec::new(),
                    has_iterator: true,
                    handler_depth: self.handler_depth,
                    finally_depth: self.finally_bodies.len(),
                    scope_depth: self.scope_depth,
                });
                // IterNext jumps to end if exhausted, else pushes the next item.
                let exit_jump_pos = self.chunk.emit_jump(Op::IterNext, self.line);
                self.begin_scope();
                self.compile_destructuring(pattern, true)?;
                for sn in body {
                    self.compile_node(sn)?;
                    if Self::produces_value(&sn.node) {
                        self.chunk.emit(Op::Pop, self.line);
                    }
                }
                self.end_scope();
                self.chunk.emit_u16(Op::Jump, loop_start as u16, self.line);
                self.chunk.patch_jump(exit_jump_pos);
                let ctx = self.loop_stack.pop().unwrap();
                for patch_pos in ctx.break_patches {
                    self.chunk.patch_jump(patch_pos);
                }
                self.chunk.emit(Op::Nil, self.line);
            }

            Node::ReturnStmt { value } => {
                if self.has_pending_finally() {
                    // Inside try-finally: save value to a temp, run pending
                    // finallys, then restore and return.
                    if let Some(val) = value {
                        self.compile_node(val)?;
                    } else {
                        self.chunk.emit(Op::Nil, self.line);
                    }
                    self.temp_counter += 1;
                    let temp_name = format!("__return_val_{}__", self.temp_counter);
                    let save_idx = self.chunk.add_constant(Constant::String(temp_name.clone()));
                    self.chunk.emit_u16(Op::DefVar, save_idx, self.line);
                    // Innermost finally first; skip catch barriers since
                    // return transfers past local handlers.
                    for fb in self.all_pending_finallys() {
                        self.compile_finally_inline(&fb)?;
                    }
                    let restore_idx = self.chunk.add_constant(Constant::String(temp_name));
                    self.chunk.emit_u16(Op::GetVar, restore_idx, self.line);
                    self.chunk.emit(Op::Return, self.line);
                } else {
                    // No pending finally — use tail-call optimization when possible.
                    if let Some(val) = value {
                        if let Node::FunctionCall { name, args } = &val.node {
                            let name_idx = self.chunk.add_constant(Constant::String(name.clone()));
                            self.chunk.emit_u16(Op::Constant, name_idx, self.line);
                            for arg in args {
                                self.compile_node(arg)?;
                            }
                            self.chunk
                                .emit_u8(Op::TailCall, args.len() as u8, self.line);
                        } else if let Node::BinaryOp { op, left, right } = &val.node {
                            if op == "|>" {
                                self.compile_node(left)?;
                                self.compile_node(right)?;
                                self.chunk.emit(Op::Swap, self.line);
                                self.chunk.emit_u8(Op::TailCall, 1, self.line);
                            } else {
                                self.compile_node(val)?;
                            }
                        } else {
                            self.compile_node(val)?;
                        }
                    } else {
                        self.chunk.emit(Op::Nil, self.line);
                    }
                    self.chunk.emit(Op::Return, self.line);
                }
            }

            Node::BreakStmt => {
                if self.loop_stack.is_empty() {
                    return Err(CompileError {
                        message: "break outside of loop".to_string(),
                        line: self.line,
                    });
                }
                // Copy values out to avoid borrow conflict.
                let ctx = self.loop_stack.last().unwrap();
                let finally_depth = ctx.finally_depth;
                let handler_depth = ctx.handler_depth;
                let has_iterator = ctx.has_iterator;
                let scope_depth = ctx.scope_depth;
                for _ in handler_depth..self.handler_depth {
                    self.chunk.emit(Op::PopHandler, self.line);
                }
                for fb in self.pending_finallys_down_to(finally_depth) {
                    self.compile_finally_inline(&fb)?;
                }
                self.unwind_scopes_to(scope_depth);
                if has_iterator {
                    self.chunk.emit(Op::PopIterator, self.line);
                }
                let patch = self.chunk.emit_jump(Op::Jump, self.line);
                self.loop_stack
                    .last_mut()
                    .unwrap()
                    .break_patches
                    .push(patch);
            }

            Node::ContinueStmt => {
                if self.loop_stack.is_empty() {
                    return Err(CompileError {
                        message: "continue outside of loop".to_string(),
                        line: self.line,
                    });
                }
                let ctx = self.loop_stack.last().unwrap();
                let finally_depth = ctx.finally_depth;
                let handler_depth = ctx.handler_depth;
                let loop_start = ctx.start_offset;
                let scope_depth = ctx.scope_depth;
                for _ in handler_depth..self.handler_depth {
                    self.chunk.emit(Op::PopHandler, self.line);
                }
                for fb in self.pending_finallys_down_to(finally_depth) {
                    self.compile_finally_inline(&fb)?;
                }
                self.unwind_scopes_to(scope_depth);
                self.chunk.emit_u16(Op::Jump, loop_start as u16, self.line);
            }

            Node::ListLiteral(elements) => {
                let has_spread = elements.iter().any(|e| matches!(&e.node, Node::Spread(_)));
                if !has_spread {
                    for el in elements {
                        self.compile_node(el)?;
                    }
                    self.chunk
                        .emit_u16(Op::BuildList, elements.len() as u16, self.line);
                } else {
                    // Flush-and-concat: accumulate non-spread elements and concat with spread lists.
                    self.chunk.emit_u16(Op::BuildList, 0, self.line);
                    let mut pending = 0u16;
                    for el in elements {
                        if let Node::Spread(inner) = &el.node {
                            if pending > 0 {
                                self.chunk.emit_u16(Op::BuildList, pending, self.line);
                                self.chunk.emit(Op::Add, self.line);
                                pending = 0;
                            }
                            self.compile_node(inner)?;
                            self.chunk.emit(Op::Dup, self.line);
                            let assert_idx = self
                                .chunk
                                .add_constant(Constant::String("__assert_list".into()));
                            self.chunk.emit_u16(Op::Constant, assert_idx, self.line);
                            self.chunk.emit(Op::Swap, self.line);
                            self.chunk.emit_u8(Op::Call, 1, self.line);
                            self.chunk.emit(Op::Pop, self.line);
                            self.chunk.emit(Op::Add, self.line);
                        } else {
                            self.compile_node(el)?;
                            pending += 1;
                        }
                    }
                    if pending > 0 {
                        self.chunk.emit_u16(Op::BuildList, pending, self.line);
                        self.chunk.emit(Op::Add, self.line);
                    }
                }
            }

            Node::DictLiteral(entries) => {
                let has_spread = entries
                    .iter()
                    .any(|e| matches!(&e.value.node, Node::Spread(_)));
                if !has_spread {
                    for entry in entries {
                        self.compile_node(&entry.key)?;
                        self.compile_node(&entry.value)?;
                    }
                    self.chunk
                        .emit_u16(Op::BuildDict, entries.len() as u16, self.line);
                } else {
                    // Flush-and-merge via Add on empty dict.
                    self.chunk.emit_u16(Op::BuildDict, 0, self.line);
                    let mut pending = 0u16;
                    for entry in entries {
                        if let Node::Spread(inner) = &entry.value.node {
                            if pending > 0 {
                                self.chunk.emit_u16(Op::BuildDict, pending, self.line);
                                self.chunk.emit(Op::Add, self.line);
                                pending = 0;
                            }
                            self.compile_node(inner)?;
                            self.chunk.emit(Op::Dup, self.line);
                            let assert_idx = self
                                .chunk
                                .add_constant(Constant::String("__assert_dict".into()));
                            self.chunk.emit_u16(Op::Constant, assert_idx, self.line);
                            self.chunk.emit(Op::Swap, self.line);
                            self.chunk.emit_u8(Op::Call, 1, self.line);
                            self.chunk.emit(Op::Pop, self.line);
                            self.chunk.emit(Op::Add, self.line);
                        } else {
                            self.compile_node(&entry.key)?;
                            self.compile_node(&entry.value)?;
                            pending += 1;
                        }
                    }
                    if pending > 0 {
                        self.chunk.emit_u16(Op::BuildDict, pending, self.line);
                        self.chunk.emit(Op::Add, self.line);
                    }
                }
            }

            Node::InterpolatedString(segments) => {
                let mut part_count = 0u16;
                for seg in segments {
                    match seg {
                        StringSegment::Literal(s) => {
                            let idx = self.chunk.add_constant(Constant::String(s.clone()));
                            self.chunk.emit_u16(Op::Constant, idx, self.line);
                            part_count += 1;
                        }
                        StringSegment::Expression(expr_str, expr_line, expr_col) => {
                            let mut lexer =
                                harn_lexer::Lexer::with_position(expr_str, *expr_line, *expr_col);
                            if let Ok(tokens) = lexer.tokenize() {
                                let mut parser = harn_parser::Parser::new(tokens);
                                if let Ok(snode) = parser.parse_single_expression() {
                                    self.compile_node(&snode)?;
                                    let to_str = self
                                        .chunk
                                        .add_constant(Constant::String("to_string".into()));
                                    self.chunk.emit_u16(Op::Constant, to_str, self.line);
                                    self.chunk.emit(Op::Swap, self.line);
                                    self.chunk.emit_u8(Op::Call, 1, self.line);
                                    part_count += 1;
                                } else {
                                    // Fallback: treat as literal.
                                    let idx =
                                        self.chunk.add_constant(Constant::String(expr_str.clone()));
                                    self.chunk.emit_u16(Op::Constant, idx, self.line);
                                    part_count += 1;
                                }
                            }
                        }
                    }
                }
                if part_count > 1 {
                    self.chunk.emit_u16(Op::Concat, part_count, self.line);
                }
            }

            Node::FnDecl {
                name, params, body, ..
            } => {
                let mut fn_compiler = Compiler::new();
                fn_compiler.enum_names = self.enum_names.clone();
                fn_compiler.emit_default_preamble(params)?;
                fn_compiler.emit_type_checks(params);
                let is_gen = body_contains_yield(body);
                fn_compiler.compile_block(body)?;
                // Run pending defers before implicit return
                for fb in fn_compiler.all_pending_finallys() {
                    fn_compiler.compile_finally_inline(&fb)?;
                }
                fn_compiler.chunk.emit(Op::Nil, self.line);
                fn_compiler.chunk.emit(Op::Return, self.line);

                let func = CompiledFunction {
                    name: name.clone(),
                    params: TypedParam::names(params),
                    default_start: TypedParam::default_start(params),
                    chunk: fn_compiler.chunk,
                    is_generator: is_gen,
                    has_rest_param: params.last().is_some_and(|p| p.rest),
                };
                let fn_idx = self.chunk.functions.len();
                self.chunk.functions.push(func);

                self.chunk.emit_u16(Op::Closure, fn_idx as u16, self.line);
                let name_idx = self.chunk.add_constant(Constant::String(name.clone()));
                self.chunk.emit_u16(Op::DefLet, name_idx, self.line);
            }

            Node::ToolDecl {
                name,
                description,
                params,
                return_type,
                body,
                ..
            } => {
                // Compile the body as a closure, then call `tool_define(registry, name, description, config)`.
                let mut fn_compiler = Compiler::new();
                fn_compiler.enum_names = self.enum_names.clone();
                fn_compiler.emit_default_preamble(params)?;
                fn_compiler.emit_type_checks(params);
                fn_compiler.compile_block(body)?;
                // Run pending defers before implicit return
                for fb in fn_compiler.all_pending_finallys() {
                    fn_compiler.compile_finally_inline(&fb)?;
                }
                fn_compiler.chunk.emit(Op::Return, self.line);

                let func = CompiledFunction {
                    name: name.clone(),
                    params: TypedParam::names(params),
                    default_start: TypedParam::default_start(params),
                    chunk: fn_compiler.chunk,
                    is_generator: false,
                    has_rest_param: params.last().is_some_and(|p| p.rest),
                };
                let fn_idx = self.chunk.functions.len();
                self.chunk.functions.push(func);

                let define_name = self
                    .chunk
                    .add_constant(Constant::String("tool_define".into()));
                self.chunk.emit_u16(Op::Constant, define_name, self.line);

                let reg_name = self
                    .chunk
                    .add_constant(Constant::String("tool_registry".into()));
                self.chunk.emit_u16(Op::Constant, reg_name, self.line);
                self.chunk.emit_u8(Op::Call, 0, self.line);

                let tool_name_idx = self.chunk.add_constant(Constant::String(name.clone()));
                self.chunk.emit_u16(Op::Constant, tool_name_idx, self.line);

                let desc = description.as_deref().unwrap_or("");
                let desc_idx = self.chunk.add_constant(Constant::String(desc.to_string()));
                self.chunk.emit_u16(Op::Constant, desc_idx, self.line);

                // Build parameters dict using the same schema lowering as
                // runtime param validation so tools expose nested shapes,
                // unions, item schemas, defaults, and dict value schemas.
                let mut param_count: u16 = 0;
                for p in params {
                    let pn_idx = self.chunk.add_constant(Constant::String(p.name.clone()));
                    self.chunk.emit_u16(Op::Constant, pn_idx, self.line);

                    let base_schema = p
                        .type_expr
                        .as_ref()
                        .and_then(Self::type_expr_to_schema_value)
                        .unwrap_or_else(|| {
                            VmValue::Dict(Rc::new(BTreeMap::from([(
                                "type".to_string(),
                                VmValue::String(Rc::from("any")),
                            )])))
                        });
                    let public_schema =
                        schema::schema_to_json_schema_value(&base_schema).map_err(|error| {
                            CompileError {
                                message: format!(
                                    "failed to lower tool parameter schema for '{}': {}",
                                    p.name, error
                                ),
                                line: self.line,
                            }
                        })?;
                    let mut param_schema = match public_schema {
                        VmValue::Dict(map) => (*map).clone(),
                        _ => BTreeMap::new(),
                    };

                    if p.default_value.is_some() {
                        param_schema.insert("required".to_string(), VmValue::Bool(false));
                    }

                    self.emit_vm_value_literal(&VmValue::Dict(Rc::new(param_schema)));

                    if let Some(default_value) = p.default_value.as_ref() {
                        let default_key =
                            self.chunk.add_constant(Constant::String("default".into()));
                        self.chunk.emit_u16(Op::Constant, default_key, self.line);
                        self.compile_node(default_value)?;
                        self.chunk.emit_u16(Op::BuildDict, 1, self.line);
                        self.chunk.emit(Op::Add, self.line);
                    }

                    param_count += 1;
                }
                self.chunk.emit_u16(Op::BuildDict, param_count, self.line);

                let params_key = self
                    .chunk
                    .add_constant(Constant::String("parameters".into()));
                self.chunk.emit_u16(Op::Constant, params_key, self.line);
                self.chunk.emit(Op::Swap, self.line);

                let handler_key = self.chunk.add_constant(Constant::String("handler".into()));
                self.chunk.emit_u16(Op::Constant, handler_key, self.line);
                self.chunk.emit_u16(Op::Closure, fn_idx as u16, self.line);

                let mut config_entries = 2u16;
                if let Some(return_type) = return_type
                    .as_ref()
                    .and_then(Self::type_expr_to_schema_value)
                {
                    let return_type =
                        schema::schema_to_json_schema_value(&return_type).map_err(|error| {
                            CompileError {
                                message: format!(
                                    "failed to lower tool return schema for '{}': {}",
                                    name, error
                                ),
                                line: self.line,
                            }
                        })?;
                    let returns_key = self.chunk.add_constant(Constant::String("returns".into()));
                    self.chunk.emit_u16(Op::Constant, returns_key, self.line);
                    self.emit_vm_value_literal(&return_type);
                    config_entries += 1;
                }

                self.chunk
                    .emit_u16(Op::BuildDict, config_entries, self.line);

                self.chunk.emit_u8(Op::Call, 4, self.line);

                let bind_idx = self.chunk.add_constant(Constant::String(name.clone()));
                self.chunk.emit_u16(Op::DefLet, bind_idx, self.line);
            }

            Node::Closure { params, body, .. } => {
                let mut fn_compiler = Compiler::new();
                fn_compiler.enum_names = self.enum_names.clone();
                fn_compiler.emit_default_preamble(params)?;
                fn_compiler.emit_type_checks(params);
                let is_gen = body_contains_yield(body);
                fn_compiler.compile_block(body)?;
                // Run pending defers before implicit return
                for fb in fn_compiler.all_pending_finallys() {
                    fn_compiler.compile_finally_inline(&fb)?;
                }
                fn_compiler.chunk.emit(Op::Return, self.line);

                let func = CompiledFunction {
                    name: "<closure>".to_string(),
                    params: TypedParam::names(params),
                    default_start: TypedParam::default_start(params),
                    chunk: fn_compiler.chunk,
                    is_generator: is_gen,
                    has_rest_param: false,
                };
                let fn_idx = self.chunk.functions.len();
                self.chunk.functions.push(func);

                self.chunk.emit_u16(Op::Closure, fn_idx as u16, self.line);
            }

            Node::ThrowStmt { value } => {
                // Only run finallys the unwind will actually cross — i.e.,
                // those between this throw and the innermost `CatchBarrier`.
                // Finallys beyond the nearest local `catch` aren't on the
                // throw's escape path (the catch halts unwinding there), so
                // pre-running them wrongly fires outer side effects.
                let pending = self.pending_finallys_until_barrier();
                if !pending.is_empty() {
                    self.compile_node(value)?;
                    self.temp_counter += 1;
                    let temp_name = format!("__throw_val_{}__", self.temp_counter);
                    let save_idx = self.chunk.add_constant(Constant::String(temp_name.clone()));
                    self.chunk.emit_u16(Op::DefVar, save_idx, self.line);
                    for fb in &pending {
                        self.compile_finally_inline(fb)?;
                    }
                    let restore_idx = self.chunk.add_constant(Constant::String(temp_name));
                    self.chunk.emit_u16(Op::GetVar, restore_idx, self.line);
                    self.chunk.emit(Op::Throw, self.line);
                } else {
                    self.compile_node(value)?;
                    self.chunk.emit(Op::Throw, self.line);
                }
            }

            Node::MatchExpr { value, arms } => {
                self.compile_node(value)?;
                let mut end_jumps = Vec::new();
                for arm in arms {
                    match &arm.pattern.node {
                        // Wildcard `_` — always matches (unless guarded)
                        Node::Identifier(name) if name == "_" => {
                            if let Some(ref guard) = arm.guard {
                                self.compile_node(guard)?;
                                let guard_skip = self.chunk.emit_jump(Op::JumpIfFalse, self.line);
                                self.chunk.emit(Op::Pop, self.line);
                                self.begin_scope();
                                self.chunk.emit(Op::Pop, self.line);
                                self.compile_match_body(&arm.body)?;
                                self.end_scope();
                                end_jumps.push(self.chunk.emit_jump(Op::Jump, self.line));
                                self.chunk.patch_jump(guard_skip);
                                self.chunk.emit(Op::Pop, self.line);
                            } else {
                                self.begin_scope();
                                self.chunk.emit(Op::Pop, self.line);
                                self.compile_match_body(&arm.body)?;
                                self.end_scope();
                                end_jumps.push(self.chunk.emit_jump(Op::Jump, self.line));
                            }
                        }
                        // Enum destructuring: EnumConstruct pattern
                        Node::EnumConstruct {
                            enum_name,
                            variant,
                            args: pat_args,
                        } => {
                            self.chunk.emit(Op::Dup, self.line);
                            let en_idx =
                                self.chunk.add_constant(Constant::String(enum_name.clone()));
                            let vn_idx = self.chunk.add_constant(Constant::String(variant.clone()));
                            self.chunk.emit_u16(Op::MatchEnum, en_idx, self.line);
                            let hi = (vn_idx >> 8) as u8;
                            let lo = vn_idx as u8;
                            self.chunk.code.push(hi);
                            self.chunk.code.push(lo);
                            self.chunk.lines.push(self.line);
                            self.chunk.columns.push(self.column);
                            self.chunk.lines.push(self.line);
                            self.chunk.columns.push(self.column);
                            let skip = self.chunk.emit_jump(Op::JumpIfFalse, self.line);
                            self.chunk.emit(Op::Pop, self.line);
                            self.begin_scope();

                            // Bind field variables from the enum's fields; the
                            // match value stays on the stack for extraction.
                            for (i, pat_arg) in pat_args.iter().enumerate() {
                                if let Node::Identifier(binding_name) = &pat_arg.node {
                                    self.chunk.emit(Op::Dup, self.line);
                                    let fields_idx = self
                                        .chunk
                                        .add_constant(Constant::String("fields".to_string()));
                                    self.chunk.emit_u16(Op::GetProperty, fields_idx, self.line);
                                    let idx_const =
                                        self.chunk.add_constant(Constant::Int(i as i64));
                                    self.chunk.emit_u16(Op::Constant, idx_const, self.line);
                                    self.chunk.emit(Op::Subscript, self.line);
                                    let name_idx = self
                                        .chunk
                                        .add_constant(Constant::String(binding_name.clone()));
                                    self.chunk.emit_u16(Op::DefLet, name_idx, self.line);
                                }
                            }

                            // Optional guard
                            if let Some(ref guard) = arm.guard {
                                self.compile_node(guard)?;
                                let guard_skip = self.chunk.emit_jump(Op::JumpIfFalse, self.line);
                                self.chunk.emit(Op::Pop, self.line);
                                self.chunk.emit(Op::Pop, self.line);
                                self.compile_match_body(&arm.body)?;
                                self.end_scope();
                                end_jumps.push(self.chunk.emit_jump(Op::Jump, self.line));
                                self.chunk.patch_jump(guard_skip);
                                self.chunk.emit(Op::Pop, self.line);
                                self.end_scope();
                            } else {
                                self.chunk.emit(Op::Pop, self.line);
                                self.compile_match_body(&arm.body)?;
                                self.end_scope();
                                end_jumps.push(self.chunk.emit_jump(Op::Jump, self.line));
                            }
                            self.chunk.patch_jump(skip);
                            self.chunk.emit(Op::Pop, self.line);
                        }
                        // Enum variant without args: PropertyAccess(EnumName, Variant)
                        Node::PropertyAccess { object, property } if matches!(&object.node, Node::Identifier(n) if self.enum_names.contains(n)) =>
                        {
                            let enum_name = if let Node::Identifier(n) = &object.node {
                                n.clone()
                            } else {
                                unreachable!()
                            };
                            self.chunk.emit(Op::Dup, self.line);
                            let en_idx = self.chunk.add_constant(Constant::String(enum_name));
                            let vn_idx =
                                self.chunk.add_constant(Constant::String(property.clone()));
                            self.chunk.emit_u16(Op::MatchEnum, en_idx, self.line);
                            let hi = (vn_idx >> 8) as u8;
                            let lo = vn_idx as u8;
                            self.chunk.code.push(hi);
                            self.chunk.code.push(lo);
                            self.chunk.lines.push(self.line);
                            self.chunk.columns.push(self.column);
                            self.chunk.lines.push(self.line);
                            self.chunk.columns.push(self.column);
                            let skip = self.chunk.emit_jump(Op::JumpIfFalse, self.line);
                            self.chunk.emit(Op::Pop, self.line);
                            // Optional guard
                            if let Some(ref guard) = arm.guard {
                                self.compile_node(guard)?;
                                let guard_skip = self.chunk.emit_jump(Op::JumpIfFalse, self.line);
                                self.chunk.emit(Op::Pop, self.line);
                                self.begin_scope();
                                self.chunk.emit(Op::Pop, self.line);
                                self.compile_match_body(&arm.body)?;
                                self.end_scope();
                                end_jumps.push(self.chunk.emit_jump(Op::Jump, self.line));
                                self.chunk.patch_jump(guard_skip);
                                self.chunk.emit(Op::Pop, self.line);
                            } else {
                                self.begin_scope();
                                self.chunk.emit(Op::Pop, self.line);
                                self.compile_match_body(&arm.body)?;
                                self.end_scope();
                                end_jumps.push(self.chunk.emit_jump(Op::Jump, self.line));
                            }
                            self.chunk.patch_jump(skip);
                            self.chunk.emit(Op::Pop, self.line);
                        }
                        // Enum destructuring via MethodCall: EnumName.Variant(bindings...)
                        // Parser produces MethodCall for EnumName.Variant(x) patterns
                        Node::MethodCall {
                            object,
                            method,
                            args: pat_args,
                        } if matches!(&object.node, Node::Identifier(n) if self.enum_names.contains(n)) =>
                        {
                            let enum_name = if let Node::Identifier(n) = &object.node {
                                n.clone()
                            } else {
                                unreachable!()
                            };
                            self.chunk.emit(Op::Dup, self.line);
                            let en_idx = self.chunk.add_constant(Constant::String(enum_name));
                            let vn_idx = self.chunk.add_constant(Constant::String(method.clone()));
                            self.chunk.emit_u16(Op::MatchEnum, en_idx, self.line);
                            let hi = (vn_idx >> 8) as u8;
                            let lo = vn_idx as u8;
                            self.chunk.code.push(hi);
                            self.chunk.code.push(lo);
                            self.chunk.lines.push(self.line);
                            self.chunk.columns.push(self.column);
                            self.chunk.lines.push(self.line);
                            self.chunk.columns.push(self.column);
                            let skip = self.chunk.emit_jump(Op::JumpIfFalse, self.line);
                            self.chunk.emit(Op::Pop, self.line);
                            self.begin_scope();

                            for (i, pat_arg) in pat_args.iter().enumerate() {
                                if let Node::Identifier(binding_name) = &pat_arg.node {
                                    self.chunk.emit(Op::Dup, self.line);
                                    let fields_idx = self
                                        .chunk
                                        .add_constant(Constant::String("fields".to_string()));
                                    self.chunk.emit_u16(Op::GetProperty, fields_idx, self.line);
                                    let idx_const =
                                        self.chunk.add_constant(Constant::Int(i as i64));
                                    self.chunk.emit_u16(Op::Constant, idx_const, self.line);
                                    self.chunk.emit(Op::Subscript, self.line);
                                    let name_idx = self
                                        .chunk
                                        .add_constant(Constant::String(binding_name.clone()));
                                    self.chunk.emit_u16(Op::DefLet, name_idx, self.line);
                                }
                            }

                            // Optional guard
                            if let Some(ref guard) = arm.guard {
                                self.compile_node(guard)?;
                                let guard_skip = self.chunk.emit_jump(Op::JumpIfFalse, self.line);
                                self.chunk.emit(Op::Pop, self.line);
                                self.chunk.emit(Op::Pop, self.line);
                                self.compile_match_body(&arm.body)?;
                                self.end_scope();
                                end_jumps.push(self.chunk.emit_jump(Op::Jump, self.line));
                                self.chunk.patch_jump(guard_skip);
                                self.chunk.emit(Op::Pop, self.line);
                                self.end_scope();
                            } else {
                                self.chunk.emit(Op::Pop, self.line);
                                self.compile_match_body(&arm.body)?;
                                self.end_scope();
                                end_jumps.push(self.chunk.emit_jump(Op::Jump, self.line));
                            }
                            self.chunk.patch_jump(skip);
                            self.chunk.emit(Op::Pop, self.line);
                        }
                        // Binding pattern: bare identifier always matches.
                        Node::Identifier(name) => {
                            self.begin_scope();
                            self.chunk.emit(Op::Dup, self.line);
                            let name_idx = self.chunk.add_constant(Constant::String(name.clone()));
                            self.chunk.emit_u16(Op::DefLet, name_idx, self.line);
                            // Optional guard
                            if let Some(ref guard) = arm.guard {
                                self.compile_node(guard)?;
                                let guard_skip = self.chunk.emit_jump(Op::JumpIfFalse, self.line);
                                self.chunk.emit(Op::Pop, self.line);
                                self.chunk.emit(Op::Pop, self.line);
                                self.compile_match_body(&arm.body)?;
                                self.end_scope();
                                end_jumps.push(self.chunk.emit_jump(Op::Jump, self.line));
                                self.chunk.patch_jump(guard_skip);
                                self.chunk.emit(Op::Pop, self.line);
                                self.end_scope();
                            } else {
                                self.chunk.emit(Op::Pop, self.line);
                                self.compile_match_body(&arm.body)?;
                                self.end_scope();
                                end_jumps.push(self.chunk.emit_jump(Op::Jump, self.line));
                            }
                        }
                        // Dict pattern: {key: literal, key: binding, ...}
                        Node::DictLiteral(entries)
                            if entries
                                .iter()
                                .all(|e| matches!(&e.key.node, Node::StringLiteral(_))) =>
                        {
                            self.chunk.emit(Op::Dup, self.line);
                            let typeof_idx =
                                self.chunk.add_constant(Constant::String("type_of".into()));
                            self.chunk.emit_u16(Op::Constant, typeof_idx, self.line);
                            self.chunk.emit(Op::Swap, self.line);
                            self.chunk.emit_u8(Op::Call, 1, self.line);
                            let dict_str = self.chunk.add_constant(Constant::String("dict".into()));
                            self.chunk.emit_u16(Op::Constant, dict_str, self.line);
                            self.chunk.emit(Op::Equal, self.line);
                            let skip_type = self.chunk.emit_jump(Op::JumpIfFalse, self.line);
                            self.chunk.emit(Op::Pop, self.line);

                            let mut constraint_skips = Vec::new();
                            let mut bindings = Vec::new();
                            self.begin_scope();
                            for entry in entries {
                                if let Node::StringLiteral(key) = &entry.key.node {
                                    match &entry.value.node {
                                        Node::StringLiteral(_)
                                        | Node::IntLiteral(_)
                                        | Node::FloatLiteral(_)
                                        | Node::BoolLiteral(_)
                                        | Node::NilLiteral => {
                                            self.chunk.emit(Op::Dup, self.line);
                                            let key_idx = self
                                                .chunk
                                                .add_constant(Constant::String(key.clone()));
                                            self.chunk.emit_u16(Op::Constant, key_idx, self.line);
                                            self.chunk.emit(Op::Subscript, self.line);
                                            self.compile_node(&entry.value)?;
                                            self.chunk.emit(Op::Equal, self.line);
                                            let skip =
                                                self.chunk.emit_jump(Op::JumpIfFalse, self.line);
                                            self.chunk.emit(Op::Pop, self.line);
                                            constraint_skips.push(skip);
                                        }
                                        Node::Identifier(binding) => {
                                            bindings.push((key.clone(), binding.clone()));
                                        }
                                        _ => {
                                            // Complex expression constraint: dict[key] == expr.
                                            self.chunk.emit(Op::Dup, self.line);
                                            let key_idx = self
                                                .chunk
                                                .add_constant(Constant::String(key.clone()));
                                            self.chunk.emit_u16(Op::Constant, key_idx, self.line);
                                            self.chunk.emit(Op::Subscript, self.line);
                                            self.compile_node(&entry.value)?;
                                            self.chunk.emit(Op::Equal, self.line);
                                            let skip =
                                                self.chunk.emit_jump(Op::JumpIfFalse, self.line);
                                            self.chunk.emit(Op::Pop, self.line);
                                            constraint_skips.push(skip);
                                        }
                                    }
                                }
                            }

                            for (key, binding) in &bindings {
                                self.chunk.emit(Op::Dup, self.line);
                                let key_idx =
                                    self.chunk.add_constant(Constant::String(key.clone()));
                                self.chunk.emit_u16(Op::Constant, key_idx, self.line);
                                self.chunk.emit(Op::Subscript, self.line);
                                let name_idx =
                                    self.chunk.add_constant(Constant::String(binding.clone()));
                                self.chunk.emit_u16(Op::DefLet, name_idx, self.line);
                            }

                            // Optional guard
                            if let Some(ref guard) = arm.guard {
                                self.compile_node(guard)?;
                                let guard_skip = self.chunk.emit_jump(Op::JumpIfFalse, self.line);
                                self.chunk.emit(Op::Pop, self.line);
                                self.chunk.emit(Op::Pop, self.line);
                                self.compile_match_body(&arm.body)?;
                                self.end_scope();
                                end_jumps.push(self.chunk.emit_jump(Op::Jump, self.line));
                                self.chunk.patch_jump(guard_skip);
                                // Guard failed: pop guard bool, fall through to scope cleanup below.
                                self.chunk.emit(Op::Pop, self.line);
                            } else {
                                self.chunk.emit(Op::Pop, self.line);
                                self.compile_match_body(&arm.body)?;
                                self.end_scope();
                                end_jumps.push(self.chunk.emit_jump(Op::Jump, self.line));
                            }

                            let type_fail_target = self.chunk.code.len();
                            self.chunk.emit(Op::Pop, self.line);
                            let next_arm_jump = self.chunk.emit_jump(Op::Jump, self.line);
                            let scoped_fail_target = self.chunk.code.len();
                            self.chunk.emit(Op::PopScope, self.line);
                            self.chunk.emit(Op::Pop, self.line);
                            let next_arm_target = self.chunk.code.len();

                            for skip in constraint_skips {
                                self.chunk.patch_jump_to(skip, scoped_fail_target);
                            }
                            self.chunk.patch_jump_to(skip_type, type_fail_target);
                            self.chunk.patch_jump_to(next_arm_jump, next_arm_target);
                        }
                        // List pattern: [literal, binding, ...]
                        Node::ListLiteral(elements) => {
                            self.chunk.emit(Op::Dup, self.line);
                            let typeof_idx =
                                self.chunk.add_constant(Constant::String("type_of".into()));
                            self.chunk.emit_u16(Op::Constant, typeof_idx, self.line);
                            self.chunk.emit(Op::Swap, self.line);
                            self.chunk.emit_u8(Op::Call, 1, self.line);
                            let list_str = self.chunk.add_constant(Constant::String("list".into()));
                            self.chunk.emit_u16(Op::Constant, list_str, self.line);
                            self.chunk.emit(Op::Equal, self.line);
                            let skip_type = self.chunk.emit_jump(Op::JumpIfFalse, self.line);
                            self.chunk.emit(Op::Pop, self.line);

                            self.chunk.emit(Op::Dup, self.line);
                            let len_idx = self.chunk.add_constant(Constant::String("len".into()));
                            self.chunk.emit_u16(Op::Constant, len_idx, self.line);
                            self.chunk.emit(Op::Swap, self.line);
                            self.chunk.emit_u8(Op::Call, 1, self.line);
                            let count = self
                                .chunk
                                .add_constant(Constant::Int(elements.len() as i64));
                            self.chunk.emit_u16(Op::Constant, count, self.line);
                            self.chunk.emit(Op::GreaterEqual, self.line);
                            let skip_len = self.chunk.emit_jump(Op::JumpIfFalse, self.line);
                            self.chunk.emit(Op::Pop, self.line);

                            let mut constraint_skips = Vec::new();
                            let mut bindings = Vec::new();
                            self.begin_scope();
                            for (i, elem) in elements.iter().enumerate() {
                                match &elem.node {
                                    Node::Identifier(name) if name != "_" => {
                                        bindings.push((i, name.clone()));
                                    }
                                    Node::Identifier(_) => {} // wildcard `_`
                                    _ => {
                                        self.chunk.emit(Op::Dup, self.line);
                                        let idx_const =
                                            self.chunk.add_constant(Constant::Int(i as i64));
                                        self.chunk.emit_u16(Op::Constant, idx_const, self.line);
                                        self.chunk.emit(Op::Subscript, self.line);
                                        self.compile_node(elem)?;
                                        self.chunk.emit(Op::Equal, self.line);
                                        let skip = self.chunk.emit_jump(Op::JumpIfFalse, self.line);
                                        self.chunk.emit(Op::Pop, self.line);
                                        constraint_skips.push(skip);
                                    }
                                }
                            }

                            for (i, name) in &bindings {
                                self.chunk.emit(Op::Dup, self.line);
                                let idx_const = self.chunk.add_constant(Constant::Int(*i as i64));
                                self.chunk.emit_u16(Op::Constant, idx_const, self.line);
                                self.chunk.emit(Op::Subscript, self.line);
                                let name_idx =
                                    self.chunk.add_constant(Constant::String(name.clone()));
                                self.chunk.emit_u16(Op::DefLet, name_idx, self.line);
                            }

                            // Optional guard
                            if let Some(ref guard) = arm.guard {
                                self.compile_node(guard)?;
                                let guard_skip = self.chunk.emit_jump(Op::JumpIfFalse, self.line);
                                self.chunk.emit(Op::Pop, self.line);
                                self.chunk.emit(Op::Pop, self.line);
                                self.compile_match_body(&arm.body)?;
                                self.end_scope();
                                end_jumps.push(self.chunk.emit_jump(Op::Jump, self.line));
                                self.chunk.patch_jump(guard_skip);
                                self.chunk.emit(Op::Pop, self.line);
                            } else {
                                self.chunk.emit(Op::Pop, self.line);
                                self.compile_match_body(&arm.body)?;
                                self.end_scope();
                                end_jumps.push(self.chunk.emit_jump(Op::Jump, self.line));
                            }

                            let pre_scope_fail_target = self.chunk.code.len();
                            self.chunk.emit(Op::Pop, self.line);
                            let next_arm_jump = self.chunk.emit_jump(Op::Jump, self.line);
                            let scoped_fail_target = self.chunk.code.len();
                            self.chunk.emit(Op::PopScope, self.line);
                            self.chunk.emit(Op::Pop, self.line);
                            let next_arm_target = self.chunk.code.len();
                            for skip in constraint_skips {
                                self.chunk.patch_jump_to(skip, scoped_fail_target);
                            }
                            self.chunk.patch_jump_to(skip_len, pre_scope_fail_target);
                            self.chunk.patch_jump_to(skip_type, pre_scope_fail_target);
                            self.chunk.patch_jump_to(next_arm_jump, next_arm_target);
                        }
                        // Literal/expression pattern — compare with Equal.
                        _ => {
                            self.chunk.emit(Op::Dup, self.line);
                            self.compile_node(&arm.pattern)?;
                            self.chunk.emit(Op::Equal, self.line);
                            let skip = self.chunk.emit_jump(Op::JumpIfFalse, self.line);
                            self.chunk.emit(Op::Pop, self.line);
                            if let Some(ref guard) = arm.guard {
                                self.compile_node(guard)?;
                                let guard_skip = self.chunk.emit_jump(Op::JumpIfFalse, self.line);
                                self.chunk.emit(Op::Pop, self.line);
                                self.begin_scope();
                                self.chunk.emit(Op::Pop, self.line);
                                self.compile_match_body(&arm.body)?;
                                self.end_scope();
                                end_jumps.push(self.chunk.emit_jump(Op::Jump, self.line));
                                self.chunk.patch_jump(guard_skip);
                                self.chunk.emit(Op::Pop, self.line);
                            } else {
                                self.begin_scope();
                                self.chunk.emit(Op::Pop, self.line);
                                self.compile_match_body(&arm.body)?;
                                self.end_scope();
                                end_jumps.push(self.chunk.emit_jump(Op::Jump, self.line));
                            }
                            self.chunk.patch_jump(skip);
                            self.chunk.emit(Op::Pop, self.line);
                        }
                    }
                }
                let msg_idx = self.chunk.add_constant(Constant::String(
                    "No match arm matched the value".to_string(),
                ));
                self.chunk.emit(Op::Pop, self.line);
                self.chunk.emit_u16(Op::Constant, msg_idx, self.line);
                self.chunk.emit(Op::Throw, self.line);
                for j in end_jumps {
                    self.chunk.patch_jump(j);
                }
            }

            Node::RangeExpr {
                start,
                end,
                inclusive,
            } => {
                let name_idx = self
                    .chunk
                    .add_constant(Constant::String("__range__".to_string()));
                self.chunk.emit_u16(Op::Constant, name_idx, self.line);
                self.compile_node(start)?;
                self.compile_node(end)?;
                if *inclusive {
                    self.chunk.emit(Op::True, self.line);
                } else {
                    self.chunk.emit(Op::False, self.line);
                }
                self.chunk.emit_u8(Op::Call, 3, self.line);
            }

            Node::GuardStmt {
                condition,
                else_body,
            } => {
                self.compile_node(condition)?;
                let skip_jump = self.chunk.emit_jump(Op::JumpIfTrue, self.line);
                self.chunk.emit(Op::Pop, self.line);
                self.compile_scoped_block(else_body)?;
                // Guard is a statement, not an expression: pop any trailing value.
                if !else_body.is_empty() && Self::produces_value(&else_body.last().unwrap().node) {
                    self.chunk.emit(Op::Pop, self.line);
                }
                let end_jump = self.chunk.emit_jump(Op::Jump, self.line);
                self.chunk.patch_jump(skip_jump);
                self.chunk.emit(Op::Pop, self.line);
                self.chunk.patch_jump(end_jump);
                self.chunk.emit(Op::Nil, self.line);
            }

            Node::RequireStmt { condition, message } => {
                self.compile_node(condition)?;
                let ok_jump = self.chunk.emit_jump(Op::JumpIfTrue, self.line);
                self.chunk.emit(Op::Pop, self.line);
                if let Some(message) = message {
                    self.compile_node(message)?;
                } else {
                    let idx = self
                        .chunk
                        .add_constant(Constant::String("require condition failed".to_string()));
                    self.chunk.emit_u16(Op::Constant, idx, self.line);
                }
                self.chunk.emit(Op::Throw, self.line);
                self.chunk.patch_jump(ok_jump);
                self.chunk.emit(Op::Pop, self.line);
            }

            Node::Block(stmts) => {
                self.compile_scoped_block(stmts)?;
            }

            Node::DeadlineBlock { duration, body } => {
                self.compile_node(duration)?;
                self.chunk.emit(Op::DeadlineSetup, self.line);
                self.compile_scoped_block(body)?;
                self.chunk.emit(Op::DeadlineEnd, self.line);
            }

            Node::MutexBlock { body } => {
                // v1: single-threaded, but still uses a lexical block scope.
                self.begin_scope();
                for sn in body {
                    self.compile_node(sn)?;
                    if Self::produces_value(&sn.node) {
                        self.chunk.emit(Op::Pop, self.line);
                    }
                }
                self.chunk.emit(Op::Nil, self.line);
                self.end_scope();
            }

            Node::DeferStmt { body } => {
                // Push onto the finally stack so it runs on return/throw/scope-exit.
                self.finally_bodies
                    .push(FinallyEntry::Finally(body.clone()));
                self.chunk.emit(Op::Nil, self.line);
            }

            Node::YieldExpr { value } => {
                if let Some(val) = value {
                    self.compile_node(val)?;
                } else {
                    self.chunk.emit(Op::Nil, self.line);
                }
                self.chunk.emit(Op::Yield, self.line);
            }

            Node::EnumConstruct {
                enum_name,
                variant,
                args,
            } => {
                for arg in args {
                    self.compile_node(arg)?;
                }
                let enum_idx = self.chunk.add_constant(Constant::String(enum_name.clone()));
                let var_idx = self.chunk.add_constant(Constant::String(variant.clone()));
                // BuildEnum operands: enum_name_idx, variant_idx, field_count.
                self.chunk.emit_u16(Op::BuildEnum, enum_idx, self.line);
                let hi = (var_idx >> 8) as u8;
                let lo = var_idx as u8;
                self.chunk.code.push(hi);
                self.chunk.code.push(lo);
                self.chunk.lines.push(self.line);
                self.chunk.columns.push(self.column);
                self.chunk.lines.push(self.line);
                self.chunk.columns.push(self.column);
                let fc = args.len() as u16;
                let fhi = (fc >> 8) as u8;
                let flo = fc as u8;
                self.chunk.code.push(fhi);
                self.chunk.code.push(flo);
                self.chunk.lines.push(self.line);
                self.chunk.columns.push(self.column);
                self.chunk.lines.push(self.line);
                self.chunk.columns.push(self.column);
            }

            Node::StructConstruct {
                struct_name,
                fields,
            } => {
                // Route through `__make_struct` so impl dispatch sees a StructInstance.
                let make_idx = self
                    .chunk
                    .add_constant(Constant::String("__make_struct".to_string()));
                let struct_name_idx = self
                    .chunk
                    .add_constant(Constant::String(struct_name.clone()));
                self.chunk.emit_u16(Op::Constant, make_idx, self.line);
                self.chunk
                    .emit_u16(Op::Constant, struct_name_idx, self.line);

                for entry in fields {
                    self.compile_node(&entry.key)?;
                    self.compile_node(&entry.value)?;
                }
                self.chunk
                    .emit_u16(Op::BuildDict, fields.len() as u16, self.line);
                self.chunk.emit_u8(Op::Call, 2, self.line);
            }

            Node::ImportDecl { path } => {
                let idx = self.chunk.add_constant(Constant::String(path.clone()));
                self.chunk.emit_u16(Op::Import, idx, self.line);
            }

            Node::SelectiveImport { names, path } => {
                let path_idx = self.chunk.add_constant(Constant::String(path.clone()));
                let names_str = names.join(",");
                let names_idx = self.chunk.add_constant(Constant::String(names_str));
                self.chunk
                    .emit_u16(Op::SelectiveImport, path_idx, self.line);
                let hi = (names_idx >> 8) as u8;
                let lo = names_idx as u8;
                self.chunk.code.push(hi);
                self.chunk.code.push(lo);
                self.chunk.lines.push(self.line);
                self.chunk.columns.push(self.column);
                self.chunk.lines.push(self.line);
                self.chunk.columns.push(self.column);
            }

            Node::TryOperator { operand } => {
                self.compile_node(operand)?;
                self.chunk.emit(Op::TryUnwrap, self.line);
            }

            Node::ImplBlock { type_name, methods } => {
                // Lower into a `__impl_TypeName` dict of name -> closure.
                for method_sn in methods {
                    if let Node::FnDecl {
                        name, params, body, ..
                    } = &method_sn.node
                    {
                        let key_idx = self.chunk.add_constant(Constant::String(name.clone()));
                        self.chunk.emit_u16(Op::Constant, key_idx, self.line);

                        let mut fn_compiler = Compiler::new();
                        fn_compiler.enum_names = self.enum_names.clone();
                        fn_compiler.emit_default_preamble(params)?;
                        fn_compiler.emit_type_checks(params);
                        fn_compiler.compile_block(body)?;
                        fn_compiler.chunk.emit(Op::Nil, self.line);
                        fn_compiler.chunk.emit(Op::Return, self.line);

                        let func = CompiledFunction {
                            name: format!("{}.{}", type_name, name),
                            params: TypedParam::names(params),
                            default_start: TypedParam::default_start(params),
                            chunk: fn_compiler.chunk,
                            is_generator: false,
                            has_rest_param: false,
                        };
                        let fn_idx = self.chunk.functions.len();
                        self.chunk.functions.push(func);
                        self.chunk.emit_u16(Op::Closure, fn_idx as u16, self.line);
                    }
                }
                let method_count = methods
                    .iter()
                    .filter(|m| matches!(m.node, Node::FnDecl { .. }))
                    .count();
                self.chunk
                    .emit_u16(Op::BuildDict, method_count as u16, self.line);
                let impl_name = format!("__impl_{}", type_name);
                let name_idx = self.chunk.add_constant(Constant::String(impl_name));
                self.chunk.emit_u16(Op::DefLet, name_idx, self.line);
            }

            Node::StructDecl { name, .. } => {
                // Emit a constructor: StructName({field: val, ...}) -> StructInstance.
                let mut fn_compiler = Compiler::new();
                fn_compiler.enum_names = self.enum_names.clone();
                let params = vec![TypedParam::untyped("__fields")];
                fn_compiler.emit_default_preamble(&params)?;

                let make_idx = fn_compiler
                    .chunk
                    .add_constant(Constant::String("__make_struct".into()));
                fn_compiler
                    .chunk
                    .emit_u16(Op::Constant, make_idx, self.line);
                let sname_idx = fn_compiler
                    .chunk
                    .add_constant(Constant::String(name.clone()));
                fn_compiler
                    .chunk
                    .emit_u16(Op::Constant, sname_idx, self.line);
                let fields_idx = fn_compiler
                    .chunk
                    .add_constant(Constant::String("__fields".into()));
                fn_compiler
                    .chunk
                    .emit_u16(Op::GetVar, fields_idx, self.line);
                fn_compiler.chunk.emit_u8(Op::Call, 2, self.line);
                fn_compiler.chunk.emit(Op::Return, self.line);

                let func = CompiledFunction {
                    name: name.clone(),
                    params: TypedParam::names(&params),
                    default_start: None,
                    chunk: fn_compiler.chunk,
                    is_generator: false,
                    has_rest_param: false,
                };
                let fn_idx = self.chunk.functions.len();
                self.chunk.functions.push(func);
                self.chunk.emit_u16(Op::Closure, fn_idx as u16, self.line);
                let name_idx = self.chunk.add_constant(Constant::String(name.clone()));
                self.chunk.emit_u16(Op::DefLet, name_idx, self.line);
            }

            // Metadata-only declarations (no runtime effect).
            Node::Pipeline { .. }
            | Node::OverrideDecl { .. }
            | Node::TypeDecl { .. }
            | Node::EnumDecl { .. }
            | Node::InterfaceDecl { .. } => {
                self.chunk.emit(Op::Nil, self.line);
            }

            Node::TryCatch {
                body,
                error_var,
                error_type,
                catch_body,
                finally_body,
            } => {
                // Extract the type name for typed catch (e.g., "AppError")
                let type_name = error_type.as_ref().and_then(|te| {
                    if let harn_parser::TypeExpr::Named(name) = te {
                        Some(name.clone())
                    } else {
                        None
                    }
                });

                let type_name_idx = if let Some(ref tn) = type_name {
                    self.chunk.add_constant(Constant::String(tn.clone()))
                } else {
                    self.chunk.add_constant(Constant::String(String::new()))
                };

                let has_catch = !catch_body.is_empty() || error_var.is_some();
                let has_finally = finally_body.is_some();

                if has_catch && has_finally {
                    let finally_body = finally_body.as_ref().unwrap();
                    // During the try body: install both the catch barrier
                    // (so throws don't pre-run finallys beyond our catch)
                    // and our finally (so return/break/continue in the
                    // body still run it). Order matters — barrier is below
                    // our finally so pre-running stops *at* the barrier.
                    self.finally_bodies.push(FinallyEntry::CatchBarrier);
                    self.finally_bodies
                        .push(FinallyEntry::Finally(finally_body.clone()));

                    self.handler_depth += 1;
                    let catch_jump = self.chunk.emit_jump(Op::TryCatchSetup, self.line);
                    self.emit_type_name_extra(type_name_idx);

                    self.compile_try_body(body)?;

                    self.handler_depth -= 1;
                    self.chunk.emit(Op::PopHandler, self.line);
                    // Body-success path: throw never fired, so pre-run did
                    // not happen. Run finally now.
                    self.compile_finally_inline(finally_body)?;
                    // Drop both finally and barrier — we're leaving the
                    // try body; the catch handler compiles without them.
                    self.finally_bodies.pop(); // Finally
                    self.finally_bodies.pop(); // CatchBarrier
                    let end_jump = self.chunk.emit_jump(Op::Jump, self.line);

                    self.chunk.patch_jump(catch_jump);
                    self.begin_scope();
                    self.compile_catch_binding(error_var)?;

                    // Inner try around catch body so a catch-body throw
                    // lands in our `rethrow_jump` and we emit a plain
                    // rethrow (finally already fired via the body's throw).
                    self.handler_depth += 1;
                    let rethrow_jump = self.chunk.emit_jump(Op::TryCatchSetup, self.line);
                    let empty_type = self.chunk.add_constant(Constant::String(String::new()));
                    self.emit_type_name_extra(empty_type);

                    self.compile_try_body(catch_body)?;

                    self.handler_depth -= 1;
                    self.chunk.emit(Op::PopHandler, self.line);
                    self.end_scope();
                    let end_jump2 = self.chunk.emit_jump(Op::Jump, self.line);

                    // Rethrow handler: plain rethrow; finally already pre-ran
                    // via the body's Throw lowering before the outer handler
                    // delivered control into catch.
                    self.chunk.patch_jump(rethrow_jump);
                    self.compile_plain_rethrow()?;
                    self.end_scope();

                    self.chunk.patch_jump(end_jump);
                    self.chunk.patch_jump(end_jump2);
                } else if has_finally {
                    let finally_body = finally_body.as_ref().unwrap();
                    // No catch: throws in the body unwind through us, so
                    // we don't install a barrier — our finally and any
                    // outer finallys are on the throw's escape path.
                    self.finally_bodies
                        .push(FinallyEntry::Finally(finally_body.clone()));

                    self.handler_depth += 1;
                    let error_jump = self.chunk.emit_jump(Op::TryCatchSetup, self.line);
                    let empty_type = self.chunk.add_constant(Constant::String(String::new()));
                    self.emit_type_name_extra(empty_type);

                    self.compile_try_body(body)?;

                    self.handler_depth -= 1;
                    self.chunk.emit(Op::PopHandler, self.line);
                    self.compile_finally_inline(finally_body)?;
                    let end_jump = self.chunk.emit_jump(Op::Jump, self.line);

                    // Error path: save error, re-throw. Finally already
                    // pre-ran via the body's Throw lowering.
                    self.chunk.patch_jump(error_jump);
                    self.compile_plain_rethrow()?;

                    self.chunk.patch_jump(end_jump);

                    self.finally_bodies.pop(); // Finally
                } else {
                    // try-catch without finally: install a barrier so
                    // throws in the body don't pre-run outer finallys
                    // (the throw is caught here and won't unwind past).
                    self.finally_bodies.push(FinallyEntry::CatchBarrier);

                    self.handler_depth += 1;
                    let catch_jump = self.chunk.emit_jump(Op::TryCatchSetup, self.line);
                    self.emit_type_name_extra(type_name_idx);

                    self.compile_try_body(body)?;

                    self.handler_depth -= 1;
                    self.chunk.emit(Op::PopHandler, self.line);
                    self.finally_bodies.pop(); // CatchBarrier
                    let end_jump = self.chunk.emit_jump(Op::Jump, self.line);

                    self.chunk.patch_jump(catch_jump);
                    self.begin_scope();
                    self.compile_catch_binding(error_var)?;

                    self.compile_try_body(catch_body)?;
                    self.end_scope();

                    self.chunk.patch_jump(end_jump);
                }
            }

            Node::TryExpr { body } => {
                // `try { body }` returns Result.Ok(value) or Result.Err(error).
                self.handler_depth += 1;
                let catch_jump = self.chunk.emit_jump(Op::TryCatchSetup, self.line);
                let empty_type = self.chunk.add_constant(Constant::String(String::new()));
                self.emit_type_name_extra(empty_type);

                self.compile_try_body(body)?;

                self.handler_depth -= 1;
                self.chunk.emit(Op::PopHandler, self.line);

                // Wrap success in Result.Ok.
                let ok_idx = self.chunk.add_constant(Constant::String("Ok".to_string()));
                self.chunk.emit_u16(Op::Constant, ok_idx, self.line);
                self.chunk.emit(Op::Swap, self.line);
                self.chunk.emit_u8(Op::Call, 1, self.line);

                let end_jump = self.chunk.emit_jump(Op::Jump, self.line);

                // Error path: wrap in Result.Err.
                self.chunk.patch_jump(catch_jump);

                let err_idx = self.chunk.add_constant(Constant::String("Err".to_string()));
                self.chunk.emit_u16(Op::Constant, err_idx, self.line);
                self.chunk.emit(Op::Swap, self.line);
                self.chunk.emit_u8(Op::Call, 1, self.line);

                self.chunk.patch_jump(end_jump);
            }

            Node::Retry { count, body } => {
                self.compile_node(count)?;
                let counter_name = "__retry_counter__";
                let counter_idx = self
                    .chunk
                    .add_constant(Constant::String(counter_name.to_string()));
                self.chunk.emit_u16(Op::DefVar, counter_idx, self.line);

                // Store last error for re-throwing after retries are exhausted.
                self.chunk.emit(Op::Nil, self.line);
                let err_name = "__retry_last_error__";
                let err_idx = self
                    .chunk
                    .add_constant(Constant::String(err_name.to_string()));
                self.chunk.emit_u16(Op::DefVar, err_idx, self.line);

                let loop_start = self.chunk.current_offset();

                let catch_jump = self.chunk.emit_jump(Op::TryCatchSetup, self.line);
                // Empty type name → untyped catch.
                let empty_type = self.chunk.add_constant(Constant::String(String::new()));
                let hi = (empty_type >> 8) as u8;
                let lo = empty_type as u8;
                self.chunk.code.push(hi);
                self.chunk.code.push(lo);
                self.chunk.lines.push(self.line);
                self.chunk.columns.push(self.column);
                self.chunk.lines.push(self.line);
                self.chunk.columns.push(self.column);

                self.compile_block(body)?;

                self.chunk.emit(Op::PopHandler, self.line);
                let end_jump = self.chunk.emit_jump(Op::Jump, self.line);

                self.chunk.patch_jump(catch_jump);
                self.chunk.emit(Op::Dup, self.line);
                self.chunk.emit_u16(Op::SetVar, err_idx, self.line);
                self.chunk.emit(Op::Pop, self.line);

                self.chunk.emit_u16(Op::GetVar, counter_idx, self.line);
                let one_idx = self.chunk.add_constant(Constant::Int(1));
                self.chunk.emit_u16(Op::Constant, one_idx, self.line);
                self.chunk.emit(Op::Sub, self.line);
                self.chunk.emit(Op::Dup, self.line);
                self.chunk.emit_u16(Op::SetVar, counter_idx, self.line);

                let zero_idx = self.chunk.add_constant(Constant::Int(0));
                self.chunk.emit_u16(Op::Constant, zero_idx, self.line);
                self.chunk.emit(Op::Greater, self.line);
                let retry_jump = self.chunk.emit_jump(Op::JumpIfFalse, self.line);
                self.chunk.emit(Op::Pop, self.line);
                self.chunk.emit_u16(Op::Jump, loop_start as u16, self.line);

                // Retries exhausted — re-throw the last error.
                self.chunk.patch_jump(retry_jump);
                self.chunk.emit(Op::Pop, self.line);
                self.chunk.emit_u16(Op::GetVar, err_idx, self.line);
                self.chunk.emit(Op::Throw, self.line);

                self.chunk.patch_jump(end_jump);
                self.chunk.emit(Op::Nil, self.line);
            }

            Node::Parallel {
                mode,
                expr,
                variable,
                body,
                options,
            } => {
                // Push the `max_concurrent` cap first so the runtime
                // opcodes can pop it beneath the iterable + closure. A
                // cap of 0 (or a missing `with { ... }` clause) means
                // "unlimited". Unknown option keys are parser errors.
                let cap_expr = options
                    .iter()
                    .find(|(key, _)| key == "max_concurrent")
                    .map(|(_, value)| value);
                if let Some(cap_expr) = cap_expr {
                    self.compile_node(cap_expr)?;
                } else {
                    let zero_idx = self.chunk.add_constant(Constant::Int(0));
                    self.chunk.emit_u16(Op::Constant, zero_idx, self.line);
                }
                self.compile_node(expr)?;
                let mut fn_compiler = Compiler::new();
                fn_compiler.enum_names = self.enum_names.clone();
                fn_compiler.compile_block(body)?;
                fn_compiler.chunk.emit(Op::Return, self.line);
                let (fn_name, params) = match mode {
                    ParallelMode::Count => (
                        "<parallel>",
                        vec![variable.clone().unwrap_or_else(|| "__i__".to_string())],
                    ),
                    ParallelMode::Each => (
                        "<parallel_each>",
                        vec![variable.clone().unwrap_or_else(|| "__item__".to_string())],
                    ),
                    ParallelMode::Settle => (
                        "<parallel_settle>",
                        vec![variable.clone().unwrap_or_else(|| "__item__".to_string())],
                    ),
                };
                let func = CompiledFunction {
                    name: fn_name.to_string(),
                    params,
                    default_start: None,
                    chunk: fn_compiler.chunk,
                    is_generator: false,
                    has_rest_param: false,
                };
                let fn_idx = self.chunk.functions.len();
                self.chunk.functions.push(func);
                self.chunk.emit_u16(Op::Closure, fn_idx as u16, self.line);
                let op = match mode {
                    ParallelMode::Count => Op::Parallel,
                    ParallelMode::Each => Op::ParallelMap,
                    ParallelMode::Settle => Op::ParallelSettle,
                };
                self.chunk.emit(op, self.line);
            }

            Node::SpawnExpr { body } => {
                let mut fn_compiler = Compiler::new();
                fn_compiler.enum_names = self.enum_names.clone();
                fn_compiler.compile_block(body)?;
                fn_compiler.chunk.emit(Op::Return, self.line);
                let func = CompiledFunction {
                    name: "<spawn>".to_string(),
                    params: vec![],
                    default_start: None,
                    chunk: fn_compiler.chunk,
                    is_generator: false,
                    has_rest_param: false,
                };
                let fn_idx = self.chunk.functions.len();
                self.chunk.functions.push(func);
                self.chunk.emit_u16(Op::Closure, fn_idx as u16, self.line);
                self.chunk.emit(Op::Spawn, self.line);
            }
            Node::SelectExpr {
                cases,
                timeout,
                default_body,
            } => {
                // Desugar `select` into a builtin call returning a dict with
                // {index, value}, then dispatch on result.index. `index == -1`
                // means timeout / default fell through.
                let builtin_name = if timeout.is_some() {
                    "__select_timeout"
                } else if default_body.is_some() {
                    "__select_try"
                } else {
                    "__select_list"
                };

                let name_idx = self
                    .chunk
                    .add_constant(Constant::String(builtin_name.into()));
                self.chunk.emit_u16(Op::Constant, name_idx, self.line);

                for case in cases {
                    self.compile_node(&case.channel)?;
                }
                self.chunk
                    .emit_u16(Op::BuildList, cases.len() as u16, self.line);

                if let Some((duration_expr, _)) = timeout {
                    self.compile_node(duration_expr)?;
                    self.chunk.emit_u8(Op::Call, 2, self.line);
                } else {
                    self.chunk.emit_u8(Op::Call, 1, self.line);
                }

                self.temp_counter += 1;
                let result_name = format!("__sel_result_{}__", self.temp_counter);
                let result_idx = self
                    .chunk
                    .add_constant(Constant::String(result_name.clone()));
                self.chunk.emit_u16(Op::DefVar, result_idx, self.line);

                let mut end_jumps = Vec::new();

                for (i, case) in cases.iter().enumerate() {
                    let get_r = self
                        .chunk
                        .add_constant(Constant::String(result_name.clone()));
                    self.chunk.emit_u16(Op::GetVar, get_r, self.line);
                    let idx_prop = self.chunk.add_constant(Constant::String("index".into()));
                    self.chunk.emit_u16(Op::GetProperty, idx_prop, self.line);
                    let case_i = self.chunk.add_constant(Constant::Int(i as i64));
                    self.chunk.emit_u16(Op::Constant, case_i, self.line);
                    self.chunk.emit(Op::Equal, self.line);
                    let skip = self.chunk.emit_jump(Op::JumpIfFalse, self.line);
                    self.chunk.emit(Op::Pop, self.line);
                    self.begin_scope();

                    let get_r2 = self
                        .chunk
                        .add_constant(Constant::String(result_name.clone()));
                    self.chunk.emit_u16(Op::GetVar, get_r2, self.line);
                    let val_prop = self.chunk.add_constant(Constant::String("value".into()));
                    self.chunk.emit_u16(Op::GetProperty, val_prop, self.line);
                    let var_idx = self
                        .chunk
                        .add_constant(Constant::String(case.variable.clone()));
                    self.chunk.emit_u16(Op::DefLet, var_idx, self.line);

                    self.compile_try_body(&case.body)?;
                    self.end_scope();
                    end_jumps.push(self.chunk.emit_jump(Op::Jump, self.line));
                    self.chunk.patch_jump(skip);
                    self.chunk.emit(Op::Pop, self.line);
                }

                if let Some((_, ref timeout_body)) = timeout {
                    self.compile_try_body(timeout_body)?;
                } else if let Some(ref def_body) = default_body {
                    self.compile_try_body(def_body)?;
                } else {
                    self.chunk.emit(Op::Nil, self.line);
                }

                for ej in end_jumps {
                    self.chunk.patch_jump(ej);
                }
            }
            Node::Spread(_) => {
                return Err(CompileError {
                    message: "spread (...) can only be used inside list literals, dict literals, or function call arguments".into(),
                    line: self.line,
                });
            }
        }
        Ok(())
    }

    /// Compile a destructuring binding pattern.
    /// Expects the RHS value to already be on the stack.
    /// After this, the value is consumed (popped) and each binding is defined.
    fn compile_destructuring(
        &mut self,
        pattern: &BindingPattern,
        is_mutable: bool,
    ) -> Result<(), CompileError> {
        let def_op = if is_mutable { Op::DefVar } else { Op::DefLet };
        match pattern {
            BindingPattern::Identifier(name) => {
                let idx = self.chunk.add_constant(Constant::String(name.clone()));
                self.chunk.emit_u16(def_op, idx, self.line);
            }
            BindingPattern::Dict(fields) => {
                // Runtime `__assert_dict(value)` type check on the RHS.
                self.chunk.emit(Op::Dup, self.line);
                let assert_idx = self
                    .chunk
                    .add_constant(Constant::String("__assert_dict".into()));
                self.chunk.emit_u16(Op::Constant, assert_idx, self.line);
                self.chunk.emit(Op::Swap, self.line);
                self.chunk.emit_u8(Op::Call, 1, self.line);
                self.chunk.emit(Op::Pop, self.line);

                let non_rest: Vec<_> = fields.iter().filter(|f| !f.is_rest).collect();
                let rest_field = fields.iter().find(|f| f.is_rest);

                for field in &non_rest {
                    self.chunk.emit(Op::Dup, self.line);
                    let key_idx = self.chunk.add_constant(Constant::String(field.key.clone()));
                    self.chunk.emit_u16(Op::Constant, key_idx, self.line);
                    self.chunk.emit(Op::Subscript, self.line);
                    if let Some(default_expr) = &field.default_value {
                        // Nil-coalescing: use default when the field was nil.
                        self.chunk.emit(Op::Dup, self.line);
                        self.chunk.emit(Op::Nil, self.line);
                        self.chunk.emit(Op::NotEqual, self.line);
                        let skip_default = self.chunk.emit_jump(Op::JumpIfTrue, self.line);
                        self.chunk.emit(Op::Pop, self.line);
                        self.chunk.emit(Op::Pop, self.line);
                        self.compile_node(default_expr)?;
                        let end = self.chunk.emit_jump(Op::Jump, self.line);
                        self.chunk.patch_jump(skip_default);
                        self.chunk.emit(Op::Pop, self.line);
                        self.chunk.patch_jump(end);
                    }
                    let binding_name = field.alias.as_deref().unwrap_or(&field.key);
                    let name_idx = self
                        .chunk
                        .add_constant(Constant::String(binding_name.to_string()));
                    self.chunk.emit_u16(def_op, name_idx, self.line);
                }

                if let Some(rest) = rest_field {
                    // `__dict_rest(dict, [keys_to_exclude])`.
                    let fn_idx = self
                        .chunk
                        .add_constant(Constant::String("__dict_rest".into()));
                    self.chunk.emit_u16(Op::Constant, fn_idx, self.line);
                    self.chunk.emit(Op::Swap, self.line);
                    for field in &non_rest {
                        let key_idx = self.chunk.add_constant(Constant::String(field.key.clone()));
                        self.chunk.emit_u16(Op::Constant, key_idx, self.line);
                    }
                    self.chunk
                        .emit_u16(Op::BuildList, non_rest.len() as u16, self.line);
                    self.chunk.emit_u8(Op::Call, 2, self.line);
                    let rest_name = &rest.key;
                    let rest_idx = self.chunk.add_constant(Constant::String(rest_name.clone()));
                    self.chunk.emit_u16(def_op, rest_idx, self.line);
                } else {
                    self.chunk.emit(Op::Pop, self.line);
                }
            }
            BindingPattern::Pair(first_name, second_name) => {
                self.chunk.emit(Op::Dup, self.line);
                let first_key_idx = self
                    .chunk
                    .add_constant(Constant::String("first".to_string()));
                self.chunk
                    .emit_u16(Op::GetProperty, first_key_idx, self.line);
                let first_name_idx = self
                    .chunk
                    .add_constant(Constant::String(first_name.clone()));
                self.chunk.emit_u16(def_op, first_name_idx, self.line);

                let second_key_idx = self
                    .chunk
                    .add_constant(Constant::String("second".to_string()));
                self.chunk
                    .emit_u16(Op::GetProperty, second_key_idx, self.line);
                let second_name_idx = self
                    .chunk
                    .add_constant(Constant::String(second_name.clone()));
                self.chunk.emit_u16(def_op, second_name_idx, self.line);
                // No trailing Pop: GetProperty consumed the source pair.
            }
            BindingPattern::List(elements) => {
                // Runtime `__assert_list(value)` type check on the RHS.
                self.chunk.emit(Op::Dup, self.line);
                let assert_idx = self
                    .chunk
                    .add_constant(Constant::String("__assert_list".into()));
                self.chunk.emit_u16(Op::Constant, assert_idx, self.line);
                self.chunk.emit(Op::Swap, self.line);
                self.chunk.emit_u8(Op::Call, 1, self.line);
                self.chunk.emit(Op::Pop, self.line);

                let non_rest: Vec<_> = elements.iter().filter(|e| !e.is_rest).collect();
                let rest_elem = elements.iter().find(|e| e.is_rest);

                for (i, elem) in non_rest.iter().enumerate() {
                    self.chunk.emit(Op::Dup, self.line);
                    let idx_const = self.chunk.add_constant(Constant::Int(i as i64));
                    self.chunk.emit_u16(Op::Constant, idx_const, self.line);
                    self.chunk.emit(Op::Subscript, self.line);
                    if let Some(default_expr) = &elem.default_value {
                        // Nil-coalescing: use default when the slot was nil.
                        self.chunk.emit(Op::Dup, self.line);
                        self.chunk.emit(Op::Nil, self.line);
                        self.chunk.emit(Op::NotEqual, self.line);
                        let skip_default = self.chunk.emit_jump(Op::JumpIfTrue, self.line);
                        self.chunk.emit(Op::Pop, self.line);
                        self.chunk.emit(Op::Pop, self.line);
                        self.compile_node(default_expr)?;
                        let end = self.chunk.emit_jump(Op::Jump, self.line);
                        self.chunk.patch_jump(skip_default);
                        self.chunk.emit(Op::Pop, self.line);
                        self.chunk.patch_jump(end);
                    }
                    let name_idx = self.chunk.add_constant(Constant::String(elem.name.clone()));
                    self.chunk.emit_u16(def_op, name_idx, self.line);
                }

                if let Some(rest) = rest_elem {
                    // Slice list[n..] where n = non_rest.len(); Slice expects
                    // object, start, end on the stack.
                    let start_idx = self
                        .chunk
                        .add_constant(Constant::Int(non_rest.len() as i64));
                    self.chunk.emit_u16(Op::Constant, start_idx, self.line);
                    self.chunk.emit(Op::Nil, self.line);
                    self.chunk.emit(Op::Slice, self.line);
                    let rest_name_idx =
                        self.chunk.add_constant(Constant::String(rest.name.clone()));
                    self.chunk.emit_u16(def_op, rest_name_idx, self.line);
                } else {
                    self.chunk.emit(Op::Pop, self.line);
                }
            }
        }
        Ok(())
    }

    /// Check if a node produces a value on the stack that needs to be popped.
    fn produces_value(node: &Node) -> bool {
        match node {
            Node::LetBinding { .. }
            | Node::VarBinding { .. }
            | Node::Assignment { .. }
            | Node::ReturnStmt { .. }
            | Node::FnDecl { .. }
            | Node::ToolDecl { .. }
            | Node::ImplBlock { .. }
            | Node::StructDecl { .. }
            | Node::EnumDecl { .. }
            | Node::InterfaceDecl { .. }
            | Node::TypeDecl { .. }
            | Node::ThrowStmt { .. }
            | Node::BreakStmt
            | Node::ContinueStmt
            | Node::RequireStmt { .. }
            | Node::DeferStmt { .. } => false,
            Node::TryCatch { .. }
            | Node::TryExpr { .. }
            | Node::Retry { .. }
            | Node::GuardStmt { .. }
            | Node::DeadlineBlock { .. }
            | Node::MutexBlock { .. }
            | Node::Spread(_) => true,
            _ => true,
        }
    }
}

impl Compiler {
    /// Compile a function body into a CompiledFunction (for import support).
    ///
    /// This path is used when a module is imported and its top-level `fn`
    /// declarations are loaded into the importer's environment. It MUST emit
    /// the same function preamble as the in-file `Node::FnDecl` path, or
    /// imported functions will behave differently from locally-defined ones —
    /// in particular, default parameter values would never be set and typed
    /// parameters would not be runtime-checked.
    ///
    /// `source_file`, when provided, tags the resulting chunk so runtime
    /// errors can attribute frames to the imported file rather than the
    /// entry-point pipeline.
    pub fn compile_fn_body(
        &mut self,
        params: &[TypedParam],
        body: &[SNode],
        source_file: Option<String>,
    ) -> Result<CompiledFunction, CompileError> {
        let mut fn_compiler = Compiler::new();
        fn_compiler.enum_names = self.enum_names.clone();
        fn_compiler.emit_default_preamble(params)?;
        fn_compiler.emit_type_checks(params);
        let is_gen = body_contains_yield(body);
        fn_compiler.compile_block(body)?;
        fn_compiler.chunk.emit(Op::Nil, 0);
        fn_compiler.chunk.emit(Op::Return, 0);
        fn_compiler.chunk.source_file = source_file;
        Ok(CompiledFunction {
            name: String::new(),
            params: TypedParam::names(params),
            default_start: TypedParam::default_start(params),
            chunk: fn_compiler.chunk,
            is_generator: is_gen,
            has_rest_param: false,
        })
    }

    /// Compile a match arm body, ensuring it always pushes exactly one value.
    fn compile_match_body(&mut self, body: &[SNode]) -> Result<(), CompileError> {
        self.begin_scope();
        if body.is_empty() {
            self.chunk.emit(Op::Nil, self.line);
        } else {
            self.compile_block(body)?;
            if !Self::produces_value(&body.last().unwrap().node) {
                self.chunk.emit(Op::Nil, self.line);
            }
        }
        self.end_scope();
        Ok(())
    }

    /// Emit the binary op instruction for a compound assignment operator.
    fn emit_compound_op(&mut self, op: &str) -> Result<(), CompileError> {
        match op {
            "+" => self.chunk.emit(Op::Add, self.line),
            "-" => self.chunk.emit(Op::Sub, self.line),
            "*" => self.chunk.emit(Op::Mul, self.line),
            "/" => self.chunk.emit(Op::Div, self.line),
            "%" => self.chunk.emit(Op::Mod, self.line),
            _ => {
                return Err(CompileError {
                    message: format!("Unknown compound operator: {op}"),
                    line: self.line,
                })
            }
        }
        Ok(())
    }

    /// Extract the root variable name from a (possibly nested) access expression.
    fn root_var_name(&self, node: &SNode) -> Option<String> {
        match &node.node {
            Node::Identifier(name) => Some(name.clone()),
            Node::PropertyAccess { object, .. } | Node::OptionalPropertyAccess { object, .. } => {
                self.root_var_name(object)
            }
            Node::SubscriptAccess { object, .. } => self.root_var_name(object),
            _ => None,
        }
    }

    fn compile_top_level_declarations(&mut self, program: &[SNode]) -> Result<(), CompileError> {
        // Phase 1: evaluate module-level `let` / `var` bindings first, in
        // source order. This ensures function closures compiled in phase 2
        // capture these names in their env snapshot via `Op::Closure` —
        // fixing the "Undefined variable: FOO" surprise where a top-level
        // `let FOO = "..."` was silently dropped because it wasn't in this
        // match list. Keep in step with the import-time init path in
        // `crates/harn-vm/src/vm/imports.rs` (`module_state` construction).
        for sn in program {
            if matches!(&sn.node, Node::LetBinding { .. } | Node::VarBinding { .. }) {
                self.compile_node(sn)?;
            }
        }
        // Phase 2: compile type and function declarations. Function closures
        // created here capture the current env which now includes the
        // module-level bindings from phase 1.
        for sn in program {
            if matches!(
                &sn.node,
                Node::FnDecl { .. }
                    | Node::ToolDecl { .. }
                    | Node::ImplBlock { .. }
                    | Node::StructDecl { .. }
                    | Node::EnumDecl { .. }
                    | Node::InterfaceDecl { .. }
                    | Node::TypeDecl { .. }
            ) {
                self.compile_node(sn)?;
            }
        }
        Ok(())
    }
}

impl Compiler {
    /// Recursively collect all enum type names from the AST.
    fn collect_enum_names(nodes: &[SNode], names: &mut std::collections::HashSet<String>) {
        for sn in nodes {
            match &sn.node {
                Node::EnumDecl { name, .. } => {
                    names.insert(name.clone());
                }
                Node::Pipeline { body, .. } => {
                    Self::collect_enum_names(body, names);
                }
                Node::FnDecl { body, .. } | Node::ToolDecl { body, .. } => {
                    Self::collect_enum_names(body, names);
                }
                Node::Block(stmts) => {
                    Self::collect_enum_names(stmts, names);
                }
                _ => {}
            }
        }
    }

    fn collect_interface_methods(
        nodes: &[SNode],
        interfaces: &mut std::collections::HashMap<String, Vec<String>>,
    ) {
        for sn in nodes {
            match &sn.node {
                Node::InterfaceDecl { name, methods, .. } => {
                    let method_names: Vec<String> =
                        methods.iter().map(|m| m.name.clone()).collect();
                    interfaces.insert(name.clone(), method_names);
                }
                Node::Pipeline { body, .. }
                | Node::FnDecl { body, .. }
                | Node::ToolDecl { body, .. } => {
                    Self::collect_interface_methods(body, interfaces);
                }
                Node::Block(stmts) => {
                    Self::collect_interface_methods(stmts, interfaces);
                }
                _ => {}
            }
        }
    }
}

impl Default for Compiler {
    fn default() -> Self {
        Self::new()
    }
}

/// Check if a list of AST nodes contains any `yield` expression (used to detect generator functions).
fn body_contains_yield(nodes: &[SNode]) -> bool {
    nodes.iter().any(|sn| node_contains_yield(&sn.node))
}

fn node_contains_yield(node: &Node) -> bool {
    match node {
        Node::YieldExpr { .. } => true,
        // Don't recurse into nested fn/closure: yield in a nested fn does
        // NOT make the outer a generator.
        Node::FnDecl { .. } | Node::Closure { .. } => false,
        Node::Block(stmts) => body_contains_yield(stmts),
        Node::IfElse {
            condition,
            then_body,
            else_body,
        } => {
            node_contains_yield(&condition.node)
                || body_contains_yield(then_body)
                || else_body.as_ref().is_some_and(|b| body_contains_yield(b))
        }
        Node::WhileLoop { condition, body } => {
            node_contains_yield(&condition.node) || body_contains_yield(body)
        }
        Node::ForIn { iterable, body, .. } => {
            node_contains_yield(&iterable.node) || body_contains_yield(body)
        }
        Node::TryCatch {
            body, catch_body, ..
        } => body_contains_yield(body) || body_contains_yield(catch_body),
        Node::TryExpr { body } => body_contains_yield(body),
        _ => false,
    }
}

/// Check if an AST node contains `_` identifier (pipe placeholder).
fn contains_pipe_placeholder(node: &SNode) -> bool {
    match &node.node {
        Node::Identifier(name) if name == "_" => true,
        Node::FunctionCall { args, .. } => args.iter().any(contains_pipe_placeholder),
        Node::MethodCall { object, args, .. } => {
            contains_pipe_placeholder(object) || args.iter().any(contains_pipe_placeholder)
        }
        Node::BinaryOp { left, right, .. } => {
            contains_pipe_placeholder(left) || contains_pipe_placeholder(right)
        }
        Node::UnaryOp { operand, .. } => contains_pipe_placeholder(operand),
        Node::ListLiteral(items) => items.iter().any(contains_pipe_placeholder),
        Node::PropertyAccess { object, .. } => contains_pipe_placeholder(object),
        Node::SubscriptAccess { object, index } => {
            contains_pipe_placeholder(object) || contains_pipe_placeholder(index)
        }
        _ => false,
    }
}

/// Replace all `_` identifiers with `__pipe` in an AST node (for pipe placeholder desugaring).
fn replace_pipe_placeholder(node: &SNode) -> SNode {
    let new_node = match &node.node {
        Node::Identifier(name) if name == "_" => Node::Identifier("__pipe".into()),
        Node::FunctionCall { name, args } => Node::FunctionCall {
            name: name.clone(),
            args: args.iter().map(replace_pipe_placeholder).collect(),
        },
        Node::MethodCall {
            object,
            method,
            args,
        } => Node::MethodCall {
            object: Box::new(replace_pipe_placeholder(object)),
            method: method.clone(),
            args: args.iter().map(replace_pipe_placeholder).collect(),
        },
        Node::BinaryOp { op, left, right } => Node::BinaryOp {
            op: op.clone(),
            left: Box::new(replace_pipe_placeholder(left)),
            right: Box::new(replace_pipe_placeholder(right)),
        },
        Node::UnaryOp { op, operand } => Node::UnaryOp {
            op: op.clone(),
            operand: Box::new(replace_pipe_placeholder(operand)),
        },
        Node::ListLiteral(items) => {
            Node::ListLiteral(items.iter().map(replace_pipe_placeholder).collect())
        }
        Node::PropertyAccess { object, property } => Node::PropertyAccess {
            object: Box::new(replace_pipe_placeholder(object)),
            property: property.clone(),
        },
        Node::SubscriptAccess { object, index } => Node::SubscriptAccess {
            object: Box::new(replace_pipe_placeholder(object)),
            index: Box::new(replace_pipe_placeholder(index)),
        },
        _ => return node.clone(),
    };
    SNode::new(new_node, node.span)
}

#[cfg(test)]
mod tests {
    use super::*;
    use harn_lexer::Lexer;
    use harn_parser::Parser;

    fn compile_source(source: &str) -> Chunk {
        let mut lexer = Lexer::new(source);
        let tokens = lexer.tokenize().unwrap();
        let mut parser = Parser::new(tokens);
        let program = parser.parse().unwrap();
        Compiler::new().compile(&program).unwrap()
    }

    #[test]
    fn test_compile_arithmetic() {
        let chunk = compile_source("pipeline test(task) { let x = 2 + 3 }");
        assert!(!chunk.code.is_empty());
        assert!(chunk.constants.contains(&Constant::Int(2)));
        assert!(chunk.constants.contains(&Constant::Int(3)));
    }

    #[test]
    fn test_compile_function_call() {
        let chunk = compile_source("pipeline test(task) { log(42) }");
        let disasm = chunk.disassemble("test");
        assert!(disasm.contains("CALL"));
    }

    #[test]
    fn test_compile_if_else() {
        let chunk =
            compile_source(r#"pipeline test(task) { if true { log("yes") } else { log("no") } }"#);
        let disasm = chunk.disassemble("test");
        assert!(disasm.contains("JUMP_IF_FALSE"));
        assert!(disasm.contains("JUMP"));
    }

    #[test]
    fn test_compile_while() {
        let chunk = compile_source("pipeline test(task) { var i = 0\n while i < 5 { i = i + 1 } }");
        let disasm = chunk.disassemble("test");
        assert!(disasm.contains("JUMP_IF_FALSE"));
        assert!(disasm.contains("JUMP"));
    }

    #[test]
    fn test_compile_closure() {
        let chunk = compile_source("pipeline test(task) { let f = { x -> x * 2 } }");
        assert!(!chunk.functions.is_empty());
        assert_eq!(chunk.functions[0].params, vec!["x"]);
    }

    #[test]
    fn test_compile_list() {
        let chunk = compile_source("pipeline test(task) { let a = [1, 2, 3] }");
        let disasm = chunk.disassemble("test");
        assert!(disasm.contains("BUILD_LIST"));
    }

    #[test]
    fn test_compile_dict() {
        let chunk = compile_source(r#"pipeline test(task) { let d = {name: "test"} }"#);
        let disasm = chunk.disassemble("test");
        assert!(disasm.contains("BUILD_DICT"));
    }

    #[test]
    fn test_disassemble() {
        let chunk = compile_source("pipeline test(task) { log(2 + 3) }");
        let disasm = chunk.disassemble("test");
        assert!(disasm.contains("CONSTANT"));
        assert!(disasm.contains("ADD"));
        assert!(disasm.contains("CALL"));
    }
}