How do I debug boajs itself?

[sevenc-nanashi]

I was trying to embed MathJax to Rust application using BoaJS, but I got this panic, that looks like internal error of BoaJS:

Details

[2026-04-19T15:03:29Z INFO  render_arg] Rendering TeX: f(x)=e\\g(x)=\pi^100

thread 'mathjax-svg-rs' (770878) panicked at /home/sevenc7c/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/boa_engine-0.21.1/src/vm/opcode/define/mod.rs:
82:33:
index out of bounds: the len is 0 but the index is 1
stack backtrace:
   0: __rustc::rust_begin_unwind
             at /rustc/59807616e1fa2540724bfbac14d7976d7e4a3860/library/std/src/panicking.rs:689:5
   1: core::panicking::panic_fmt
             at /rustc/59807616e1fa2540724bfbac14d7976d7e4a3860/library/core/src/panicking.rs:80:14
   2: core::panicking::panic_bounds_check
             at /rustc/59807616e1fa2540724bfbac14d7976d7e4a3860/library/core/src/panicking.rs:271:5
   3: <usize as core::slice::index::SliceIndex<[T]>>::index_mut
             at /home/sevenc7c/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/slice/index.rs:278:14
   4: core::slice::index::<impl core::ops::index::IndexMut<I> for [T]>::index_mut
             at /home/sevenc7c/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/slice/index.rs:31:15
   5: <alloc::vec::Vec<T,A> as core::ops::index::IndexMut<I>>::index_mut
             at /home/sevenc7c/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/vec/mod.rs:3812:9
   6: boa_engine::environments::runtime::declarative::PoisonableEnvironment::set
             at /home/sevenc7c/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/boa_engine-0.21.1/src/environments/runtime/declarative/mod.rs:310:35
   7: boa_engine::environments::runtime::declarative::function::FunctionEnvironment::set
             at /home/sevenc7c/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/boa_engine-0.21.1/src/environments/runtime/declarative/function.rs:66:20
   8: boa_engine::environments::runtime::declarative::DeclarativeEnvironmentKind::set
             at /home/sevenc7c/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/boa_engine-0.21.1/src/environments/runtime/declarative/mod.rs:200:44
   9: boa_engine::environments::runtime::declarative::DeclarativeEnvironment::set
             at /home/sevenc7c/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/boa_engine-0.21.1/src/environments/runtime/declarative/mod.rs:80:19
  10: boa_engine::environments::runtime::EnvironmentStack::put_lexical_value
             at /home/sevenc7c/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/boa_engine-0.21.1/src/environments/runtime/mod.rs:280:13
  11: boa_engine::vm::opcode::define::PutLexicalValue::operation
             at /home/sevenc7c/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/boa_engine-0.21.1/src/vm/opcode/define/mod.rs:82:33
  12: boa_engine::vm::opcode::handle_put_lexical_value
             at /home/sevenc7c/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/boa_engine-0.21.1/src/vm/opcode/mod.rs:313:17
  13: boa_engine::vm::opcode::<impl boa_engine::context::Context>::execute_bytecode_instruction
             at /home/sevenc7c/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/boa_engine-0.21.1/src/vm/opcode/mod.rs:464:9
  14: core::ops::function::FnOnce::call_once
             at /home/sevenc7c/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/ops/function.rs:250:5
  15: boa_engine::vm::<impl boa_engine::context::Context>::execute_instruction
             at /home/sevenc7c/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/boa_engine-0.21.1/src/vm/mod.rs:649:9
  16: boa_engine::vm::<impl boa_engine::context::Context>::execute_one
             at /home/sevenc7c/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/boa_engine-0.21.1/src/vm/mod.rs:674:14
  17: boa_engine::vm::<impl boa_engine::context::Context>::run
             at /home/sevenc7c/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/boa_engine-0.21.1/src/vm/mod.rs:858:24
  18: boa_engine::script::Script::evaluate
             at /home/sevenc7c/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/boa_engine-0.21.1/src/script.rs:172:30
  19: boa_engine::context::Context::eval
             at /home/sevenc7c/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/boa_engine-0.21.1/src/context/mod.rs:200:41
  20: mathjax_svg_rs::Runtime::new
             at /home/sevenc7c/ghq/github.com/sevenc-nanashi/mathjax-svg-rs/src/lib.rs:145:14
  21: mathjax_svg_rs::MathJax::new::{{closure}}
             at /home/sevenc7c/ghq/github.com/sevenc-nanashi/mathjax-svg-rs/src/lib.rs:280:35
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

thread 'main' (770594) panicked at examples/render_arg.rs:64:10:
Failed to render TeX: "MathJax worker thread stopped before rendering finished"
stack backtrace:
   0: __rustc::rust_begin_unwind
             at /rustc/59807616e1fa2540724bfbac14d7976d7e4a3860/library/std/src/panicking.rs:689:5
   1: core::panicking::panic_fmt
             at /rustc/59807616e1fa2540724bfbac14d7976d7e4a3860/library/core/src/panicking.rs:80:14
   2: core::result::unwrap_failed
             at /rustc/59807616e1fa2540724bfbac14d7976d7e4a3860/library/core/src/result.rs:1867:5
   3: core::result::Result<T,E>::expect
             at /home/sevenc7c/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/result.rs:1185:23
   4: render_arg::main
             at /home/sevenc7c/ghq/github.com/sevenc-nanashi/mathjax-svg-rs/examples/render_arg.rs:64:10
   5: core::ops::function::FnOnce::call_once
             at /home/sevenc7c/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/ops/function.rs:250:5
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

So how do I debug boajs itself?

Repo is here: https://github.com/sevenc-nanashi/mathjax-svg-rs/tree/feat/extra-font