Function max_ast_depth 

pub fn max_ast_depth() -> usize

The EFFECTIVE depth limit: DEFAULT_MAX_AST_DEPTH unless the LOGOS_MAX_AST_DEPTH environment variable overrides it.

The default is sized for the tightest standard environment; machines with deep stacks (a big ulimit -s / RUST_MIN_STACK) can raise it, and constrained embedders can lower it — no rebuild required. Read once per process.