Function max_parse_recursion 

pub fn max_parse_recursion() -> usize

The parse-time recursion budget: an EIGHTH of the AST limit (min the floor).

The parser’s own descent is BY FAR the fattest stack consumer — each parenthesis level re-enters the whole precedence/condition chain — so it gets a much tighter budget than the built-tree limit. The number that matters is the ratio between one level’s frame and the smallest stack the parser must survive on:

measured	value
one level of descent, debug build (2026-09)	~64 KiB
smallest stack the gate is tested on	2 MiB
levels before the real stack dies	32
this budget at the default limit	16

The budget must fire BEFORE the stack dies, or the guard is decorative: a SIGABRT is exactly the crash it exists to prevent. It was a QUARTER of the limit, which put it at 32 — the cliff itself, with no margin — so any growth of the descent’s frame turned a graceful rejection into a stack overflow, and one did. An eighth spends half the stack instead of all of it, which is room for the parser to keep growing.

Still scales with LOGOS_MAX_AST_DEPTH: raising it asserts a deeper stack, and raises both together as before.