Function maybe_grow_stack 

pub fn maybe_grow_stack<R>(f: impl FnOnce() -> R) -> R

Grow the stack on demand to prevent overflow in deeply nested ASTs.

This is called by generated FromNode implementations at every recursive call site. When the remaining stack space drops below the red-zone (32 KiB), a new 1 MiB stack segment is allocated transparently. The overhead on the happy path (enough stack left) is a single pointer comparison.