CRIT (gpt-5.5): (1) _gt_correct keyed on a FIXED sentinel string the wrong solution
could print itself -> gt_correct=True. Now a fresh secrets.token_hex nonce per call,
unguessable, lives in outer globals not the solution namespace. (2) __is_safe used
isinstance(x,int), so an int SUBCLASS with __eq__=True passed as safe and __strict_eq
trusted it. Now exact types (type(x) in (...)). +2 verify cases (forge_sentinel,
int-subclass eq). 29/29.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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