\section{The K12 Lookahead Bug}
\label{sec:the-bug}

% TODO content notes (fill in once audit/input/ is populated and audited):
% - Identify the exact line(s) in backtester.py responsible for the leak.
% - Show a minimal before/after diff.
% - Explain mechanically why the genetic algorithm search (Iter12, 15
%   hyperparameters) was able to find and exploit this leak: GA optimizes
%   whatever signal is available, including backtest-mechanics artifacts: if
%   the fitness function rewards future-peeking, the search converges on
%   parameters that maximize the exploit, not real predictive skill.
% - Quantify the leak's effect size on the original (real BTCUSDT) data:
%   Sharpe under the bug vs Sharpe under time_machine.py (the honest engine),
%   same hyperparameters, same data.
% - This section depends on the forensic files under audit/input/code/ —
%   do not fill in specifics until that audit is complete (see MANIFEST.md
%   for the exact commit hash and dataset hash being audited).