is_budget_exceeded() used `0 === $budget` but floatval() returns float,
so 0 (int) === 0.0 (float) is always false. This caused unlimited
budget ($0) to be treated as exceeded, blocking all AI generation.
Same bug existed in the admin display (showed "$0.00" instead of
"Unlimited" for budget remaining).
This was a P1 bug that prevented ALL AI content generation since v4.3.0.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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