The hold enforcement infrastructure (enforce_hold in trade_physics.cuh,
hold_time counter at ps[10], action masking in experience_action_select)
was already fully implemented but disabled by min_hold_bars defaulting
to 1. Change default from 1 to 5 so hold enforcement is active by
default. Production configs already set min_hold_bars=10 via TOML.
Targets ~100-200K trades instead of 619K across 5M bars.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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