Stored raw_reward alongside scaled reward in Transition. At sample
time, consumer re-applies current reward_scale to raw_reward instead
of using the stale-scale stored reward. This eliminates off-policy
scale drift that caused q_pi_agree to collapse from 0.125 to 1e-22
over 40k steps with PER=32768.
PER capacity set to 16384 (1024 unique steps at b=16) — balances
replay depth against h_t representation staleness.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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