Layer 1: Per-sample CE clamped to MAX_PER_SAMPLE_CE=50 before IS weight.
Breaks PER feedback loop: high loss → high priority → high IS weight → repeat.
Layer 2: Bellman target smoothed with ε=0.01 uniform mix after projection.
Prevents any atom from having zero probability → no log(near-zero) in CE.
Root cause: C51 cross-entropy is unbounded when target and predicted
distributions are maximally misaligned. PER amplifies pathological samples.
These two layers cap the maximum possible CE and prevent the extreme
misalignment from occurring.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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