Derived from JackHsieh/6059z0it-chunk-records-only-val
for the cognitive_classifier sanity checks. Positive control: prefixes and
documents are UNCHANGED (real data throughout). For every item labeled
"helped" (log_prob_mean_diff >= 0 under bin_edges=[0.0]), exactly
1 random position(s) of THAT ITEM's OWN thought tokens
(never the prefix) are overwritten with the single token ' Pikachu'
(id 96919 in the Qwen/Qwen3-4B-Base… See the full description on the dataset page:
https://huggingface.co/datasets/JackHsieh/6059z0it-chunk-records-only-val-pikachu.
