feat(sp14/sp22): enlarge aux head + trunk capacity (8x head, 2x trunk-H2)
After Path C confirmed aux head's 28% accuracy at H=60 is the H6 Phase 3
bottleneck (not the mechanism itself), enlarge aux capacity:
- AUX_HIDDEN_DIM: 32 -> 256 (8x, matches input dim, removes bottleneck)
- AUX_TRUNK_H2: 128 -> 256 (2x, uniform trunk width)
Architecture changes:
- Aux head: 256 -> Linear -> 256 -> ELU -> Linear -> 2 (was 256->32->2)
- Aux trunk: 256 -> 256 -> 256 -> 256 (was 256 -> 256 -> 128 -> 256)
- +160K params total (mostly aux_nb_w1 + aux_rg_w1: [256, 256] each)
Side effects:
- Checkpoint fingerprint change (intentional)
- Thread utilisation improves: AUX_BLOCK=256 threads x H=256 = 1:1
(vs 8:1 at H=32 — most threads idle previously)
Phase 3 mechanism stays DORMANT (W=0, beta=0) for this validation
smoke. Verdict criteria: aux_dir_acc improves from 0.28 toward 0.50+
with the larger capacity. If yes, re-activate Phase 3 priors. If no,
the bottleneck is signal/horizon, not capacity.
Cargo build clean (full nvcc rebuild).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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