Adds a paired diagnostic to localise the eval-mode collapse mechanism.
The existing `val_dir_dist` line reads `actions_history_buf` which env_step
overwrites with the POST-physics `actual_dir` (signed position bucket). When
the policy picks Long but the Kelly cap zeroes target_position, the bar shows
up as `actual_dir=Flat` — indistinguishable in the existing diagnostic from a
case where the kernel itself produced a Flat pick.
Cluster runs `ddrpr` (without Kelly fix) and `txdz9` (with Kelly fix
2c97e0436) produced bit-identical val_dir_dist patterns — Boltzmann math
should give `P(best) ≤ 47.5%` and `P(any direction) ≥ 13.5%` for 4 actions
with `tau=q_range`, yet observed `P(Long) + P(Short) ≈ 0.0007`. One of
those bounds is being violated and the existing diagnostic can't tell which.
The new `val_picked_dir_dist` reads `chunked_actions_buf` — the kernel's
RAW Boltzmann action_idx output BEFORE env_step computes actual_dir.
Divergence between the two distributions answers the gating question:
- both flat → kernel itself produces collapsed picks (Q-values degenerate)
- val_picked diverse, val_dir_dist flat → env_step drains to Flat
(Kelly / margin / trail stop)
Sample is the most recent chunk (~64 bars on 1-window val). Noisier than
the full-window post-physics histogram but enough for qualitative
comparison against Boltzmann theory bounds.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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