Plan C Phase 2 T6. Adds an #[ignore]-gated GPU test that exercises
the production experience_action_select kernel directly through a
minimum-viable inline cudarc fixture (ProdActionSelectFixture). The
Plan B audit fixture (GpuExperienceCollector::new_for_test) was never
built, so each test in this Phase 2 batch builds its own buffers,
launches the kernel, and reads back action picks for assertions.
Setup mirrors Phase 0 Test 0.D failure-mode:
- Flat/Hold C51 logits = peaked at v=0 atom (δ(v=0) shape)
- Long/Short C51 logits = log-Gaussian centred at v=-0.001, σ=0.05
- Linear adaptive support [v_min=-0.5, v_max=+0.5, delta_z=0.05]
- Uniform q_values (mag/ord/urg fall through Boltzmann uniformly)
Assertions:
- Eval mode (eps=0): 10 launches at distinct timesteps produce
IDENTICAL per-sample dir_idx (deterministic argmax E[Q]).
Every sample picks Hold or Flat (E[Q] argmax bias reproduces).
- Training mode (eps_start=0.5): >=30% of 10 000 samples pick
Long or Short (Thompson explores directional alternatives).
Shared helpers (PROD_B0..3, decode_dir/mag/ord/urg, fill_peaked_logits,
fill_linear_support, ProdActionSelectFixture) added at the top of the
Phase 2 section to be reused by Tests 2.B-2.D.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
212651c943