Closes out Wave 4.1 (Phase 1.5.b consumer migration). Wave 4.1a (a8da1cb9c)
landed bn_tanh_concat_dd_kernel that fuses dd_pct into the trunk input;
Wave 4.1b (eb9515e41) wired s1_input_dim 102→103 through GRN reshape + 4
forward + 3 backward call sites. Wave 4.1c proves the wiring actually
changes the policy: a synthetic GPU forward composing launch_sp15_bn_concat_dd
with cublasSgemm_v2 against random Xavier-init weights W[proj_h=4, 103]
yields measurably different action distributions when ISV[DD_PCT]=0.0 vs
0.10 — observed mean KL=1.158e-4 (max=3.005e-4) vs threshold 1e-6
(~100× headroom).
Why a synthetic projection vs the real GRN trunk: the seeded forward_trunk_for_test
helper from Wave 4.1a noted (lines 2304-2319) that exposing the trainer's
trunk forward for tests would require either (a) a public surface change on
DQNTrainer exposing internal cuBLAS handles + GRN scratch + weights (the
trainer's fused_ctx is pub(crate) and only initialised inside the training
loop at training_loop.rs:547 — DQNTrainer::new returns with fused_ctx: None),
or (b) duplicating the trunk's cuBLAS setup in a test (≥200 lines of buffer
plumbing). Both options are architecturally heavier than the test's purpose
justifies. Per the spec dispatch ("the test's purpose is 'non-zero KL proves
the wire is connected' not 'verifies trained behavior'"), the synthetic
single-layer projection is the right scope: it exercises the new column-102
weights on the dd_pct value — exactly the path the real GRN's Linear_a first
GEMM takes for w_a_h_s1[:, 102] (the dd_pct column added by Wave 4.1b's
reshape).
Test contract:
- Two passes through launch_sp15_bn_concat_dd + cublasSgemm_v2 differ ONLY in
ISV[DD_PCT_INDEX=406] (0.0 at-ATH vs 0.10 in-DD).
- Inputs (bn_hidden, states) deterministic; weights deterministic via LCG
seed=42 with Xavier-uniform bound = sqrt(6 / (103+4)) ≈ 0.237.
- KL > 1e-6 (set 100× below the observed magnitude so a real wiring break
fires this test, not silently passing).
What this test does NOT verify: the full GRN composition (ELU/GLU/LN/residual)
propagating dd_pct through h_s2 + the branch advantage heads. That end-to-end
behavior is exercised by the L40S smoke + production training runs.
Phase 1.5.b orphan launcher chain fully eliminated per
feedback_wire_everything_up: kernel landed (4.1a) → consumer migration
(4.1b) → behavioral verification (4.1c) — three atomic commits, the
3a/3b/3c split-pattern matching Wave 3's a/b decomposition. The Wave 4.1a
transient orphan window opened in a8da1cb9c → closed in eb9515e41 →
behavioral coverage added here.
Wave 4.1a's seeded helpers consumed: kl_divergence (used) and
minimal_trainer_for_tests (retained but unused — the seeded comment
correctly identified that exposing the trunk forward via the trainer
surface is non-trivial, so the helper waits for a future cargo-cult test
that needs trainer construction without GPU forward, e.g. weight-shape
introspection).
Touched: crates/ml/tests/sp15_phase1_oracle_tests.rs (+1 module
sp15_wave_4_1c_behavioral with 1 ignored test, 2 helper fns, 1 assertion
block — purely additive, no kernel or production-code changes), docs/dqn-wire-up-audit.md
(Wave 4.1c entry at top of audit doc).
Verified:
- SQLX_OFFLINE=true cargo check -p ml --features cuda --tests clean (18
pre-existing unrelated warnings, no new warnings).
- CUDA_COMPUTE_CAP=86 cargo test -p ml --test sp15_phase1_oracle_tests
--features cuda -- --ignored bn_concat dd_pct --nocapture: 2 of 2 oracle
tests green (Wave 4.1a bn_tanh_concat_dd_kernel_writes_dd_pct_column +
Wave 4.1c dd_pct_trunk_input_shifts_policy_distribution).
- cargo test -p ml --features cuda --lib: 947 passed / 12 failed —
exactly matches Wave 4.1b baseline (test addition is in the --test
integration target, not lib target).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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