Lands the plan-conditioning concat kernel for the K=3 trade-outcome
forward as reusable scaffolding. Phase B5b (integration) is deferred
with rationale: Phase C (state slots) is more critical for testing the
K=3 head's effect on policy behavior, and can land independently of
the plan-conditioning refinement.
NEW kernel aux_to_input_concat_kernel.cu:
- Writes [B, SH2+P] from h_s2_aux [B, 256] || plan_params [B, 6]
- Pure GPU map; one thread per output element, no atomicAdd
- NULL-tolerant on plan_params (zeros trailing P cols when source
unavailable, e.g., collector cold-start where the trade plan head
doesn't run)
- Registered in build.rs; cubin compiles (5.7 KB). Dead code at this
commit — no Rust launcher yet.
Why B5 is split + B5b deferred:
Full Phase B5 (integration) requires three coordinated changes:
1. Forward path: bump aux_to_fwd.forward() to SH2=262 + 262-dim input
2. Backward stride mismatch: backward emits dh_s2_aux_to_buf [B, 262],
but dh_s2_aux_accum (input to aux trunk backward) is [B, 256]. A
direct SAXPY mismatches row strides (262 vs 256) and corrupts the
trunk's upstream gradient. Needs a strided-SAXPY kernel.
3. Collector-path plan_params unavailability: trade plan head only runs
trainer-side. Workarounds: zero-fill, add trade plan to collector,
or skip K=3 forward in collector. All have trade-offs.
Phase B5b would need (1) strided-SAXPY kernel and (2) collector
plan_params decision. Real work but NOT on the critical path for
testing the K=3 head's effect on WR.
Why Phase C should land first:
The K=3 head currently trains on real labels (post-B4b) but doesn't
influence policy behavior. Phase C wires the head's softmax into state
slots [121..124) = (p_Profit, p_Stop, p_Timeout), replacing the K=2
single-slot 121 = 2*p_up - 1. WITH Phase C the policy reads aux's
outcome predictions as state features → behavior changes → testable.
Without Phase C, validation runs would show "K=3 head trains and
converges" but predictions don't reach the policy → WR signal isn't
a function of K=3 at all. We'd be testing nothing.
Recommendation: skip the full B5 for now, do Phase C next, then Phase
D (atom-shift). Phase B5b (plan-conditioning) is a refinement we add
IF Phase C/D's no-plan-params version shows promise but plateaus
below the WR ≥ 0.55 target.
Audit: docs/dqn-wire-up-audit.md Phase B5a section.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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