First half of Phase B4b (replay-buffer label scatter chain). Amends
the Phase A2 trade_outcome_label_kernel to emit a per-(env, t) output
column alongside the existing per-env tile, and adds the collector-side
buffer + per-step launch arg.
Kernel amendment (trade_outcome_label_kernel.cu):
- Added NULL-tolerant `out_labels_per_sample` arg after existing
`out_labels`. When non-NULL, writes
`out_labels_per_sample[env*L + t] = label` at the same offset as
the `trade_close_per_sample[env*L + t]` read. NULL = no-op
(preserves Phase A2/A3 contract for callers passing old signature).
- Pattern mirrors the K=2 head's `aux_sign_labels` per-(i, t) ring
column that threads through the replay buffer.
Collector field + alloc + launch:
- New struct field `exp_aux_to_label_per_sample: CudaSlice<i32>`
sized `[alloc_episodes × alloc_timesteps]`. Sentinel -1 (mask)
populated by alloc_zeros + per-step kernel writes — survives
until a trade-close event overwrites the env's slot at that t.
- Updated Phase B3 launcher in collect_experiences_gpu to pass
`self.exp_aux_to_label_per_sample.raw_ptr()` as the new arg.
Why split B4b into B4b-1 + B4b-2: the full replay-buffer wireup
mirrors the K=2 head's aux_sign_labels pattern across ~8 distinct
code sites (replay-buffer struct field, sample destination buffer,
direct-to-trainer pointer, setter method, scatter on insert, gather
direct, gather fallback, GpuBatchPtrs field). Splitting lets us
validate the per-(i, t) producer in isolation before touching the
consumer pipeline.
B4b-1 (this commit) = producer chain complete. Per-(env, t) column
populated correctly every rollout step. Consumer wiring (replay-
buffer scatter + trainer setter) is B4b-2's scope.
Verification:
- cargo check -p ml clean (21 warnings, none new).
- cargo test -p ml --lib → 1016/0 on clean runs; pre-existing
test_dqn_checkpoint_round_trip NoisyLinear flake still surfaces
~50-70% of full-suite runs (flake predates Phase B4b, unrelated
to trade-outcome head — disable_noise() zeros ε but leaves some
other randomness source intact).
Audit: docs/dqn-wire-up-audit.md Phase B4b-1 section.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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