The plan asks for a separate `hold_cost_scale_compute_kernel.cu` to
host the two-sided multiplicative ramp 1.05/0.95 controller for
`HOLD_COST_SCALE_INDEX = 513`. Reality: the controller is already
implemented inside Phase 1.3's `sp20_controllers_compute_kernel.cu`
lines 175-194 (block 6 of the 6-controller fused kernel) and tested
end-to-end at `sp20_controllers_compute_test::hold_cost_scale_two_
sided_ramp` covering all 5 cases (ramp up, ramp down, deadband, upper-
clamp, lower-clamp).
Splitting it back into a separate kernel would:
1. Break the in-thread `tgt` reuse optimization documented in the
fused kernel header (sp20_controllers_compute_kernel.cu:73-78);
forces 1 extra ISV read per step.
2. Add separate launch + cubin + Rust launcher boilerplate for
~20 LoC of kernel logic.
3. Force the production caller (gpu_experience_collector.rs:6549)
to make TWO controller-kernel launches per step.
Per `feedback_no_partial_refactor` ("when a contract changes, every
consumer migrates atomically") + `feedback_no_quickfixes`, the
correct response is errata, not a partial-refactor split.
This commit also documents 4 additional Phase 3 plan-vs-reality gaps
that emerged during implementation review (Gaps 8-11):
- Gap 8: Task 3.3's target_hold_pct controller is already wired in
Phase 1.3 + has a unit test; Task 3.3 commit will add a behavioral
integration test, NO production code changes.
- Gap 9: hold_baseline_buffer layout is `[N_envs, 30]` row-major
(per-env), NOT a single global ring as the spec phrasing implied
— the kernel is per-env-parallel and per-trade attribution
requires per-env stride.
- Gap 10: `PS_ENTRY_BAR` does NOT exist; `PS_HOLD_TIME` (slot 10) +
`segment_hold_time` (already in scope at trade close) suffice.
No new state slot needed — keeps PS_STRIDE = 43 contract stable.
- Gap 11: Task 3.4 plan refers to `GpuBatchPtrs` but that struct
is in `crates/ml-dqn/src/gpu_replay_buffer.rs`. The collector
struct is `GpuExperienceBatch`. Both need the new `aux_conf`
field + the ring-buffer scatter/gather column in between.
Plan-level errata only; no code touched in this commit. Implementation
of the actual Phase 3 work continues in Tasks 3.2 / 3.3 / 3.4.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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