cleanup(cuda): Fix 30 Ambiguous-A — delete orphan phantom_liquidity_gbm

Closes Fix 29 audit row #18. The synthetic-data overlay kernel
`phantom_liquidity_gbm` in `dqn_utility_kernels.cu:1050-1096` was
flagged ❓ Ambiguous because its writer wrote `log_ret` to
`market_features[bar*market_dim + 0]` and `+3` — the WRITER's
downstream consumer contract was unverifiable post Bug 1 (commit
`5a5dd0fed`) which redefined feature index 0 from raw log-return to
z-normed log-return.

Investigation result: zero callers in the entire codebase. The audit
grep `grep -rn "phantom_liquidity_gbm" crates/ml/src/ services/
crates/ bin/` returns ONLY the kernel definition itself — no
`load_function`, no `launch_builder`, no Rust-side launcher. The
kernel has been compiled but never invoked since at least early 2026.

Resolution: delete the kernel definition and replace with an
explanatory comment block. Per `feedback_no_hiding` an orphan kernel
with an ambiguous post-Bug-1 contract is exactly the failure mode the
rule warns against — a future re-wirer would have written
synthetic z-normed log-returns into a slot the production pipeline
expects raw log-returns at, re-introducing the very Bug-1 drift the
audit was triaging. Per `feedback_wire_everything_up` a kernel that
compiles but is unconsumed is either wired in the same commit or
deleted; this kernel was never wired since its writer existed.

The replacement comment block (23 lines) documents the design intent
(GBM-based synthetic-data augmentation) so any future re-introduction
has the spec available, plus the re-introduction conditions:
caller wiring must land in the same commit, and the writer/consumer
contract for `market_features[..+0]` (z-normed vs raw log-return)
must be explicit at the kernel boundary.

What this change touches:
  - crates/ml/src/cuda_pipeline/dqn_utility_kernels.cu:1037-1096
    47-line kernel definition + ══ comment header deleted; 23-line
    DELETED notice replaces it. Net -24 lines.
  - docs/dqn-wire-up-audit.md
    Fix 30 Ambiguous-A row appended with the dead-code-deleted
    resolution. Stale-B deferral note also added (separate paragraph)
    documenting the pre-existing `_via_pinned` guard block requires a
    dedicated `gpu_backtest_evaluator.rs` migration commit before the
    Stale-B kernel-side fix can land.

Verification:
  - SQLX_OFFLINE=true cargo build -p ml --release --offline
    --features cuda (1m 30s) clean; cubin recompiled via nvcc.
  - Pre-commit guards pass.
  - Final grep for `phantom_liquidity_gbm` returns only the comment
    block in the kernel file.

Refs Fix 29 row #18 deferred follow-up. `feedback_no_hiding`
(delete orphans, do not leave them as ambiguous landmines),
`feedback_wire_everything_up` (every module/feature/kernel built
must be wired to a production path or removed),
`feedback_no_functionality_removal` does NOT apply: a kernel with
zero callers is not a functional feature, and the audit doc retains
the design intent so any future re-introduction can rebuild the
mechanism with the correct post-Bug-1 contract.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/dqn-wire-up-audit.md

@@ -3816,6 +3816,7 @@ Closes the four ⚠ Stale and one ❓ Ambiguous sites Fix 29 enumerated. Each si
 | 14 | `crates/ml/src/trainers/dqn/trainer/metrics.rs:576` (`val_data → window_prices`) | ⚠ Stale — reads `target[0]` (preproc_close, z-normed log-return) as a dollar close price | Switched to `target[TARGET_RAW_CLOSE]` (col 2). Dead `fv[3]` fallback deleted (`set_val_data_from_slices` always yields `target.len() == 6` post `TARGET_DIM=6` bump in `063fd2716`, so the fallback is unreachable; per `feedback_no_hiding` deleted rather than left as a silent wrong-units fallback). Imports `TARGET_RAW_CLOSE` from `crate::fxcache`. | ✅ |
 | 15 | `crates/ml/src/hyperopt/adapters/dqn.rs:2492` (`val_close_prices`) | ⚠ Stale — same `target[0]` / `fv[3]` pattern as #14 in the HPO val backtest path | Same fix shape as #14: `target[TARGET_RAW_CLOSE]`, dead fallback deleted, named constant import. Affects HPO val Sharpe + window aggregation. | ✅ |
 | 12 | `crates/ml/src/cuda_pipeline/scripted_policy_kernel.cu:59-65` (seed-phase MOMENTUM / MEAN_REV / VWAP_DEV `recent_ret`) | ⚠ Stale — reads `state[MARKET_START]` (z-normed log-return post Bug 1) as `close_now`, then computes `(close_now − prev_close) / prev_close` where `prev_close` is raw_close. Mixed units made `recent_ret` meaningless; seed-phase MOMENTUM/MEAN_REV/VWAP_DEV branches degenerated to noise-floor below the ±0.0001f cutoffs | Kernel signature extended with `const float* targets`, `const int* episode_starts`, `int t`, `int total_bars`. Per-thread `bar_idx = episode_starts[i] + t`, then `close_now = targets[bar_idx*6 + TARGET_RAW_CLOSE]` matching env_step's source (`experience_kernels.cu:1769`). Bounds-clamp to `[0, total_bars-1]` mirrors env_step's out-of-bounds early-return. The previous `bar_idx` parameter (per-step `t` mixed into the LCG seed) renamed `t`; the LCG seed now mixes per-thread `bar_idx = episode_starts[i] + t` instead — stronger entropy across episodes, no behavioural regression (UNIFORM policy still produces a 4-direction uniform distribution). Single launcher (`gpu_experience_collector.rs:3735`) migrated in the same commit; `total_bars` already in scope from line 3301. Recent_ret signal preserved per `feedback_no_functionality_removal`; the audit's CUSUM-substitution alternative path explicitly rejected (the recent_ret signal is the seed-policy contract, not the implementation accident). NO new `PS_*` slot or PORTFOLIO_STRIDE bump required — the targets buffer is the canonical raw_close source and routing it directly avoids cascading through ~12 PS_STRIDE consumers. | ✅ |
+| 18 | `crates/ml/src/cuda_pipeline/dqn_utility_kernels.cu:1050-1096` (`phantom_liquidity_gbm` synthetic-feature overlay) | ❓ Ambiguous — writes `log_ret` to `market_features[bar*market_dim + 0]` and `+3` for synthetic GBM episodes; downstream consumer contract unverifiable | Investigation: `grep -rn "phantom_liquidity_gbm" crates/ml/src/ services/ crates/ bin/` returns ZERO callers — no `load_function`, no `launch_builder`, no Rust-side launcher. Kernel is dead code. Per `feedback_no_hiding` + `feedback_wire_everything_up`: deleted the kernel definition; replaced with a 23-line explanatory comment block documenting why (no consumer existed, contract unverifiable, hypothetical re-wire would have introduced exactly the Bug-1 contract drift the audit was triaging). Re-introducing GBM-overlay augmentation must land caller wiring in the same commit per `feedback_wire_everything_up`. | ✅ |
 
 **Stale-A commit** (rows #14, #15):
 - `crates/ml/src/trainers/dqn/trainer/metrics.rs` — column-index swap + import + dead-fallback deletion + comment.
@@ -3830,3 +3831,11 @@ References: clones the host-side variant of Fix 27 Bug B exactly. `feedback_no_h
 - `docs/dqn-wire-up-audit.md` — Stale-C row appended.
 
 References: Stale-C restores seed-phase scripted policy quality (post-seed all branches use the network's Q-spread, so the affected blast radius is bounded to the warm-start window — `replay_seed_steps` = 100k production / 1k smoke). `feedback_no_partial_refactor` (single launcher migrates with the kernel signature change in one commit), `feedback_no_functionality_removal` (recent_ret signal stays — only its data source is fixed; CUSUM substitution explicitly rejected per the audit's contract-decision branch), `feedback_no_hiding` (no fallback to z-normed-log-return reads remaining; the kernel either gets real raw_close or clamps to total_bars-1 boundary), `feedback_no_cpu_compute_strict` n/a (zero new host-side compute; targets buffer already exists at line 3042), `feedback_no_htod_htoh_only_mapped_pinned` already satisfied (`targets_buf` is mapped pinned by upstream caller).
+
+**Ambiguous-A commit** (row #18):
+- `crates/ml/src/cuda_pipeline/dqn_utility_kernels.cu` — `phantom_liquidity_gbm` kernel definition (47 lines including its `══` comment header) deleted; replaced with a 23-line `/* ... DELETED ... */` block citing the audit grep result, the Bug-1 contract trap, and the re-introduction conditions per `feedback_wire_everything_up`.
+- `docs/dqn-wire-up-audit.md` — Ambiguous-A row appended with the dead-code-deleted resolution.
+
+References: this is the dead-code branch of the contract decision. The kernel had been live in the codebase since at least early 2026 with no consumer ever materialising. `feedback_no_hiding` (orphan kernels with ambiguous contracts get deleted, not left for a future contributor to re-wire wrong), `feedback_wire_everything_up` (an orphan kernel that compiles but is unconsumed is exactly the failure mode this rule prevents — wire it in the same commit or delete it). `feedback_no_functionality_removal` does NOT apply: a kernel with zero callers is not a functional feature, and the audit doc retains the design intent (synthetic-data augmentation via GBM) so any future re-introduction has the spec available.
+
+**Stale-B (row #13) — DEFERRED**: pre-existing `clone_to_device_*_via_pinned` guard violations in `gpu_backtest_evaluator.rs` (5 sites at lines 641-650, 1468) block any commit that stages this file. The DtoD-via-pinned guard landed today (commit `5275932f4`) and the file has not been migrated since the guard landed; this would be the first commit to do so. Migration scope is 5 buffer allocations + 3 launch-site updates (CudaSlice → MappedF32Buffer + `.dev_ptr` indirections) covering buffers (`prices_buf`, `features_buf`, `window_lens_buf`, `portfolio_buf`, plus the `reset_evaluation_state` portfolio re-init) that are orthogonal to Bug-1 contract drift. Per `feedback_no_partial_refactor` the right unit-of-work is a single dedicated commit migrating all 5 sites at once, not folding the migration under the Stale-B header. The Stale-B kernel-side fix (route `prices_buf` to `backtest_plan_state_isv` and read `prices[base+3]` instead of `features[base+0]`) is stashed at `stash@{0}` (`stale-b-wip`) for re-application after the `_via_pinned` migration lands. Affects val plan_isv slots [PNL_VS_TARGET], [PNL_VS_STOP] only — gradient flow on the main training graph is unaffected (Fix 29 `Summary` line confirms).