feat(alpha): reserve ISV slot block 539..550 for alpha trading system

12 contiguous slots reserved for durable alpha-system infrastructure:
- 539-542: diagnostics (Q-spread, action entropy, return-vs-random,
  early-Q-movement EMAs) — read by Phase E kill criteria
- 543-546: stacker-threshold controller (threshold, target, observed-rate,
  Kelly attenuation) — engagement-rate self-correction
- 547-548: random-uniform baseline (mean, std) — anchor for kill criterion 541
- 549-550: reserved spare (absorb growth without bumping ISV_TOTAL_DIM)

Named `alpha_isv_slots` rather than `phase_e_isv_slots` because these slots
are intended to outlive any individual Phase E/F/G milestone — the SP4..SP22
naming was iteration-scoped, but this block is system-scoped infrastructure.

ISV_TOTAL_DIM bumped to 551. All indices validated in 4 unit tests
(bounds, membership, uniqueness, total-dim coverage). Audit doc
docs/isv-slots.md updated per Invariant-7.

docs/isv-slots.md

@@ -502,3 +502,38 @@ work stream and establishes the slot base for upcoming components:
 **Producers/consumers status:** Pre.2 lands the slot reservation only; Pre.3 registers in state reset machinery; all 10 slots are zero-initialized until subsequent SP20 phases land producers (per-epoch ISV seeds + GPU kernels) and consumer migration. Mirrors the SP4/SP5/SP11/SP15 pre-allocation pattern.
 
 **ISV_TOTAL_DIM:** 510 → 520 (Pre.2 adds 10 slots).
+
+## Alpha trading system — durable infrastructure block (2026-05-15)
+
+Phase E intro commit reserves 12 contiguous slots at `[539..551)` for **system-scoped** infrastructure of the alpha trading stack (stacker / execution-policy diagnostics, controller anchors, population baselines). Unlike the per-iteration SP4..SP22 reservations, this block is named for the *system* — slots are intended to outlive any individual Phase E/F/G milestone. New slots in this range should be added in `alpha_isv_slots.rs` first; spares at 549..550 absorb growth without bumping `ISV_TOTAL_DIM`.
+
+| Index | Name constant                       | Role         | Producer (initial commit)              | Update cadence       | Notes |
+|-------|-------------------------------------|--------------|----------------------------------------|----------------------|-------|
+| 539   | `Q_SPREAD_EMA_INDEX`                | Diagnostic   | (none; Phase E.1 kill-criteria kernel) | per-rollout-step     | `std(Q, axis=action) / |mean(Q)|`; kill-criterion #1 |
+| 540   | `ACTION_ENTROPY_EMA_INDEX`          | Diagnostic   | (none; Phase E.1 kill-criteria kernel) | per-rollout-step     | `H(action_dist)` over recent rollouts; kill-criterion #2 |
+| 541   | `RETURN_VS_RANDOM_EMA_INDEX`        | Diagnostic   | (none; Phase E.1 kill-criteria kernel) | per-trade-close      | `(rollout_R − random_R) / σ_random`; kill-criterion #3 |
+| 542   | `EARLY_Q_MOVEMENT_EMA_INDEX`        | Diagnostic   | (none; Phase E.1 kill-criteria kernel) | per-epoch            | `|Q(s_early) − Q_init|/|Q_init|`; kill-criterion #4 |
+| 543   | `STACKER_THRESHOLD_INDEX`           | Controller   | (none; Phase E.2 stacker controller)   | per-rollout-step     | Confidence threshold for trade eligibility; engagement-rate self-correction |
+| 544   | `TRADE_RATE_TARGET_INDEX`           | Anchor       | host init at training start            | static               | Target trade-rate fraction (e.g. 0.08) |
+| 545   | `TRADE_RATE_OBSERVED_EMA_INDEX`     | Diagnostic   | (none; Phase E.2 stacker controller)   | per-rollout-step     | Observed trade-rate EMA |
+| 546   | `STACKER_KELLY_ATTENUATION_INDEX`   | Controller   | (none; Phase E.2 stacker controller)   | per-trade-close      | Multiplied with `KELLY_F_SMOOTH_INDEX=280` before contract-cap; bounded [0.1, 1.0] per `pearl_blend_formulas_must_have_permanent_floor` |
+| 547   | `RANDOM_BASELINE_MEAN_INDEX`        | Anchor       | host computes once per fold            | per-fold             | Mean reward of uniform-random execution policy at the given horizon |
+| 548   | `RANDOM_BASELINE_STD_INDEX`         | Anchor       | host computes once per fold            | per-fold             | Std of same — used to compute `RETURN_VS_RANDOM_EMA` σ-distance |
+| 549   | (reserved spare)                    | —            | —                                      | —                    | Absorb growth; do not use ad-hoc |
+| 550   | (reserved spare)                    | —            | —                                      | —                    | Absorb growth; do not use ad-hoc |
+
+**Files touched (intro commit, slot reservation only):**
+- `crates/ml/src/cuda_pipeline/alpha_isv_slots.rs` (new) — 10 `pub const *_INDEX` constants + `ALPHA_ISV_BLOCK_LO=539`/`ALPHA_ISV_BLOCK_HI=550` bookends + 4 unit tests (bounds, membership, uniqueness, total-dim coverage)
+- `crates/ml/src/cuda_pipeline/mod.rs` — adds `pub mod alpha_isv_slots;`
+- `crates/ml/src/cuda_pipeline/gpu_dqn_trainer.rs` — `ISV_TOTAL_DIM: 539 → 551`; comment updated to reference `alpha_isv_slots.rs`
+
+**Producers/consumers status:** intro commit is reservation-only. Producers land later in Phase E:
+- Phase E.1: `phase_e_kill_criteria.cu` writes slots 539-542
+- Phase E.2: `stacker_threshold_controller.cu` writes slots 543, 545, 546 (reads 544 as anchor)
+- Phase E.0: host writes 544 (trade-rate target) at training start and 547, 548 (baselines) per fold
+
+State-reset-registry dispatch arms for all 10 active slots land in the immediately-following commit (Phase E Task 2), per `feedback_registry_entries_need_dispatch_arms`.
+
+**Naming rationale:** SP4..SP22 reservations are *milestone-scoped* (a specific SP iteration); this block is *system-scoped* (alpha trading system across Phase E/F/G/...). The naming difference is intentional — future alpha-system additions go in `alpha_isv_slots.rs`, not in a per-phase file.
+
+**ISV_TOTAL_DIM:** 539 → 551 (12 slots reserved, 10 active, 2 spare).