style(rl): F1.3 code review fixes — comments + spec annotations

Code-quality review found 1 Important + 4 Minor; applied all 5:
- I1: restored `(issue #9, drift-free)` cross-link in Phase 4 header
- M1: added explicit launch profile in header `Grid=(1,1,1), Block=(1,1,1), smem=0`
- M2: comment explaining `count` reuse in Phase 3 (Welford state retained in registers)
- M3: inline rationale for `kelly == 0.0f` and `cooldown == 0.0f` exact equality
- M4: extended Welford-bootstrap comment with statistical floor justification
       (exempt from ISV-promotion per "physics/math constants" rule)

Zero functional change — comments only; cubin rebuilds identical bytes.

crates/ml-alpha/cuda/rl_regime_observer.cu

@@ -8,6 +8,8 @@
 // Per feedback_no_atomicadd: single-thread single-block, no atomics.
 // Per feedback_cpu_is_read_only: pure device kernel.
 // Per feedback_nvidia_grade_perf_for_kernels: no host branches in capture.
+//
+// Launch: Grid=(1,1,1), Block=(1,1,1), smem=0.
 
 // ─── ISV slot indices (mirror Rust constants from isv_slots.rs) ─────
 #define RL_KELLY_FRACTION_INDEX                  676
@@ -39,6 +41,10 @@ extern "C" __global__ void rl_regime_observer(
     if (threadIdx.x != 0 || blockIdx.x != 0) return;
 
     // ─── Phase 1: dead-zone detection ──────────────────────
+    // kelly==0.0f: analytic Kelly clamp writes exactly 0.0 when fraction ≤ 0
+    //   (see rl_kelly_fraction_controller). Exact equality is the intended test.
+    // cooldown==0.0f: integer-valued step counter stored as float; exact 0 is
+    //   the only safe comparison point.
     const float kelly        = isv[RL_KELLY_FRACTION_INDEX];           // prior-step value
     const float cooldown     = isv[RL_COOLDOWN_REMAINING_STEPS_INDEX];
     const int   flat_count   = flat_count_d[0];
@@ -84,11 +90,15 @@ extern "C" __global__ void rl_regime_observer(
     }
 
     // ─── Phase 3: tail-event detection (3σ threshold) ──────
+    // `count` is intentionally reused below from Phase 2 (in-register value
+    // post-conditional-increment); no re-read from ISV needed.
     const float var       = isv[RL_REGIME_SESSION_PNL_VARIANCE_EMA_INDEX];
     const float sigma_thr = isv[RL_REGIME_TAIL_SIGMA_THRESHOLD_INDEX];
     const float sigma     = sqrtf(var);
 
-    // Require count >= 10 before tail detection (Welford bootstrap)
+    // Require count >= 10 before tail detection. Statistical floor — Welford
+    // sample variance is undefined for N<2 and noisy for N<10; exempt from
+    // ISV-promotion per "physics/math constants" rule.
     const int sufficient_count = (count >= 10.0f) ? 1 : 0;
     const int is_tail = sufficient_count && (sigma > 0.0f) && (fabsf(dx) > sigma_thr * sigma);
 
@@ -96,7 +106,7 @@ extern "C" __global__ void rl_regime_observer(
     if (is_tail) recency = 0.0f; else recency += 1.0f;
     isv[RL_REGIME_TAIL_EVENT_RECENCY_INDEX] = recency;
 
-    // ─── Phase 4: emit recovery_factor and eps_recovery_live (drift-free) ──
+    // ─── Phase 4: emit recovery_factor and eps_recovery_live (issue #9, drift-free) ──
     const float n_recovery = isv[RL_KELLY_EPS_RECOVERY_N_RECOVERY_INDEX];
     const float eps_min    = isv[RL_KELLY_EPS_RECOVERY_MIN_INDEX];
     const float eps_max    = isv[RL_KELLY_EPS_RECOVERY_MAX_INDEX];