P9 complete: compiled kernels validated (byte-identical, 78-80 GSA samples/min/core), scaling report

Graviton3 c7g.8xlarge, 360 GSE165845 arrays: 360/360 GTCs identical between the Rust
kernels and the pure-Python paths; 1 worker 78-80 samples/min (pure Python 29.6).
Scaling 1->8 workers efficiency 0.87-0.90; above that the 125 MB/s gp3 disk caps the
run (~620 samples/min) and, on a RAM disk, a fixed per-worker start-up cost limits a
360-sample batch to efficiency 0.48 at 32 workers (K-025). Worker state is pickled once.
docs/validation/P9.md, result JSONs, guide/README/CHANGELOG updates.

docs/validation/P9_scaling_gp3.json

@@ -0,0 +1,74 @@
+{
+ "samples": 360,
+ "backend": "rust 1.0.0",
+ "cpu_count": 32,
+ "machine": "aarch64",
+ "runs": [
+  {
+   "threads": 1,
+   "rc": 0,
+   "wall_s": 299.1,
+   "setup_s": 6.9,
+   "per_sample_phase_s": 276.63,
+   "samples_per_min": 78.1,
+   "samples_per_min_per_core": 78.1,
+   "speedup_vs_first": 1.0,
+   "efficiency": 1.0
+  },
+  {
+   "threads": 2,
+   "rc": 0,
+   "wall_s": 166.5,
+   "setup_s": 7.1,
+   "per_sample_phase_s": 143.78,
+   "samples_per_min": 150.2,
+   "samples_per_min_per_core": 75.1,
+   "speedup_vs_first": 1.92,
+   "efficiency": 0.96
+  },
+  {
+   "threads": 4,
+   "rc": 0,
+   "wall_s": 96.9,
+   "setup_s": 6.8,
+   "per_sample_phase_s": 74.58,
+   "samples_per_min": 289.6,
+   "samples_per_min_per_core": 72.4,
+   "speedup_vs_first": 3.71,
+   "efficiency": 0.927
+  },
+  {
+   "threads": 8,
+   "rc": 0,
+   "wall_s": 61.9,
+   "setup_s": 6.8,
+   "per_sample_phase_s": 39.56,
+   "samples_per_min": 546.0,
+   "samples_per_min_per_core": 68.3,
+   "speedup_vs_first": 6.99,
+   "efficiency": 0.874
+  },
+  {
+   "threads": 16,
+   "rc": 0,
+   "wall_s": 57.4,
+   "setup_s": 6.9,
+   "per_sample_phase_s": 34.98,
+   "samples_per_min": 617.5,
+   "samples_per_min_per_core": 38.6,
+   "speedup_vs_first": 7.91,
+   "efficiency": 0.494
+  },
+  {
+   "threads": 32,
+   "rc": 0,
+   "wall_s": 57.4,
+   "setup_s": 6.9,
+   "per_sample_phase_s": 34.91,
+   "samples_per_min": 618.8,
+   "samples_per_min_per_core": 19.3,
+   "speedup_vs_first": 7.92,
+   "efficiency": 0.247
+  }
+ ]
+}