bench: jetson FPS battery — both backends saturate at 80.9 MB scale

Parameterizes the throttle-sweep FPS battery (fpsBattery helper) and adds a
jetson-agx-thor run: asyncify raf 2.1-5.3 / distinct 0.2-0.8 vs JSPI raf
1.9-5.0 / distinct 0.1-0.7 — indistinguishable. Suspension overhead is a
per-event-loop-turn cost; at hundreds of ms of GAL work per frame it stops
discriminating. vme-wren (~27 MB) remains the discriminating size class.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016X9eh1s5sTx1o9Em9KBuwR

docs/features/async/migration-evidence/jspi-vs-asyncify-bench-2026-08.md

@@ -156,6 +156,16 @@ The distinct-frame gap grows from +21 % at 1× to +68 % at 4× — the same
 "advantage widens under throttle" signature doc-12 used to prove lower
 CPU-per-operation (as opposed to just a smaller module).
 
+**FPS on jetson-agx-thor (80.9 MB)** — added 2026-08-14 pm: at this scale BOTH
+arms saturate outright and the backend difference disappears into noise
+(asyncify raf 2.1–5.3 / distinct 0.2–0.8; JSPI raf 1.9–5.0 / distinct
+0.1–0.7; post-FPS heap 1.90 vs 1.73 GB). With <1 real redraw/s the 6 s
+windows count 1–5 frames, i.e. quantization noise. Reading: suspension
+overhead is a per-event-loop-turn cost — once per-frame GAL/geometry work is
+hundreds of ms, it no longer discriminates. vme-wren (~27 MB) is the size
+class where the backend visibly matters for interaction; jetson is the
+"both need render-side optimization" regime.
+
 **Memory checkpoints** (wasm linear memory; Chromium `usedJSHeapSize` tracked
 alongside, differences <10 %): boot 557 vs 387 MB; after vme-wren open 962 vs
 802 MB; unchanged after the FPS sweep on both arms.