feat(bb/msm): headless WebGPU-only MSM autorun + static build for real-device runs

[AztecBot]

WebGPU MSM + base-field diagnostics & timing on real devices (BrowserStack), without the WASM/COI path, plus a static build so the page loads on a phone.

Autorun modes (?autorun= / mobile-safe ?cfg=<base64(JSON)>)

• msm-webgpu — one WebGPU MSM (random [kᵢ]G points by default).
• msm-diag — per-stage diagnostics. MsmV2.runStaged() submits each kernel separately (canary readback per stage → device-loss attribution); collectDiagnostics() digests every stage buffer for M2-vs-S25 comparison; posts host scalar/point digests + device.lost.
• msm-sweep — WebGPU MSM timing sweep logn_min..logn_max, median of reps, per size; skips MsmV2's all-0x01 warm-up (which collapses every point into one bucket → a maximally deep single-submit pair-tree that trips a mobile GPU's watchdog) and warms with the real inputs.
• bench-field-verify — 1M montmul/fr_add/fr_sub vs JS BigInt.
• ?cfg=<base64> packs all params into one truncation-safe value (BrowserStack mobile workers drop everything after the first &).

Findings (BrowserStack, identical seeded input via cfg)

• Field primitives bit-exact on M2 and S25 (montmul/add/sub, 1,048,576 each, 0 mismatches).
• MSM compute is correct on the S25: per-stage, every stage buffer hashes identically M2==S25 (incl. bucketResult, redBuf); the only difference, valIdx_scatter, is benign atomic-ordering (bucket sums are order-independent).
• Timing sweep (median ms, random points, seed=1):

log₂N	M2 (M2 macOS Chrome)	S25 (Android, Snapdragon)
10	12.8	3340.9 (hang/recover)
11	13.9	value is not invertible
12	15.6	—
13	19.6	—
14	26.9	—
15	38.5	—
16	53.4	—
17	104.6	—
18	171.6	—

M2 runs the whole batched MSM cleanly across all sizes. The S25 cannot run the batched single-submit run() reliably — it hangs/recovers (3.3 s at 2^10) or corrupts the result (value is not invertible at 2^11), even though its per-stage execution is correct. The defect is the large single command buffer on the Adreno/Dawn-Vulkan path (VK_ERROR_DEVICE_LOST / watchdog), not the algorithm.

• iPhone: still not reachable via BrowserStack /5/worker JS-Testing.

Run it

cd barretenberg/ts && yarn install
node_modules/.bin/vite build --config dev/msm-webgpu/vite.build.config.ts
node dev/msm-webgpu/scripts/serve-static.mjs --port 5199
# tunnel 5199; on the device (single mobile-safe cfg param):
#   <tunnel>/dev/msm-webgpu/index.html?cfg=<base64({"autorun":"msm-sweep","logn_min":10,"logn_max":18,"reps":3,"scalar_seed":1})>

dist/ is gitignored.