wifi-densepose/docs/adr/ADR-163-edge-latency-measurement.md

ADR-163: Edge-Latency Measurement — CLAIMED budgets → MEASURED-on-host

• Status: accepted
• Date: 2026-06-12
• Deciders: ruv
• Tags: edge-latency, wasm-edge, esp32, cog-inference, criterion, prove-everything, measurement-debt
• Amends: ADR-160 (deferred "criterion benches for process_frame budget claims" line now DONE-on-host); ADR-159 (cog inference latency)

Context — Milestone 9 of the beyond-SOTA sweep

Prior milestones (M5/M6, ADR-159/ADR-160) flagged measurement debt: edge latency budgets asserted in doc-comments and manifests but never reproduced by a committed benchmark. Specifically:

• Many wifi-densepose-wasm-edge skill modules document a timing budget "on ESP32-S3 WASM3" (e.g. exo_time_crystal: "H (heavy, <10 ms)"). These were CLAIMED, not benchmarked. ADR-160's deferred backlog named exactly this: "Criterion benches for process_frame budget claims — ACCEPTED-FUTURE."
• cog-pose-estimation's manifest cites cold_start_ms_avg: 5.4, but neither cog had a benches/ directory or any committed inference-latency number.

Under the project's prove-everything / anti-"AI-slop" directive, a CLAIMED latency budget that a skeptic cannot reproduce is debt. M9 pays it down — benches and docs only, no production-code behavior change (so nothing republishes).

Headline

Converted the CLAIMED edge-latency budgets into MEASURED-on-host numbers, with the honest host-vs-ESP32 caveat stated everywhere. Added committed criterion benches over the heaviest hot paths and a results file a skeptic can re-run. The ESP32-on-hardware figure remains explicitly UNMEASURED — this milestone does not pretend a laptop reproduces an Xtensa/WASM3 budget.

Decision — benches landed

T1 — wasm-edge process_frame budget benches

v2/crates/wifi-densepose-wasm-edge/benches/process_frame_bench.rs (criterion, harness = false, required-features = ["std"]). The crate is excluded from the v2 workspace, so it runs from the crate dir. Benches the M6-audit-named heaviest hot paths over a fixed synthetic CSI frame, each driven through the public process_frame after warming the relevant ring/phase buffers so the expensive path actually executes:

• exo_time_crystal::process_frame — full 256-pt × 128-lag autocorrelation.
• exo_ghost_hunter::process_frame — empty-room periodicity / hidden-breathing.
• sec_weapon_detect::process_frame — per-subcarrier (MAX_SC=32) Welford.
• med_seizure_detect::process_frame — clonic-rhythm path (#[cfg(feature = "medical-experimental")], only built/run with that gate).

The lib's bench = false was set so the libtest harness does not intercept criterion CLI flags; the ghost_hunter bin is already standalone-bin-gated and not built under --features std.

Measured host medians (Intel Core Ultra 9 285H, native --release): exo_time_crystal 17.3 µs · exo_ghost_hunter 1.44 µs · sec_weapon_detect 0.42 µs · med_seizure_detect 0.10 µs.

T2 — cog inference latency benches

v2/crates/cog-person-count/benches/infer_bench.rs and v2/crates/cog-pose-estimation/benches/infer_bench.rs (criterion, harness = false). Each loads the real shipped weights from the in-repo cog/artifacts/, asserts the Candle CPU backend (so the stub can never be silently benched), warms one forward, then times steady-state InferenceEngine::infer over a fixed CSI window on Device::Cpu.

Measured host medians: cog-person-count 305 µs · cog-pose-estimation 305 µs (steady-state, CPU, real weights).

T3 — results file

benchmarks/edge-latency/RESULTS.md, in the benchmarks/wiflow-std/RESULTS.md style: each number with its exact reproduce command, the machine, the MEASURED-on-host grade, and the honest caveat.

The honest caveat (recorded, non-negotiable)

1. Host ≠ ESP32. The wasm-edge benches run native x86_64, not Xtensa/WASM3. A host median is an upper bound on algorithm work, not the ESP32 number; WASM3 interpretation on a ~240 MHz core is 1–2 orders of magnitude slower than native -O. A host median under budget does not prove the ESP32 meets it. The ESP32 figure is NOT reproduced here — it needs hardware.
2. Bench ≠ the doc-claimed measurement. The cogs' manifest cites a cold-start number (weight-load included); these benches measure steady-state per-frame infer. We report both, labelled, and do not conflate them. Empirically, pose steady-state (305 µs host) is ~18× under the 5.4 ms cold-start — the expected shape, and exactly why conflating would lie.

Deferred / still-pending (nothing dropped)

• ESP32-on-hardware process_frame latency — PENDING (hardware). Needs the wasm32-unknown-unknown target built + flashed to an ESP32-S3 and timed under WASM3. The host bench is the algorithm-cost proxy until then.
• Per-skill accuracy remains DATA-GATED (unchanged from ADR-160) — this ADR measures latency only, never claims detection accuracy.

Reproduction (MEASURED)

# T1 — wasm-edge (workspace-excluded → run from the crate dir)
cd v2/crates/wifi-densepose-wasm-edge
cargo bench --features std -- --warm-up-time 1 --measurement-time 2
cargo bench --features std,medical-experimental -- --warm-up-time 1 --measurement-time 2 med_seizure

# T2 — cogs (workspace members)
cd v2
cargo bench -p cog-person-count   --no-default-features --bench infer_bench
cargo bench -p cog-pose-estimation --no-default-features --bench infer_bench

# existing tests still green (behavior unchanged)
cargo test -p cog-person-count -p cog-pose-estimation --no-default-features

Consequences

• ADR-160's deferred "Criterion benches for process_frame budget claims" line is now DONE (host); the ESP32-on-hardware confirmation is explicitly the one remaining pending item.
• The cogs now ship committed, reproducible steady-state inference-latency numbers, cleanly distinguished from the manifest's cold-start claim.
• No runtime behavior changed; no crate republishes. PROOF.md's performance table and scripts/prove.sh's gated section reference the new benches.