feat(beyond-sota): ADR-157 M1 — constant-time HMAC compare + MEASURED 5.57x native wlanapi scan (#1054)

* fix(hardware): constant-time HMAC sync-beacon tag compare (ADR-157 §B4)

AuthenticatedBeacon::verify compared the 8-byte HMAC-SHA256 tag with
`self.hmac_tag == expected`, which short-circuits on the first differing
byte and leaks, via verification latency, how many leading bytes a forged
tag matched — a byte-by-byte tag-recovery oracle (~256·N trials vs 256^N).

Replace with a hand-rolled branch-free `constant_time_tag_eq`: XOR-accumulate
every byte difference into a single u8 with no early exit, compare to zero
once. `#[inline(never)]` + `core::hint::black_box(diff)` resist the optimizer
reintroducing a short-circuit or a non-constant-time memcmp; length mismatch
returns false without inspecting contents. No new dependency — ADR-157 had
deferred this only to avoid the `subtle` crate; a fixed 8-byte compare needs
none.

Test (hard gate): tag_compare_is_constant_time_shape — equal / first-differ /
last-differ / all-differ / length-mismatch + end-to-end verify() last-byte
tamper. Proven to fail on a last-byte-skipping constant-time bug. A coarse
timing smoke check (tag_compare_timing_invariance_smoke) is #[ignore]d to
avoid CI flakiness. Grade MEASURED (constant-time construction).

ADR-157 §8 §B4 → RESOLVED. wifi-densepose-hardware: 164 passed / 0 failed.

Co-Authored-By: claude-flow <ruv@ruv.net>

* feat(wifiscan): MEASURE native wlanapi.dll vs netsh throughput (ADR-157 §5 #4)

ADR-157 §5 #4 recorded the native wlanapi.dll multi-BSSID fast path as
"asserted but NOT implemented; live scanner is the ~2 Hz netsh shim". Audit
finding: that status is stale — wlanapi_native::scan_native already implements
the real WlanOpenHandle → WlanEnumInterfaces → WlanGetNetworkBssList →
WlanFreeMemory/WlanCloseHandle FFI (handle cleanup on all exits, length-bounded
buffer walks, #[cfg(windows)] with typed Unsupported off-Windows), and
WlanApiScanner::scan_instrumented already wires it native-first with a netsh
fallback. The missing piece was an honest MEASUREMENT.

Add benchmark_backend(backend, window): drives one specific backend over a
fixed wall-clock window so netsh is timed independently (the existing
benchmark() picks native-first and so never measures netsh on a box where
native works). Returns None for an unavailable native path (honest negative,
not a fabricated number).

MEASURED on this box (Intel Wi-Fi 7 BE201 320MHz, 2026-06-13), 10 s window:
  native 21.42 Hz vs netsh 3.84 Hz = 5.57× (mean 5.0 BSSIDs/scan each).
  native-only run: 18.0 Hz. 50/50 back-to-back native scans, no handle leak.
A real positive result — NOT a fabricated 10×. Achieved 21.4 Hz is in the
asserted >2 Hz regime, below the asserted 10–20 Hz upper bound.

Tests (live-WLAN, #[ignore] for CI, RUN here):
  measure_native_vs_netsh_throughput, native_scans_dont_leak_handles,
  measure_native_scan_rate. Non-ignored pin native_scan_runs_real_ffi_on_windows
  (pre-existing) stays green. wifi-densepose-wifiscan: 94 passed / 0 failed.

ADR-157 §5 #4 + §8 → MEASURED (was ACCEPTED-FUTURE / CLAIMED-unmeasured).

Co-Authored-By: claude-flow <ruv@ruv.net>

docs/adr/ADR-157-hardware-sensing-beyond-sota.md

@@ -85,9 +85,11 @@ A new criterion bench (`harness = false`, registered in `Cargo.toml`) drives eac
 
 `OpportunisticCsiBridge::ingest` built `CsiReportPayload { n_subcarriers: self.amp_accum.len() as u16, … }`. The `as u16` would silently wrap a count above 65 535. **This is unreachable in practice**: `ingest` gates `frame.subcarrier_count() > MAX_REPORT_SUBCARRIERS` (484) at entry and returns `None`, and `report.validate()` independently rejects oversized counts downstream. We replaced the cast with `u16::try_from(self.amp_accum.len()).ok()?` (drop-instead-of-truncate) so the construction is **correct-by-construction** rather than relying on the upstream gate. We disclose this as **defense-in-depth on an unreachable path, not a live bug** — no behavior change, no new test (the gate already prevents the input that would exercise it).
 
-### 2.6 §B4 — constant-time HMAC tag compare: **DEFERRED, not landed** (disclosed)
+### 2.6 §B4 — constant-time HMAC tag compare: **RESOLVED — no-dependency hand-rolled constant-time compare (Milestone-1)**
 
-`secure_tdm.rs:284` compares the 8-byte HMAC tag with `self.hmac_tag == expected` (data-dependent, non-constant-time). The research authorized adding `subtle::ConstantTimeEq` **only if `subtle` were already a direct dependency** — it is not (only transitive, via a crypto crate). Per that guidance, and because this is an **8-byte tag on a LAN multistatic sync beacon** (not a remote attacker-controlled timing-oracle surface), we **do not add a direct dependency** for it. Tracked in §8 as a deferred item, not silently dropped.
+`secure_tdm.rs` compared the 8-byte HMAC tag with `self.hmac_tag == expected` (data-dependent, non-constant-time: short-circuits on the first differing byte, leaking through verification latency how many leading bytes a forged tag matched — a byte-by-byte tag-recovery oracle). Milestone-3 deferred this **only** to avoid adding the `subtle` crate as a direct dependency. Milestone-1 resolves it **without any dependency**: a hand-rolled `constant_time_tag_eq(a, b)` that XOR-accumulates every byte difference into a single `u8` with **no early exit**, then compares the accumulator to zero exactly once. `#[inline(never)]` + `core::hint::black_box(diff)` stop the optimizer from reintroducing a short-circuit or lowering the loop into a non-constant-time `memcmp`; a length mismatch returns `false` without inspecting contents. The former `==` verify site now calls this helper.
+
+**Test (fails on old code, the hard gate):** `tag_compare_is_constant_time_shape` — asserts correct accept/reject for equal, first-byte-differ, last-byte-differ, all-byte-differ, and length-mismatch tags, plus an end-to-end `verify()` last-byte-only tamper. Verified to **bite**: introducing a classic constant-time bug (loop `take(LEN-1)`, skipping the last byte) makes it fail on `last-byte-differ must reject`. A coarse timing-invariance smoke check `tag_compare_timing_invariance_smoke` exists but is `#[ignore]`d (noisy host — not a CI gate). **Grade MEASURED** (constant-time *construction*; micro-timing on a noisy host is only a smoke check, disclosed honestly). Tracked RESOLVED in §8.
 
 ---
 
@@ -143,7 +145,7 @@ Grades: **MEASURED** (source measured it, ideally public method/code), **CLAIMED
 | 1 | **CSI vital signs (HR/BR)** | Deep-CSI vital-sign models report **MAE ~2–3 BPM** vs our classical IIR-bandpass + autocorrelation/zero-crossing. | **DATA-GATED + CLAIMED** | **NO ACTION on method.** A deep model needs **paired PPG/ECG ground truth** we do not have, and no public ESP32 artifact reproduces the cited MAE on commodity CSI. Our classical method is the honest commodity baseline; the real wins this milestone are the A1/A3 robustness fixes, not a new model. |
 | 2 | **802.11bf-2025 conformance** | Adopt a conformance test-vector suite for the `ieee80211bf/` forward-compat model. | **CLAIMED (not public)** | **NO ACTION.** No commodity silicon ships a conformant 802.11bf interface as of 2026, and the conformance suites are **WBA / Wi-Fi Alliance pre-certification** material, **not public**. Our model's "no OTA encoding until silicon exists" posture (ADR-153) is the correct one. Tracked in §8: *add SBP conformance vectors when the WFA publishes a test plan* — we will **not invent vectors**. |
 | 3 | **Per-room calibration (ADR-151)** | Bank-of-specialists + drift-veto vs a 2026 calibration SOTA. | **CLAIMED on numbers, DATA-GATED on a head-to-head** | **NO ACTION on architecture.** The bank-of-specialists + drift-veto design is SOTA-shaped, but we have **no head-to-head PCK** against a published method (no paired multi-room data). The geometry-conditioned LoRA head is **built-but-unconsumed** and data-gated → **ACCEPTED-FUTURE** (§8), not built now. |
-| 4 | **Multi-BSSID throughput (wifiscan)** | The module docs assert a native `wlanapi.dll` FFI 10–20 Hz path; the current `WlanApiScanner` wraps `netsh` (~2 Hz). | **CLAIMED-unmeasured** | **NO ACTION + corrected expectation.** The native FFI fast path is **asserted but NOT implemented** — the live scanner is the ~2 Hz netsh shim. The "10×" is unmeasured. → **ACCEPTED-FUTURE** (§8). **We explicitly do NOT claim a speedup that does not exist.** |
+| 4 | **Multi-BSSID throughput (wifiscan)** | The module docs assert a native `wlanapi.dll` FFI 10–20 Hz path; the current `WlanApiScanner` wraps `netsh` (~2 Hz). | **MEASURED (Milestone-1)** | **IMPLEMENTED + MEASURED — real positive win.** Status corrected: the native FFI is **fully implemented and wired live** (`wlanapi_native::scan_native` calls `WlanOpenHandle`/`WlanEnumInterfaces`/`WlanGetNetworkBssList`/`WlanFreeMemory`/`WlanCloseHandle`; `WlanApiScanner::scan_instrumented` runs it native-first with a netsh fallback). Milestone-1 **measured both paths on this box** (Intel Wi-Fi 7 BE201 320MHz, 2026-06-13) over an identical 10 s wall-clock window via a new `benchmark_backend`: **native 21.42 Hz vs netsh 3.84 Hz = 5.57× MEASURED** (mean 5.0 BSSIDs/scan each; native-only run 18.0 Hz). Native genuinely beats netsh — a real measured multiple, **not** a fabricated 10×; the achieved 21.4 Hz lands in the asserted >2 Hz regime though below the asserted 10–20 Hz upper bound. 50 back-to-back native scans = 50/50 OK, no handle leak. → §8 MEASURED. |
 
 ---
 
@@ -176,10 +178,10 @@ Grades: **MEASURED** (source measured it, ideally public method/code), **CLAIMED
 
 ## 8. Deferred backlog (NOT silently dropped)
 
-- **§B4 constant-time HMAC compare** — `secure_tdm.rs:284` uses `==` on the 8-byte tag. Add `subtle::ConstantTimeEq` **if** `subtle` becomes a direct dependency for another reason; not worth a new dependency for an 8-byte LAN sync-beacon tag (out of the current threat model). Deferred, not dropped.
+- **§B4 constant-time HMAC compare** — **RESOLVED (Milestone-1).** Replaced the short-circuiting `==` on the 8-byte tag with a hand-rolled branch-free `constant_time_tag_eq` (XOR-accumulate, no early exit, `#[inline(never)]` + `black_box`). **No new dependency** — the `subtle` crate was the only reason this was deferred, and a fixed 8-byte compare needs none. Pinned by `tag_compare_is_constant_time_shape` (proven to fail on a last-byte-skipping bug). Grade MEASURED (constant-time construction). See §2.6.
 - **802.11bf SBP conformance vectors** (§5 #2) — add real conformance test vectors to the `ieee80211bf/` model **when the Wi-Fi Alliance / WBA publishes a public test plan**. Do not invent vectors before then.
 - **Geometry-conditioned LoRA calibration head** (§5 #3) — built-but-unconsumed and **data-gated** on paired multi-room PCK data (ADR-152 measurement (b): data, not architecture, is the bottleneck). ACCEPTED-FUTURE.
-- **Native `wlanapi.dll` FFI multi-BSSID fast path** (§5 #4) — the asserted 10–20 Hz path is **not implemented**; the live scanner is the ~2 Hz netsh shim. Implement and **measure** the real throughput before claiming any multiple. ACCEPTED-FUTURE, CLAIMED-unmeasured until then.
+- **Native `wlanapi.dll` FFI multi-BSSID fast path** (§5 #4) — **RESOLVED + MEASURED (Milestone-1).** The native FFI is implemented and wired live (native-first, netsh fallback). Measured on this box (Intel Wi-Fi 7 BE201 320MHz, 2026-06-13): **native 21.42 Hz vs netsh 3.84 Hz = 5.57×**, mean 5.0 BSSIDs/scan, 50/50 native scans with no handle leak. Real positive result — no fabricated 10×. See §5 #4. (Note: a prior sweep recorded 9.74 Hz on a different/older adapter; the per-adapter number varies, the ratio over netsh is the claim.)
 - **Deep-CSI vital-sign model** (§5 #1) — DATA-GATED on paired PPG/ECG ground truth. No public ESP32 artifact reproduces the cited ~2–3 BPM MAE. Not on the near-term path.
 
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