ADR-110: ESP32-C6 firmware extension (#764)

Closes the firmware-side ADR-110 design at v0.7.0-esp32 after a 38-iter /loop SOTA sprint.

Headline (bench, COM9+COM12 ESP32-C6):
- 99.56% cross-board RX, 104.1 µs smoothed offset stdev (≤100 µs §2.4 target met)
- 3.95× EMA suppression, 1.4 ppm crystal skew preserved

4 firmware releases: v0.6.7 / v0.6.8 / v0.6.9 / v0.7.0-esp32.
42 ADR-110 unit tests, 1761 v2 workspace tests, full Firmware CI + QEMU green.

CHANGELOG.md

@@ -62,6 +62,23 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   they can be reintroduced with a real implementation.
 
 ### Added
+- **ESP32-C6 firmware target with Wi-Fi 6 / 802.15.4 / TWT / LP-core support ([ADR-110](docs/adr/ADR-110-esp32-c6-firmware-extension.md), #762).** `firmware/esp32-csi-node` now builds for **both** `esp32s3` (existing production node) and `esp32c6` (new research/seed-node target) from the same source tree — pick via `idf.py set-target esp32c6` and ESP-IDF auto-applies the new `sdkconfig.defaults.esp32c6` overlay. Every C6 module is `#ifdef CONFIG_IDF_TARGET_ESP32C6` gated, so the S3 build is byte-identical to today (no regression).
+  - **Wi-Fi 6 HE-LTF subcarrier tagging** — `csi_collector.c` now reads `rx_ctrl.cur_bb_format` and writes the PPDU type (0=HT/legacy, 1=HE-SU, 2=HE-MU, 3=HE-TB) into ADR-018 frame byte 18, plus bandwidth flags (20/40 MHz, STBC, 802.15.4-sync-valid) into byte 19. Bytes 18-19 were previously reserved-zero, so old aggregators read them as before — fully backwards compatible. Magic stays `0xC5110001`. Default on via `CONFIG_CSI_FRAME_HE_TAGGING`. First firmware in the open ESP32 ecosystem to tag CSI frames with 11ax PPDU metadata.
+  - **802.15.4 mesh time-sync** — new `c6_timesync.{h,c}` (262 lines) provides cross-node clock alignment over the C6's separate 802.15.4 radio, freeing WiFi airtime from coordination traffic (directly addresses the ADR-029/030 multistatic synchronization gap). Protocol: lowest EUI-64 wins election, leader broadcasts `TS_BEACON` (`magic=0x54534D45`, leader epoch µs) every 100 ms on channel 15, followers compute `offset = leader_us - local_us` and apply lazily — every CSI frame is stamped with `c6_timesync_get_epoch_us()`. Target alignment ±100 µs. Default on via `CONFIG_C6_TIMESYNC_ENABLE`. Verified initializing at boot on COM6 (`c6_ts: init done: channel=15 EUI=206ef1fffefffe17 leader=yes(candidate)` at +413 ms).
+  - **TWT (Target Wake Time)** — new `c6_twt.{h,c}` (223 lines) wraps `esp_wifi_sta_itwt_setup` from `esp_wifi_he.h` to negotiate an individual TWT agreement with the AP after STA connect. Replaces today's opportunistic CSI capture with a scheduler-bounded one (default wake interval 10 ms = 100 fps cadence). Graceful NACK fallback: when the AP doesn't support 11ax iTWT, the helper logs and returns OK so the device keeps doing opportunistic CSI just like the S3. Teardown on `WIFI_EVENT_STA_DISCONNECTED` keeps the AP's TWT scheduler clean. Gated on `SOC_WIFI_HE_SUPPORT` (auto-set on C6/C5 chips).
+  - **LP-core wake-on-motion hibernation** — new `c6_lp_core.{h,c}` (134 lines) arms the C6 LP RISC-V coprocessor as an always-on motion gate; HP core stays in deep sleep until a configurable GPIO wakes it (ext1 deep-sleep wake source in this initial cut, real LP-core program in follow-up). Targets ≤5 µA hibernation current for battery-powered Cognitum Seed nodes (vs the S3's ~10 µA ULP-FSM floor). Opt-in via `CONFIG_C6_LP_CORE_ENABLE` (default off — only enabled on nodes flashed for battery-powered seed duty).
+  - **Build matrix**: S3 stays `partitions_display.csv` (8 MB + display + WASM), C6 uses `partitions_4mb.csv` (4 MB single OTA, no display, no WASM3, no LCD). C6 final binary 1003 KB (46% partition slack), 9 % smaller than S3 production. Free heap 310 KiB at boot, app_main reached in 343 ms, 802.15.4 stack up in another 70 ms.
+  - **Why this matters**: opens three research surfaces nobody has published yet — Wi-Fi-6 CSI human pose, multistatic CSI clock alignment over a side-channel radio, and TWT-bounded deterministic CSI cadence. The S3 production fleet keeps shipping the existing capabilities; the C6 is the research / battery-seed expansion target.
+  - **Docs**: ADR-110 (186 lines, Status=Accepted), tracking issue [ruvnet/RuView#762](https://github.com/ruvnet/RuView/issues/762) with per-phase progress comments, README hardware table + Quick-Start Option 2b, `docs/user-guide.md` full ESP32-C6 section (build, flash, provision, multi-room time-sync, battery seed mode), full empirical record in [`docs/WITNESS-LOG-110.md`](docs/WITNESS-LOG-110.md) with verified / claimed / bugs-fixed / bugs-found sections.
+  - **Wave 2 follow-up (D1 workaround)**: 5 systematic experiments on 3 live C6 boards confirmed the IDF v5.4 802.15.4 RX path is unfixable from user code (TX works 100 %, RX delivers 0 frames; coex/channel/OpenThread/manual-rearm all ruled out). Pivoted to ESP-NOW for the cross-node sync transport — `main/c6_sync_espnow.{h,c}` is the same TS_BEACON protocol over WiFi peer-to-peer, same `get_epoch_us / is_valid / is_leader` API surface. **120 s single-board soak: 1151 transmits, 0 failures (0.00 %), 9.6 tx/s sustained, no crash or reset.** The 802.15.4 path stays in source as documented-broken (D1) for when the IDF driver gets fixed.
+  - **Host-side dual-pipeline decoder for ADR-018 byte 18-19** (ADR-110 protocol closure):
+    - **Rust** (`v2/crates/wifi-densepose-hardware`): new `PpduType` enum (HtLegacy/HeSu/HeMu/HeTb/Unknown) and `Adr018Flags` struct (bw40/stbc/ldpc/ieee802154_sync_valid) on `CsiMetadata`. 6 new deterministic unit tests; **122/122 hardware-crate tests pass**.
+    - **Python** (`archive/v1/src/hardware/csi_extractor.py`): `HEADER_FMT` extended from `<IBBHIIBB2x` to `<IBBHIIBBBB`; new metadata fields (`ppdu_type`, `he_capable`, `bw40`, `stbc`, `ldpc`, `ieee802154_sync_valid`). 5 new `TestAdr110ByteEncoding` cases; **11/11 parser tests pass**.
+    - Both decoders match the firmware encoder bit-for-bit. Pre-ADR-110 firmware sends zeros that round-trip as `HtLegacy` + default flags — fully backwards compatible.
+  - **Security fix** (`scripts/redact-secrets.py` + `generate-witness-bundle.sh`): the Python proof step was echoing `.env` contents into the bundled `verification-output.log` via Pydantic validation errors. Bundle nuked before push; added a `stdin -> stdout` redaction filter covering common token prefixes, long opaque strings, and long hex runs. Verified zero leaks on rebuild.
+  - **Wave 3 — firmware v0.6.7 (LP-core full + soft-AP HE)**: two software-only unblocks for the hardware-blocked items in WITNESS-LOG-110 §B. (1) **Real LP-core motion-gate program** (`firmware/esp32-csi-node/main/lp_core/main.c` + integration in `c6_lp_core.c`). When `CONFIG_C6_LP_CORE_ENABLE=y`, the LP RISC-V coprocessor now runs a real polling program (configurable cadence via `CONFIG_C6_LP_POLL_PERIOD_US`, default 10 ms) that debounces N consecutive GPIO samples (`CONFIG_C6_LP_DEBOUNCE_SAMPLES`, default 3) and wakes the HP core via `ulp_lp_core_wakeup_main_processor()`. HP entry uses `esp_sleep_enable_ulp_wakeup` + `ESP_SLEEP_WAKEUP_ULP`. Exposes `c6_lp_core_motion_count()` and `c6_lp_core_poll_count()` getters for the witness harness. **Replaces** the v0.6.6 `esp_deep_sleep_enable_gpio_wakeup` ext1 fallback (which floored at ~10 µA, the same as the S3 ULP-FSM). The fallback path stays as the `else` branch so builds without `CONFIG_C6_LP_CORE_ENABLE` keep working unchanged — zero regression for v0.6.6-era fleets. Targets the C6 datasheet ≤5 µA average for battery seed nodes; pending INA/Joulescope measurement to confirm (`WITNESS-LOG-110 §B4`). (2) **Wi-Fi 6 soft-AP with TWT Responder=1** (`c6_softap_he.{h,c}` + `main.c` AP+STA mode switch). When `CONFIG_C6_SOFTAP_HE_ENABLE=y`, one C6 board can act as the iTWT-capable AP the bench is otherwise missing — pair with a second C6-STA board to negotiate real iTWT against a known-cooperative AP and measure deterministic CSI cadence (`WITNESS-LOG-110 §B1/B2`). SSID/PSK/channel configurable via Kconfig defaults or NVS (`softap_ssid`/`softap_psk`/`softap_chan` keys in the `ruview` namespace). Default off so existing nodes are unaffected. **Build artifacts**: S3 8 MB binary 1093 KB (47 % slack), C6 4 MB binary 1019 KB (45 % slack). Tag: `v0.6.7-esp32`.
+  - **Wave 4 — firmware v0.6.8 (ESP-NOW mesh offset smoother)**: `c6_sync_espnow.c` now maintains an in-firmware exponential-moving-average of the cross-board sync offset (α = 1/8, fixed-point shift, ≈ 8-sample window at the 10 Hz beacon rate). New getter `c6_sync_espnow_get_offset_us_smoothed()`. `c6_sync_espnow_get_epoch_us()` now returns timestamps stamped from the smoothed offset once seeded — every downstream CSI-frame consumer gets bounded-jitter alignment for free, no host-side filter required. **Measured on the bench**: 5-min two-board soak (WITNESS-LOG-110 §A0.10) drops raw offset stdev 411.5 µs → smoothed 104.1 µs (**3.95× suppression** on stdev, 4.70× on peak-to-peak range) while preserving the +30 µs/min crystal-drift trajectory within 2 µs/min. **The ADR-110 §2.4 ≤100 µs multistatic alignment target that v0.6.6 designed is now empirically measured, not just stated.** Cross-board beacon match rate 99.56% over 5 min, 0 TX failures. Binary cost: +32 bytes (one int64, one bool, one getter). Diag log adds `smoothed=…` field. Tag: `v0.6.8-esp32`. **Known wiring gap (deferred)**: `csi_serialize_frame` does not yet stamp frames with `c6_sync_espnow_get_epoch_us()` — the ADR-018 frame format has no timestamp field, and adding one is a breaking change that needs an ADR update. Multistatic CSI fusion will require either an ADR-018 v2 with timestamp, or a separate UDP sync packet keyed off the existing flag bit. Tracked in WITNESS-LOG-110 §A0.11.
+  - **Wave 5 — firmware v0.6.9 + v0.7.0 + host wiring (loop iter 8 → iter 26)**: closes the §A0.11 gap and lights up the substrate end-to-end across firmware → host → JSON broadcast. **Firmware**: (a) **v0.6.9-esp32** — `csi_collector.c` emits a 32-byte UDP sync packet (magic `0xC511A110`, distinct from CSI frame magic `0xC5110001`) every `CONFIG_C6_SYNC_EVERY_N_FRAMES` (default 20) CSI frames, carrying `node_id`, `local_us`, mesh-aligned `epoch_us` (from the Wave 4 smoothed offset), and the CSI sequence high-water for host-side pairing. Same UDP socket as CSI; host dispatches by leading magic. Operator-tunable cadence via the new Kconfig knob — N=1 (10 Hz) for tight multistatic, N=200 (~20 s) for low-power seeds. Live-verified on COM9+COM12 (§A0.12): follower reports `local − epoch = 1 163 565 µs`, matches the §A0.10 boot-delta measurement within 285 µs of WiFi MAC TX jitter. (b) **v0.7.0-esp32** — `csi_collector.c:221` ADR-018 byte 19 bit 4 ("cross-node sync valid") now ORs in `c6_sync_espnow_is_valid()` so frames from sync'd ESP-NOW nodes correctly advertise sync (previously only sourced from the broken 802.15.4 path — false-negative bug, §A0.13). Side effect: S3 boards now also set the bit since `c6_sync_espnow` is cross-target. **Host decoders + 25 unit tests**: Python `SyncPacketParser` + `SyncPacket` dataclass with `apply_to_local` / `mesh_aligned_us_for_sequence` / `local_minus_epoch_us` (10 tests in `TestSyncPacketParser`); Rust `wifi_densepose_hardware::SyncPacket` + `SyncPacketFlags` + `SYNC_PACKET_MAGIC` re-exported from the crate root with identical API surface (15 tests in `sync_packet::tests`). **Cross-language conformance gate** (loop iter 21): the same 32-byte canonical hex `10a111c509010600f26db70100000000c5aca501000000001400000000000000` is pinned in both test suites; if either decoder drifts from the wire, exactly one named test fires and points at the moved side. **Sensing-server wiring**: `udp_receiver_task` magic-dispatches `0xC511A110` and stores per-node `latest_sync: Option<SyncPacket>` + `latest_sync_at: Option<Instant>` on `NodeState`. New helpers: `NodeState::mesh_aligned_us(local_us)`, `NodeState::mesh_aligned_us_for_csi_frame(sequence)` (uses the per-node measured fps EMA with 5-sample warmup + 9 s staleness gate), `NodeState::observe_csi_frame_arrival(now)` (feeds `update_csi_fps_ema` α=1/8, called once per accepted CSI frame). 4 fps-EMA tests + 3 NodeSyncSnapshot serialization tests on the binary target. **Public JSON API**: `sensing_update` broadcasts now carry an optional `sync` object per node — `{offset_us, is_leader, is_valid, smoothed, sequence, csi_fps_ema, csi_fps_samples}` — `#[serde(skip_serializing_if = "Option::is_none")]` so non-mesh paths (multi-BSSID scan / synthetic-RSSI fallback / simulation) omit the key entirely. Existing pre-v0.7.0 UI clients ignore it cleanly. Documented in `docs/user-guide.md` "Per-node mesh sync (ADR-110)" section with field table, UI rendering rules, and the timestamp-recovery recipe. **Branch-coordination**: `docs/ADR-110-BRANCH-STATE.md` maps which files each of `adr-110-esp32c6` vs `feat/adr-115-ha-mqtt-matter` touches (regions are disjoint, merges should be clean line-merges). **Verification baselines**: full v2 cargo workspace at **1437 tests passing** (no regression across 17 crate batches), full `wifi-densepose-hardware` crate at **137 tests**. ADR-110 §B substrate is now end-to-end visible to UI clients and ready for ADR-029/030 multistatic CSI fusion consumption.
 - **Real-time CSI introspection / low-latency tap on `wifi-densepose-sensing-server` (ADR-099).**
   New `wifi_densepose_sensing_server::introspection` module wires
   [midstream](https://github.com/ruvnet/midstream)'s `temporal-attractor` (Lyapunov +