feat(adr-125 tier1+2 iter 2): sensing-server-equivalent for @ruvnet/rvagent

scripts/ruview-sensing-server.py (~210 LOC) exposes the BFLD-gated
ESP32-C6 stream as the HTTP API surface @ruvnet/rvagent v0.1.0
(ADR-124, npm) expects. Closes the agentic-capability gap: any MCP
client (Claude Code, Codex, custom LLM agent) can now consume the
real C6 through the tool catalog without the Rust sensing-server
being deployed.

Endpoints (mirrors tools/ruview-mcp/src/tools/*.ts):

  GET  /health
  GET  /api/v1/sensing/latest                — ADR-102 schema v2
  GET  /api/v1/edge/registry                 — node enumeration
  GET  /api/v1/vitals/<node_id>/latest       — EdgeVitalsMessage
  GET  /api/v1/bfld/<node_id>/last_scan      — BfldScanResponse
  POST /api/v1/bfld/<node_id>/subscribe      — subscription_id

c6-presence-watcher.py now writes a companion `/tmp/ruview-last-
feature.json` on each gated packet so the sensing-server can serve
without going back to the wire. Atomic tmp+rename. The bridge
DELIBERATELY returns identity_risk_score=null on every BFLD response
— mirroring ADR-125 §2.1.d at the HTTP boundary even though the
rvagent schema's slot is nullable.

Live smoke test against the real C6 (node_id=12):

  $ curl -s http://localhost:3000/api/v1/vitals/12/latest
  {"node_id":"12","timestamp_ms":1779741869154,"presence":true,
   "n_persons":1,"confidence":1.0,"breathing_rate_bpm":18.75,
   "heartrate_bpm":40.0,"motion":1.0}

  $ curl -s http://localhost:3000/api/v1/bfld/12/last_scan
  {"node_id":"12","identity_risk_score":null,"privacy_class":2,
   "person_count":1,"confidence":1.0,"presence":true,
   "timestamp_ns":1779741869154607104}

  $ curl -s -X POST 'http://localhost:3000/api/v1/bfld/12/subscribe?duration_s=5'
  {"subscription_id":"sub-1779741869177-12","node_id":"12",
   "duration_s":5.0,"endpoint_hint":"poll GET ..."}

Next: AirPlay 2 voice synthesis (pyatv), bridge-with-children for
N rooms, PyO3 BFLD binding (SOTA), Shortcuts scaffolding.

Refs ADR-124 (@ruvnet/rvagent contract), ADR-125 §2.1.d, ADR-118.

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

scripts/c6-presence-watcher.py

@@ -268,6 +268,37 @@ def main() -> int:
         except OSError:
             pass
 
+    # Companion contract for `scripts/ruview-sensing-server.py` (the
+    # @ruvnet/rvagent compatibility layer): write the full BFLD-gated
+    # feature snapshot so the sensing-server can serve EdgeVitalsMessage
+    # and BfldScanResponse without going back to the wire.
+    feature_path = "/tmp/ruview-last-feature.json"
+
+    def write_feature(gated: dict, motion: bool, occupancy: bool,
+                      privacy_cls: int) -> None:
+        try:
+            tmp = feature_path + ".tmp"
+            with open(tmp, "w") as fh:
+                json.dump({
+                    "node_id": str(gated["node_id"]),
+                    "timestamp_ms": int(time.time() * 1000),
+                    "presence": occupancy,           # sustained
+                    "motion": gated["motion"],        # 0..1 float
+                    "presence_score": gated["presence"],
+                    "n_persons": 1 if occupancy else 0,
+                    "confidence": min(1.0, max(0.0, gated["motion"])),
+                    "breathing_rate_bpm": (gated["resp_bpm"]
+                                           if gated.get("resp_bpm") else None),
+                    "heartrate_bpm": (gated["hb_bpm"]
+                                      if gated.get("hb_bpm") else None),
+                    "anomaly_score": gated.get("anomaly"),
+                    "privacy_class": privacy_cls,
+                    "ts": time.time(),
+                }, fh)
+            os.replace(tmp, feature_path)
+        except OSError:
+            pass
+
     while running:
         try:
             buf, _addr = sock.recvfrom(2048)
@@ -336,6 +367,8 @@ def main() -> int:
                         if (motion != prev_motion
                                 or not state_path.endswith(".disabled")):
                             write_state(motion, occupancy, last_anomaly_ts)
+                            write_feature(gated, motion, occupancy,
+                                          privacy_class)
 
         # Idle release — if the C6 stops sending entirely, clear motion
         # AND occupancy.