feat: 4 sensing examples — sleep apnea, stress, room environment

examples/sleep/apnea_screener.py — detects breathing cessation
events (>10s), computes AHI score, classifies OSA severity.

examples/stress/hrv_stress_monitor.py — real-time SDNN/RMSSD
from mmWave HR, stress level with visual bar.

examples/environment/room_monitor.py — dual-sensor (CSI + mmWave)
room awareness: occupancy, light, RF fingerprint, activity events.

examples/README.md — index with hardware table and quick start.

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

examples/stress/hrv_stress_monitor.py

@@ -0,0 +1,149 @@
+#!/usr/bin/env python3
+"""
+Real-Time Stress Monitor via Heart Rate Variability (HRV)
+
+Reads heart rate from MR60BHA2 mmWave radar and computes HRV metrics
+to estimate stress level continuously.
+
+HRV Science:
+  - SDNN < 50ms = high stress / low parasympathetic tone
+  - SDNN 50-100ms = moderate
+  - SDNN > 100ms = relaxed / high vagal tone
+  - RMSSD: successive difference metric, more sensitive to acute stress
+
+Usage:
+    python examples/stress/hrv_stress_monitor.py --port COM4
+"""
+
+import argparse
+import collections
+import math
+import re
+import serial
+import sys
+import time
+
+RE_HR = re.compile(r"'Real-time heart rate'.*?(\d+\.?\d*)\s*bpm", re.IGNORECASE)
+RE_ANSI = re.compile(r"\x1b\[[0-9;]*m")
+
+
+def compute_hrv(hr_values):
+    """Compute HRV metrics from HR time series."""
+    if len(hr_values) < 5:
+        return {"sdnn": 0, "rmssd": 0, "mean_hr": 0, "stress": "—"}
+
+    rr = [60000.0 / h for h in hr_values if h > 0]
+    if len(rr) < 5:
+        return {"sdnn": 0, "rmssd": 0, "mean_hr": 0, "stress": "—"}
+
+    mean_rr = sum(rr) / len(rr)
+    sdnn = math.sqrt(sum((x - mean_rr) ** 2 for x in rr) / len(rr))
+
+    # RMSSD: root mean square of successive differences
+    diffs = [(rr[i+1] - rr[i]) ** 2 for i in range(len(rr) - 1)]
+    rmssd = math.sqrt(sum(diffs) / len(diffs)) if diffs else 0
+
+    mean_hr = sum(hr_values) / len(hr_values)
+
+    if sdnn < 30:
+        stress = "HIGH STRESS"
+    elif sdnn < 50:
+        stress = "Moderate Stress"
+    elif sdnn < 80:
+        stress = "Mild Stress"
+    elif sdnn < 100:
+        stress = "Relaxed"
+    else:
+        stress = "Very Relaxed"
+
+    return {"sdnn": sdnn, "rmssd": rmssd, "mean_hr": mean_hr, "stress": stress}
+
+
+def stress_bar(sdnn, width=30):
+    """Visual stress bar: more filled = more stressed."""
+    level = max(0, min(1, 1.0 - sdnn / 120.0))
+    filled = int(level * width)
+    bar = "#" * filled + "." * (width - filled)
+    return f"[{bar}] {level*100:.0f}%"
+
+
+def main():
+    parser = argparse.ArgumentParser(description="HRV Stress Monitor (mmWave)")
+    parser.add_argument("--port", default="COM4")
+    parser.add_argument("--baud", type=int, default=115200)
+    parser.add_argument("--duration", type=int, default=120)
+    parser.add_argument("--window", type=int, default=60, help="HRV window in seconds")
+    args = parser.parse_args()
+
+    ser = serial.Serial(args.port, args.baud, timeout=1)
+
+    print()
+    print("=" * 60)
+    print("  Real-Time Stress Monitor (mmWave HRV)")
+    print("  Sit still within 1m. Lower stress = higher HRV.")
+    print("=" * 60)
+    print()
+
+    hr_buffer = collections.deque(maxlen=args.window)
+    start = time.time()
+    last_print = 0
+    min_stress = 999.0
+    max_stress = 0.0
+    readings = []
+
+    try:
+        while time.time() - start < args.duration:
+            line = ser.readline().decode("utf-8", errors="replace")
+            clean = RE_ANSI.sub("", line)
+
+            m = RE_HR.search(clean)
+            if m:
+                hr = float(m.group(1))
+                if 30 < hr < 200:
+                    hr_buffer.append(hr)
+
+            elapsed = int(time.time() - start)
+            if elapsed > last_print and elapsed % 5 == 0 and len(hr_buffer) >= 3:
+                last_print = elapsed
+                hrv = compute_hrv(list(hr_buffer))
+                bar = stress_bar(hrv["sdnn"])
+                readings.append(hrv)
+
+                if hrv["sdnn"] > 0:
+                    min_stress = min(min_stress, hrv["sdnn"])
+                    max_stress = max(max_stress, hrv["sdnn"])
+
+                print(f"  {elapsed:>4}s | HR {hrv['mean_hr']:>4.0f} | "
+                      f"SDNN {hrv['sdnn']:>5.1f}ms | RMSSD {hrv['rmssd']:>5.1f}ms | "
+                      f"{hrv['stress']:<16} | {bar}")
+
+    except KeyboardInterrupt:
+        pass
+
+    ser.close()
+
+    print()
+    print("=" * 60)
+    print("  STRESS SESSION SUMMARY")
+    print("=" * 60)
+    if readings:
+        avg_sdnn = sum(r["sdnn"] for r in readings) / len(readings)
+        avg_rmssd = sum(r["rmssd"] for r in readings) / len(readings)
+        avg_hr = sum(r["mean_hr"] for r in readings) / len(readings)
+        final_stress = readings[-1]["stress"]
+
+        print(f"  Duration:    {time.time()-start:.0f}s")
+        print(f"  Avg HR:      {avg_hr:.0f} bpm")
+        print(f"  Avg SDNN:    {avg_sdnn:.1f} ms {'(low — consider a break)' if avg_sdnn < 50 else '(healthy range)' if avg_sdnn > 70 else ''}")
+        print(f"  Avg RMSSD:   {avg_rmssd:.1f} ms")
+        print(f"  SDNN range:  {min_stress:.0f} - {max_stress:.0f} ms")
+        print(f"  Assessment:  {final_stress}")
+        print()
+        print("  SDNN Guide: <30=high stress, 30-50=moderate, 50-100=normal, >100=relaxed")
+    else:
+        print("  No data collected. Ensure person is in range.")
+    print()
+
+
+if __name__ == "__main__":
+    main()