Adds a dedicated blocking serial-reader thread that opens the
HLK-LD2402 over a CP2102 USB-UART bridge (default 115200 8N1),
parses ASCII `distance:<cm>\r\n` lines @ ~6 Hz, stores the latest
reading in a static OnceLock<Mutex<…>>, and exposes it via:
GET /api/v1/mmwave/latest →
{ "available": true, "distance_cm": 152, "age_ms": 90 }
{ "available": false } (port absent, stale > 2 s)
UI (Sensing tab) polls the endpoint every visible WS tick and
shows a new blue card "mmWave Radar (24 GHz)" with distance +
age bar. Card hides when unavailable.
CLI:
--mmwave-port /dev/cu.usbserial-1140
--mmwave-baud 115200 (default)
Both optional — server runs as before if the module is absent.
Open failure: single WARN log, reader thread exits, server keeps
serving WiFi sensing.
Verified live: distance 149-153 cm at ~6 Hz, REST returns fresh
readings with age_ms 55-127.
Out of scope (logged in ADR-121): Engineering Mode binary frames,
vitals cross-check vs ADR-021, W-MLP feature fusion, auto-reconnect.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
cb6e24ed57