Shelly Duo GU10 Gotchas

When working with Shelly Duo GU10 RGBW smart bulbs (Gen1 / shellycolorbulb- family) over LAN HTTP:

• LAN-only API. No cloud round-trip required — this is the killer feature vs Govee. Latency ~30–80 ms on a healthy WiFi network. Use min-interval 0.2 s for any debounce controller, not the 1.2 s you'd use for cloud APIs.
• mDNS discovery name: _http._tcp.local. with service name pattern shellycolorbulb-<MAC> (last 6 hex digits of the MAC, lowercase). For Duo GU10 specifically the prefix may also be shellybulbduo-<MAC>.
• mDNS bind gotcha: JmDNS.create() with no argument binds to the JVM's default InetAddress, which on macOS is localhost (127.0.0.1) by default. Discovery returns nothing. You must bind to the primary non-loopback IPv4 interface explicitly.
• Color endpoint: GET /color/0?turn=on&red=R&green=G&blue=B&gain=N where R/G/B are 0..255 and gain is 0..100.
• Off: GET /color/0?turn=off. The bulb retains last R/G/B for the next turn=on.
• White / temperature mode: GET /white/0?turn=on&temp=K&brightness=N where temp is 3000..6500. Mode is sticky — if you set white mode, the next /color/0?turn=on may not pick the previous color cleanly. Reset color explicitly.
• Status / health: GET /status returns JSON with lights[0].ison, wifi_sta.ip, rssi, etc. Use for liveness probe.
• No HTTPS. No auth by default (factory defaults). If you've set a Shelly password, requests need HTTP Basic auth.
• Power-cycling resets the IP unless you've reserved it in the router. For demos, use a router DHCP reservation OR set a static IP via the Shelly web UI.

See the full skill at skills/shelly-duo-gu10-control/SKILL.md for the Kotlin/Ktor reference client and JmDNS discovery example.