The Pico W emulation runs in THIS browser tab via requestAnimationFrame.
Opening the gateway with target=_blank / window.open backgrounds the
emulation tab; the browser then pauses its rAF, the simulated chip
freezes, and the gateway can no longer reach the server on it — the
request times out (502) and toggles do nothing.
Render the served page in a same-tab iframe panel (openDeviceGateway) for
the Pico W so the emulation stays in the foreground and keeps answering.
The ESP32 is unchanged (its server runs in QEMU on the backend, immune to
tab visibility), so it keeps opening in a new tab.
Also: the async-led page now shows the LED state (the board's onboard LED
isn't drawn on the canvas) so the toggle has visible feedback.
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