Web Serial / flashing isn't working

Flashing uses the browser's Web Serial API, which has requirements:

  1. Browser — use Chrome or Edge (Chromium). Firefox and Safari don't support Web Serial.
  2. Permission — you must pick the serial port in the browser prompt each session.
  3. USB — use a data-capable USB cable (not charge-only) and a direct port if possible.
  4. Drivers — some boards need a USB-UART driver (CP210x / CH340) installed at the OS level for the port to appear.
  5. Conflicts — close other serial monitors/IDEs holding the port.

Once the port appears and is selected, flashing proceeds.

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