I'm serving data to be displayed in a gauge using the gauge.js library . It requires a couple of font files which it puts into the 'fonts' folder. I have put this into the 'fs' folder. I don't see the fonts in the 'Device Files' view but they are present in the 'Projects' view. so presumably they didn't get built into the image and hence not uploaded to the ESP32 target.
They are definitely missing because the gauge.js file can't find them either!!
Is this a restriction of the builder (I've been using sub-directories in Mongoose OK for years) ?