Drop two PNG files here before zipping the agent package:
color.png— 192×192, full coloroutline.png— 32×32, transparent background, white silhouette
These are required by the Teams app manifest and Microsoft 365 will reject the package if they are missing or the wrong dimensions.
You can generate placeholders with ImageMagick:
convert -size 192x192 xc:'#2A6DF4' agent/appPackage/color.png
convert -size 32x32 xc:none -fill white -draw "circle 16,16 16,4" agent/appPackage/outline.png