The "Approx. download: $ kb" display on the lower status bar of the C2 UI does not seem to include the size of the c2runtime. This is potentially problematic, because publishers tend to having hard size limits for download packages for mobile and people might realize their mistake too late in the process.
To include c2runtime in the size calculation, or (preferred): have two seperate numbers, one "total download size" and one "assets only"
Construct 2 version:
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Closing as by design, it's deliberately not included. It's very hard to accurately estimate the final download size at export, because the export process involves sophisticated script minification processes (using Google Closure Compiler), and much more significantly, sophisticated image spritesheeting and recompression. This can change the size of the project by megabytes, so the estimated size is deliberately very rough. If it could be accurate to within 1mb that would be an excellent result, and usually the total script size is under 1mb, so for the purposes of the estimation the script size is basically negligable.