The executable’s icon

The player's executable carries the Tassix icon: apps/player/tassix.ico (16 to 256 pixels; written by tassix_player --export-icon with no game) becomes a compiled resource file in the player's build script, which the MSVC linker takes as an input (no resource compiler needed).
tassix_player --export-icon <out.ico> writes the icon a game's window shows (the Unity project's, game.json's, or Tassix's), fitted to each size: 32-bit bitmaps up to 128 pixels and a PNG at 256. cargo xtask package exports it from the packaged game and writes it into the executable's resources (icon group 1 and its images, through the Windows resource update API), so Explorer shows the game's icon.
Checked: a unit test of the .ico (its sizes, bitmaps and PNG); the built player's and a packaged sample's icons, extracted from the executables by Windows; the packaged executable still runs.
Next: UI Toolkit numeric fields (IntegerField, FloatField); virtualized ListView.