Verified empirically: fontkit has no default ESM export in this project's
"type": "module" setup (import fontkit from 'fontkit' throws). The working
form is import * as fontkit from 'fontkit'.
Empirically verified library choices (fonteditor-core, opentype.js, fontkit)
against real fonts before committing to the scope, and root-caused a
file-type/dfont MIME collision that would otherwise silently break uploads.
anthony