Fable bootstrapping itself to compile F# code in JS-only environments (browser, node.js). Note this doesn't output JS code, but a JSON AST that must be transformed using Babel.

package.json carries the version of Fable this bundle was built from:

{
    "version": "3.0.0",
    "fableVersion": "5.14.0"
}

A precompiled library can only be read by the Fable that wrote it, so a host that passes precompiledInfo to CreateChecker has to run fable precompile with that exact version. The npm version does not say which one it is, and manager.Version only answers once the checker is already loaded - too late to choose a compiler. Read this field instead, and pin dotnet fable to it.