AMD silently misbehaving on Salesforce Marketing Cloud

a-repro.js

define('foo', function () {
    function Foo () {
        Write('Hello World');
    };

    return Foo;
})

require(['foo'], function (Foo) {
    // Foo is undefined on Salesforce
    var f = new Foo();
})

b-workaround.js

// The workaround is to /not/ use RequireJS, and instead implement
// just the parts of the runtime that we need.

var moduleMap = {};
function resolve (deps) {
    var resolvedDeps = [];
    var resolved;
    for (var i=0, ii=deps.length; i<ii; ++i){
        resolved = moduleMap[deps[i]];
        if (resolved === undefined)
            throw new Error('Etsy RequireJS shim: could not find module ' + deps[i]);
        resolvedDeps.push(resolved);
    }
    return resolvedDeps;
}
function define (name, deps, fn) {
    if (typeof name !== 'string')
        throw new Error('Etsy RequireJS shim: you must specify a module name');
    if (fn == null) {
        fn = deps;
        deps = [];
    }
    if (typeof fn !== 'function')
        throw new Error('Etsy RequireJS shim: fn should be a Function');
    if (moduleMap[name] !== undefined)
        throw new Error('Etsy RequireJS shim: duplicate definition of ' + name);
    moduleMap[name] = fn.apply(null, resolve(deps));
}
define.amd = true;
function require (config, deps, fn) {
    if (fn == null) {
        fn = deps;
        deps = config;
        config = null;
    }
    if (deps == null) {
        fn = deps;
        deps = [];
    }
    if (typeof fn !== 'function')
        throw new Error('Etsy RequireJS shim: fn should be a Function');
    fn.apply(null, resolve(deps));
}