Heroku not running the postinstall or heroku-postbuild commands:

I'm trying to deploy an app that makes use of the MRE SDK to Heroku. As of this writing, the SDK itself is broken, and attempting to run an npm run build will result in an error.

A work around is to copy a modified animation.d.ts file over to the resulting node_modules folder, after the install (specifically ./node_modules/@microsoft/mixed-reality-extension-sdk/built/animation/).

I keep this file in a folder called v0.16_mre_fix.

Without this, the build will fail. So I added this to my package.json file.

"scripts": {
        "test": "echo \"Error: no test specified\" && exit 1",
        "clean": "tsc --build --clean",
        "heroku-postbuild": "cp -i ./v0.16_mre_fix/*.ts ./node_modules/@microsoft/mixed-reality-extension-sdk/built/animation/",
        "build": "tslint -p ./tsconfig.json src/**/*.ts && tsc --build",
        "lint": "tslint -p ./tsconfig.json src/**/*.ts",
        "start": "node .",
        "debug": "node --nolazy --inspect-brk=9229 ."
    },

According to heroku here, heroku-postbuild will be run after installing dependencies. This, however, did not work.

So I tried changing it to heroku-prebuild and postinstall:. They didn't work either.

Am I missing something?

EDIT: I also tried

"heroku-prebuild": "echo This runs before Heroku installs your dependencies.",

but I didn't see any echo in the ensuing git push.