Node.js
On every start the server runs npm install (using your package.json) before starting the bot. Make sure package.json lists everything: npm install discord.js --save on your PC adds it. Do not upload node_modules/. It is huge, platform-specific, and gets rebuilt anyway.
Need a package that is not in package.json? Startup → NODE_MODULES → space-separated names (discord.js dotenv) installs them additionally.
Lock files (package-lock.json) are respected; upload them for reproducible installs.
Python
On every start: pip install -r requirements.txt (the file name is in Startup → REQUIREMENTS_FILE), plus any packages listed in PY_PACKAGES. Create the file on your PC with pip freeze > requirements.txt in your virtual environment, then remove packages you do not actually use.
Speed
Installs run each start, but npm and pip cache; after the first start it takes seconds. If your bot restarts every few minutes because of a crash, fix the crash. Reinstalling in a loop is what you see in the console.
Native modules
Packages that compile C code (canvas, sharp, some audio libraries) need build tools. Most ship prebuilt binaries for Linux x64 and just work; if one fails to build, ask Kowalski to read the install log. The fix is usually a different package version.