How to reuse an environment between jobs?

I have a simple workflow for my home app (front and back), all in one job, running on self-hosted runners:

• prepare environments for the builds (apt install ...)
• build the front to a directory spa
• copy the directory spa to the sources of the back
• build the back (this will embed the spa directory in the binary)
• deploy the binary to the home server

The reason for which these steps are linear is that I need the output from the front build for the back build.

This setup works.

name: build-n-deploy
on: push
jobs:
  dash:
    runs-on: self-hosted
    steps:
      - uses: actions/checkout@v2
        with:
          ref: master
      - name: prepare build environment
        run: |
          apt update
          apt install software-properties-common -y
          add-apt-repository ppa:longsleep/golang-backports -y
          curl -fsSL https://deb.nodesource.com/setup_14.x | sudo -E bash -
          apt update && apt dist-upgrade -y
          apt install nodejs -y
          apt install golang-go -y
          npm install -g @quasar/cli
      - name: build front
        working-directory: ./front
        run: |
          npm install
          quasar build
          cp -r dist/spa ../back
      - name: compile back
        working-directory: ./back
        run: |
          env GOOS=linux GOARCH=arm GOARM=5 go build -o dash.rpi
      - name: deploy server files
      (...)

For the sake of better understanding GitHub Actions and a more organized setup, I wanted to split this into several distinct jobs (rectangles with description below):

The environment preparation (that takes the most time) would run in parallel on two self-hosted runners.

I have one problem with this setup: I would obviously like to reuse the build environments for the actual build (the bolded red arrow in the flowchart above). How can I instruct a job to run in the environment of a previous job?

the other point is to transfer the directory spa generated during the build of the front to be the build of the back - for that I will use artifacts.