name: 'Set up build disk on hosted runners'
description: |
  Relocate Docker's data-root to /mnt (which has ~75 GB free, vs ~20 GB
  on / after free-disk-space). Combined with the apt cleanup, gives
  ~100 GB working space for buildx — enough for ROCm dev image + vLLM
  torch install + flash-attn build.

  No-op on:
    - self-hosted runners (no /mnt expectation)
    - non-X64 runners (verify /mnt shape on ubuntu-24.04-arm separately
      before enabling there — see Task 3.2 in the migration plan)
    - mode=skip (force-disable from caller)

  Must run after free-disk-space (which removes large packages — would
  fail mid-uninstall if Docker were stopped) and before any Docker
  operation (setup-qemu, setup-buildx, login, build) so the relocated
  data-root catches all subsequent docker activity.

inputs:
  mode:
    description: 'auto (default — relocate on hosted X64 only) or skip'
    required: false
    default: 'auto'

runs:
  using: 'composite'
  steps:
    - name: Relocate Docker data-root to /mnt
      if: inputs.mode == 'auto' && runner.environment == 'github-hosted' && runner.arch == 'X64'
      shell: bash
      run: |
        set -euo pipefail
        echo "Before relocation:"
        df -h / /mnt || true
        sudo systemctl stop docker docker.socket
        sudo mkdir -p /mnt/docker-data /mnt/docker-tmp
        # buildx CLI runs as the unprivileged runner user and creates
        # config dirs under TMPDIR before binding them into the buildkit
        # container. /mnt is owned by root by default; mirror /tmp's
        # 1777 (world-writable + sticky) so non-root processes can write.
        sudo chmod 1777 /mnt/docker-tmp
        if [ -d /var/lib/docker ] && [ ! -L /var/lib/docker ]; then
          sudo rsync -a /var/lib/docker/ /mnt/docker-data/
          sudo rm -rf /var/lib/docker
          sudo ln -s /mnt/docker-data /var/lib/docker
        fi
        # daemon.json may not exist; merge data-root in or create minimal.
        if [ -f /etc/docker/daemon.json ]; then
          sudo jq '."data-root" = "/mnt/docker-data"' /etc/docker/daemon.json | sudo tee /etc/docker/daemon.json.new >/dev/null
          sudo mv /etc/docker/daemon.json.new /etc/docker/daemon.json
        else
          echo '{"data-root":"/mnt/docker-data"}' | sudo tee /etc/docker/daemon.json
        fi
        sudo systemctl start docker
        # Make TMPDIR persist for subsequent steps in the same job.
        echo "TMPDIR=/mnt/docker-tmp" >> "$GITHUB_ENV"
        echo "After relocation:"
        df -h / /mnt
        docker info | grep -i 'docker root dir' || true