Design a CI/CD pipeline for a monorepo with 200 microservices. How do you handle selective builds, dependency ordering, and deployment orchestration?

# GitHub Actions: Selective build with path filters
name: CI
on:
  push:
    branches: [main]
  pull_request:

jobs:
  detect-changes:
    runs-on: ubuntu-latest
    outputs:
      services: ${{ steps.changes.outputs.services }}
    steps:
      - uses: actions/checkout@v4
        with: { fetch-depth: 0 }
      - id: changes
        run: |
          changed=$(git diff --name-only ${{ github.event.before }} HEAD | \
            grep -oP 'services/\K[^/]+' | sort -u | jq -R -s -c 'split("\n") | map(select(. != ""))')
          echo "services=$changed" >> $GITHUB_OUTPUT

  build:
    needs: detect-changes
    strategy:
      matrix:
        service: ${{ fromJson(needs.detect-changes.outputs.services) }}
    steps:
      - run: echo "Building ${{ matrix.service }}"