How do you structure a mono-repo CI/CD pipeline to avoid unnecessary builds?

In a monorepo with 20+ services, you must only trigger builds for services that actually changed. Strategies:

• Path filters: GitHub Actions paths: filter to trigger workflows only when specific directories change.
• Nx / Turborepo: Task runners with build graph awareness that skip unchanged services.
• git diff: Compare changed files against the base branch and only build affected services.

# GitHub Actions path filter
on:
  push:
    paths:
      - "services/api/**"
      - "shared/lib/**"