Environment variables for production and previews
Give a variable one value in production and another in pull request previews.
Every environment variable, at the service or the project level, now has a scope: All, Production or Preview. A value scoped to an environment overrides the All value with the same key, so you can point previews at a staging database or a test API key without touching production.
Existing variables keep working as before: they are scoped to All.
PR previews also got sturdier. A preview that was interrupted halfway is picked up again, and closing a pull request tears down its whole stack cleanly.