Define a project with stackblaze.yaml
The file is stackblaze.yaml. The template catalog is a different path: + Service → Templates. IaC apply is off until you enable it on the project.
You can also import render.yaml, fly.toml, docker-compose, or stackblaze.yaml from + Service → Import. That stages nodes on the canvas. It does not apply them until you commit (or run apply, if IaC is on).
Step by step
Export a live phase (optional)
On the canvas, use Save as stack to export the current project/phase as stackblaze.yaml. Credentials are not written into the file.
Enable IaC apply when you want plan/apply
Project Settings → General → Infrastructure as Code → Enable IaC apply. This is per project, not a tenant-wide switch.
Plan, then apply
Plan shows what would be created or updated. Apply upserts. Apply never deletes apps or add-ons that are missing from the file.
Templates vs IaC
A catalog template deploys a known stack. A stackblaze.yaml you own is the declarative form of your phase. Do not treat “Blueprint” as a third product.