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Agent VMs use a two-layer image:
  1. Platform base — Debian 12, Git, Node.js, Claude Code, Codex CLI, gh CLI. Maintained by Murmur.
  2. Your toolchain — Go, Python, Docker, Chrome, internal SDKs. Built by baking a recipe on top of the base.
Your workspace references an image by name via the image_ref field.

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How images are created

Images are produced by the bake process. You define a recipe (base image + provisioning script), then run murmur bake — it executes immediately under your own authority, or stages an executable change-request action for review with --propose. The platform creates a scratch VM, runs your script, snapshots the result, and registers the image. Images are bound to placements — a GCE image baked in one project is not visible from another. When you create a customer placement, you re-bake your recipes so the images exist in your cloud account.

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Immutability

Baked images are immutable — you cannot edit one after it is created. To change what’s installed, update your recipe and re-bake. List existing images with murmur get image.

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Automatic image updates

Images are rebuilt for you when an agent reports a defect in one — a missing tool, a command not found, a package too old. Because the fix is a change to the recipe the image is baked from, that service is described with recipes: see automatic recipe updates for what it does, and how to have it propose changes for review instead of applying them.