The "Open in Dev Container" badge is one of the highest-friction-to-value improvements you can make to a developer tool. Someone lands on your README, clicks the badge, waits for a container to build, and starts using the tool — no install steps, no certificate trust ceremony, no "is port 8899 available on this machine" questions. The conversion from "interesting project" to "I am actually running this" happens in the time it takes Docker to pull an image. Getting there, however, requires navigating a specific class of problems that are not particularly hard once you understand them but are completely opaque until you do. This post is a technical account of building the Topaz devcontainer: the three services that ended up in the Docker Compose file, why /etc/resolv.conf defeated two consecutive DNS approaches, and what the working architecture looks like.…