Use Docker Compose as the base of a dev container: dockerComposeFile, service, runServices, workspaceFolder, overrideCommand

Documented steps

1. Create docker-compose.yml with your dev service (e.g. app) plus supporting services (e.g. db); give the dev service command: sleep infinity so it stays alive as a dev box
2. Bind-mount the source into the dev service: volumes: [ ..:/workspaces/myproject:cached ] (paths resolve relative to the compose file's directory)
3. Point devcontainer.json at it: {"dockerComposeFile": "docker-compose.yml", "service": "app", "workspaceFolder": "/workspaces/myproject"}
4. Limit which services auto-start with runServices: ["app", "db"] (default is all services in the file)
5. Reach sibling services by their compose service name (db:5432) on the shared compose network, or use forwardPorts: ["db:5432"] to expose them to the host
6. Note overrideCommand defaults differ: true for image/Dockerfile containers (tool replaces the command with a sleep loop) but FALSE for Docker Compose — so your compose command runs as-is; that's why the sleep-infinity command in the compose file matters
7. Docs: https://code.visualstudio.com/docs/devcontainers/create-dev-container | https://containers.dev/implementors/json_reference/