Devcontainer Bridge

Container-Bridge Skill

This skill bridges the agent into a running dev-container so all CLI commands execute in the project's defined environment — not the host machine. The container is defined by .devcontainer/devcontainer.json and may install tools via postCreateCommand or features — check that file first to understand what's available inside.

When to use this skill

• The workspace has a .devcontainer/devcontainer.json file
• The task involves running any CLI command, build step, or test suite
• The user asks to "run in the container" or "use the dev environment"
• The command requires tools that aren't guaranteed to exist on the host (e.g., specific Node versions, Python envs, project-specific CLIs)

Do not bridge for browser automation or tasks explicitly intended for the host.

Step 1: Detect the environment

Check that the right pieces are in place before attempting a bridge:

# Confirm devcontainer config exists
ls .devcontainer/devcontainer.json

# Confirm Docker daemon is running
docker info --format '{{.ServerVersion}}'

# Confirm devcontainer CLI is available
devcontainer --version

If devcontainer CLI is missing, install it:

npm install -g @devcontainers/cli

If Docker isn't running, inform the user — the container won't start without it.

Step 2: Start the container (if not already running)

devcontainer up --workspace-folder .

This is idempotent — safe to run even if the container is already up. It will pull the image on first run, which can take a minute.

Step 3: Establish a persistent bridge session

Use run_command with RunPersistent: true to create a reusable terminal session inside the container:

run_command:
  CommandLine: devcontainer exec --workspace-folder . bash
  RunPersistent: true

Save the returned TerminalID. All subsequent commands should reuse this ID so they run in the same container shell — this preserves environment variables, working directory, and avoids container startup overhead on every command.

Step 4: Verify the bridge

First, read the expected remote user from the devcontainer config on the host:

cat .devcontainer/devcontainer.json | grep remoteUser

Then, inside the container session, run a generic OS identity check:

uname -a && id && pwd

Confirm:

• uname shows Linux (not Darwin) — you're inside the container, not the host
• id shows the user matches the remoteUser value from devcontainer.json
• pwd reflects the workspace directory

If postCreateCommand tools aren't available yet, wait a moment or check the Docker logs for the setup progress (docker logs <container-id>).

Step 5: Execute commands via the persistent session

All build, test, and CLI commands should be sent as input to the stored TerminalID:

send_command_input:
  CommandId: <TerminalID from Step 3>
  Input: <your command here>\n

Error recovery: If a command fails unexpectedly, check whether the container is still running (docker ps). If the session was lost, repeat from Step 3 to re-establish the bridge. You do not need to re-run devcontainer up.

Step 6: Clean up (optional)

There's no need to explicitly stop the container after each task — Docker containers persist until the user stops them or restarts Docker. Close the persistent terminal session when the task is complete to free resources.

Reminders

• Check devcontainer.json for bind mounts — host paths mounted into the container affect credential and config access
• The remote user varies by project — always check remoteUser in devcontainer.json to know who owns files created inside the container
• Host-side tasks (browser automation, file access outside workspace) should use host tools directly, not the container bridge