Environment Skill

When to use this skill:

• You need to understand the environment architecture (for troubleshooting, modifications, or curiosity)
• You're modifying or extending the environment setup
• You encounter environment-related errors and need deeper context than error messages provide

When NOT to use this skill:

• Normal thesis work (build, test, commit) - error messages explain limitations
• You encounter a "local devcontainer only" error - the error message is sufficient

Environment Architecture

This project supports two environments:

1. Local Devcontainer (Jörn's machine)

• Defined by: .devcontainer/Dockerfile, .devcontainer/devcontainer.json, scripts/devcontainer-post-create.sh
• What it does: Pre-installs all dependencies (TexLive, Rust, Python, Node.js, etc.) in a Docker image
• Special features:
  • Bind mounts for cache persistence (/srv/devhome/* → /home/vscode/*)
  • Worktrees support (/workspaces/worktrees for git worktree isolation)
  • Shared Rust build cache via CARGO_TARGET_DIR=/workspaces/worktrees/shared/target

2. Claude Code Web Environment

• Defined by: Ubuntu 24.04 base with pre-installed language runtimes (see Claude Code docs)
• What it does: Provides a clean environment accessible from anywhere via web browser
• What's pre-installed: Rust, Python (with uv), Node.js, Git, build-essential
• What's NOT pre-installed: TexLive, latexml
• Key difference: No devcontainer files run, no bind mounts, no worktrees directory

Critical limitation (known bug as of Jan 2026):

• apt-get does NOT work in web environment (DNS blocked by proxy architecture)
• See: GitHub issue #14538
• Consequence: TexLive cannot be installed, LaTeX builds are local-only
• What works: cargo, uv/pip, npm (HTTP proxy compatible)
• What doesn't work: apt-get, dpkg, any system packages

Dependency Installation

Progressive Disclosure Strategy

Level 1: Error messages explain the situation

• Build/lint scripts check for dependencies and print clear errors
• Example: pdflatex not found (TexLive is local devcontainer only)

Level 2: This skill (understanding)

• Explains environment architecture
• Documents conventions for modifications

Level 3: Detailed implementation

• Devcontainer config files (.devcontainer/*)
• Reference docs in references/ subdirectory (if any)

What's Available Where

Conventions for Modifying Environments

When you need to add dependencies or modify environment setup:

1. Document with Progressive Disclosure

• CLAUDE.md: Add one-line note to Environment Dependencies section
• This skill: Explain architecture changes if significant
• Config files: Keep comments factual, avoid speculation

2. Install Script Conventions

If you create install scripts:

• Make scripts idempotent (check before installing)
• Print helpful messages about time/disk usage
• Support --help flag
• Point build/lint scripts to install script in error messages

3. Never Make False Claims

• Future agents will believe documentation literally
• Example: Don't call a 2GB install "slim"
• Example: Don't say "everywhere" when you mean "in local devcontainer"
• When uncertain, be explicit about what you don't know

4. Keep It Simple (KISS)

• Follow standard patterns (cargo, npm, pip/uv; apt-get in local only)
• Don't over-engineer for hypothetical future requirements
• Don't add noise to config files that agents don't need

5. Maintain Both Environments

• Local devcontainer: Bake dependencies into Dockerfile when reasonable
• Web environment: Only cargo/uv/npm work (no apt-get due to DNS bug)
• Test changes in both environments (or document what's untested)

6. DRY - Don't Repeat Yourself

• Information should live in ONE canonical place
• Link to that place rather than duplicating
• Exception: Error messages can repeat key info (like "local devcontainer only") for convenience

Common Tasks

Detecting Which Environment You're In

# Web environment has this variable
if [[ -n "${CLAUDE_CODE_REMOTE:-}" ]]; then
  echo "Running in web environment"
else
  echo "Running in local environment (or other)"
fi

Adding a New Dependency

For Python packages (works in both environments):

1. Add to packages/python_viterbo/pyproject.toml
2. Run uv sync --extra dev

For system dependencies (local devcontainer only):

1. Add to .devcontainer/Dockerfile
2. Update build scripts to fail gracefully with clear error in web environment
3. Update CLAUDE.md: Add one line to Environment Dependencies section

Fixing Environment-Specific Issues

Example: Rust builds depend on CARGO_TARGET_DIR=/workspaces/worktrees/shared/target in local, but that dir doesn't exist in web.

Approach:

1. Identify the constraint (worktrees mount only exists in local)
2. Make it environment-aware (unset CARGO_TARGET_DIR in web, or create dir)
3. Document the difference in this skill if non-obvious
4. Test both environments

Files to Read

• .devcontainer/Dockerfile - What's baked into local devcontainer image
• .devcontainer/devcontainer.json - Local devcontainer configuration
• scripts/devcontainer-post-create.sh - Local environment initialization
• .claude/CLAUDE.md - Top-level environment guidance for agents