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name: cross-platform-guardian description: Ensure cross-platform compatibility across macOS (Intel/ARM), Ubuntu, and Fedora for this dotfiles repository. Detects and auto-fixes hardcoded paths, platform-specific assumptions, package availability issues, and test coverage gaps. Use when adding features, updating configs, bumping Nix flake, or investigating platform-specific bugs. Keywords: cross-platform, compatibility, macOS, Linux, Ubuntu, Fedora, platform, portability, Nix flake, Docker test, CI allowed-tools: Read, Write, Edit, Grep, Glob, Bash

Cross-Platform Guardian

Maintains cross-platform compatibility across macOS (Intel/ARM), Ubuntu, and Fedora by detecting issues, auto-fixing violations, and ensuring reproducibility through Nix + Docker testing.

Activation Triggers

Use this skill when:

• Adding new scripts, configs, or features
• Updating flake.nix or flake.lock
• Investigating platform-specific failures in CI
• Refactoring installation/setup logic
• User mentions: "compatibility", "cross-platform", "works on Mac but not Linux", "CI failing on Fedora"

Core Responsibilities

1. Compatibility Audit

Scan for anti-patterns:

Hardcoded paths:

# ❌ BAD
DOTFILES_DIR="/Users/wcygan/Development/dotfiles"
CONFIG_PATH="/home/user/.config"

# ✅ GOOD
DOTFILES_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
CONFIG_PATH="${XDG_CONFIG_HOME:-$HOME/.config}"

Platform-specific commands without fallback:

# ❌ BAD
open README.md  # macOS only

# ✅ GOOD
if [[ "$OSTYPE" == "darwin"* ]]; then
  open README.md
else
  xdg-open README.md
fi

Architecture assumptions:

# ❌ BAD
HOMEBREW_PATH="/opt/homebrew"  # ARM only

# ✅ GOOD
if [[ -d "/opt/homebrew" ]]; then
  HOMEBREW_PATH="/opt/homebrew"  # Apple Silicon
elif [[ -d "/usr/local/Homebrew" ]]; then
  HOMEBREW_PATH="/usr/local"     # Intel Mac
fi

Shell assumptions:

# ❌ BAD - assumes bash arrays work everywhere
declare -a packages=(git fish)

# ✅ GOOD - POSIX-compatible or gated
if [[ -n "$BASH_VERSION" ]]; then
  declare -a packages=(git fish)
fi

2. Platform Detection Validation

Verify multi-layer detection exists:

In bash scripts (install.sh, scripts/*.sh):

if [[ "$OSTYPE" == "darwin"* ]]; then
  echo "macOS detected"
elif [[ -f /etc/fedora-release ]]; then
  echo "Fedora detected"
elif [[ -f /etc/lsb-release ]] && grep -q Ubuntu /etc/lsb-release; then
  echo "Ubuntu detected"
elif [[ -f /etc/os-release ]]; then
  echo "Generic Linux detected"
else
  echo "⚠️  Unsupported OS - proceeding with defaults"
fi

In Fish configs (config/fish/conf.d/*.fish):

switch (uname)
  case Darwin
    # macOS logic
  case Linux
    # Linux logic
end

Container detection:

if [[ -f /.dockerenv ]] || [[ -n "$container" ]] || ! command -v systemctl &>/dev/null; then
  IS_CONTAINER=true
fi

3. Nix Flake Compatibility

Check flake.nix supports all target architectures:

allSystems = [
  "x86_64-linux"   # Intel/AMD Linux
  "aarch64-linux"  # ARM Linux
  "x86_64-darwin"  # Intel Mac
  "aarch64-darwin" # Apple Silicon
];

Validate package availability:

• After updating flake.lock, check if any packages fail on specific platforms
• Use nix flake show to verify outputs for all systems
• Run scripts/test-platform-compatibility.sh (create if missing)

Auto-fix strategy for unavailable packages:

# Add platform-specific conditionals if needed
packages = with pkgs; [
  git fish starship  # Universal
] ++ lib.optionals stdenv.isDarwin [
  # macOS-specific packages
] ++ lib.optionals stdenv.isLinux [
  # Linux-specific packages
];

4. Path Standardization

XDG Base Directory compliance:

Config Type	macOS	Linux	Standard
Fish	~/.config/fish	~/.config/fish	✅ XDG
Starship	~/.config/starship.toml	~/.config/starship.toml	✅ XDG
VSCode	~/Library/Application Support/Code/User	~/.config/Code/User	❌ Platform-specific
tmux	~/.tmux.conf	~/.tmux.conf	❌ Legacy

Detection pattern in scripts/link-config.sh:

if [[ "$OSTYPE" == "darwin"* ]]; then
  VSCODE_DIR="$HOME/Library/Application Support/Code/User"
else
  VSCODE_DIR="${XDG_CONFIG_HOME:-$HOME/.config}/Code/User"
fi

5. CI/CD Test Coverage

Verify GitHub Actions matrix includes:

# .github/workflows/ci.yml
jobs:
  docker-matrix:
    strategy:
      matrix:
        include:
          - os: ubuntu-25.04
            dockerfile: tests/Dockerfile.ubuntu
          - os: fedora-40
            dockerfile: tests/Dockerfile.fedora

  native-test:
    strategy:
      matrix:
        os: [ubuntu-latest, macos-latest]

Test script validation (tests/docker-test-commands.fish):

• Must have conditional checks: if type -q <tool>
• Must not assume specific paths
• Must handle missing tools gracefully

6. Auto-Fix Workflow

When compatibility issues detected:

Step 1: Identify violations

# Use scripts/audit-compatibility.sh (create if missing)
grep -r "/Users/wcygan" scripts/ config/
grep -r "open " scripts/ | grep -v "xdg-open"

Step 2: Apply fixes automatically

# Fix hardcoded paths
sed -i.bak 's|/Users/wcygan/Development/dotfiles|$(cd "$(dirname "${BASH_SOURCE[0]}")/.." \&\& pwd)|g' scripts/*.sh

# Fix platform-specific commands
# Use Edit tool to replace `open` with conditional logic

Step 3: Validate fixes

make test-pre          # Local syntax checks
make test-docker       # Docker matrix (Ubuntu + Fedora)

Step 4: Update tests

• Add regression test for fixed issue in tests/docker-test-commands.fish
• Document fix in commit message with fix(compat): <description>

7. Nix Flake Update Protocol

When user requests flake update or this skill detects outdated lock:

Step 1: Update flake.lock

nix flake update

Step 2: Test across all platforms in CI

# Trigger CI workflow or run locally
make test-docker  # Tests Ubuntu + Fedora

Step 3: Check for package availability issues

# Attempt build for each system
nix build .#packages.x86_64-linux.default --dry-run
nix build .#packages.aarch64-linux.default --dry-run
nix build .#packages.x86_64-darwin.default --dry-run
nix build .#packages.aarch64-darwin.default --dry-run

Step 4: Handle failures

• If package unavailable on platform → add to platform-specific list or remove
• If build fails → rollback flake.lock and investigate
• Update flake.lock only if all platforms pass

8. Common Issue Patterns

Issue: Script uses bash-isms in shebang marked as sh

# ❌ BAD
#!/bin/sh
declare -a arr=(one two)  # bash-only

# ✅ GOOD
#!/usr/bin/env bash
declare -a arr=(one two)

Issue: Missing container detection in Nix install

# ✅ GOOD (from scripts/install-nix.sh)
if [[ -f /.dockerenv ]] || [[ -n "$container" ]]; then
  curl --proto '=https' --tlsv1.2 -sSf -L https://install.determinate.systems/nix | \
    sh -s -- install linux --init none --no-confirm
fi

Issue: Fish config assumes tools exist

# ❌ BAD
eval (starship init fish)

# ✅ GOOD
if type -q starship
  eval (starship init fish)
end

Output Format

Present findings as:

🔍 Compatibility Audit Results

🔴 Critical Issues (blocks installation)

• scripts/cleanup-symlinks.sh:104 - Hardcoded user path
  • Fix: Use $(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)
  • Applied: ✅ (auto-fixed via Edit tool)

🟡 Warnings (may fail on some platforms)

• install.sh:45 - Missing Alpine Linux detection
  • Fix: Add fallback for unknown Linux distros
  • Applied: ⏭️ (requires user decision on fallback behavior)

🟢 Suggestions (improvements)

• Consider adding WSL2 detection in CI
• Add Alpine Docker test to matrix

🧪 Test Coverage

• ✅ macOS (Intel + ARM) - CI native
• ✅ Ubuntu 25.04 - CI Docker
• ✅ Fedora 40 - CI Docker
• ❌ Alpine/musl - Not tested
• ❌ WSL2 - Not tested

📦 Nix Flake Status

• Last updated: 2025-01-15 (commit 4160763d74f6)
• Platforms: 4/4 building successfully
• Action: Run nix flake update + test matrix

Integration with Repository Workflow

Pre-commit checks:

# Add to git pre-commit hook
scripts/audit-compatibility.sh || exit 1

PR checklist (from AGENTS.md):

• Cross-platform verified (macOS, Ubuntu, Fedora)
• No hardcoded paths or user-specific assumptions
• Tests updated in tests/docker-test-commands.fish
• make test-pre && make test-docker passing

Continuous monitoring:

• Run this skill after any flake.nix changes
• Run on schedule (weekly) to catch drift
• Run when CI fails on specific platform

Reference Files

Key compatibility files to monitor:

• install.sh - Main entry point, OS detection
• scripts/install-nix.sh - Container detection, Nix installer
• scripts/link-config.sh - Platform-specific paths (VSCode)
• scripts/cleanup-symlinks.sh - ⚠️ Known hardcoded path issue
• config/fish/conf.d/05-homebrew.fish - macOS Homebrew detection
• config/fish/conf.d/10-nix.fish - Nix environment setup
• flake.nix - Package definitions for all platforms
• .github/workflows/ci.yml - CI test matrix
• tests/docker-test-commands.fish - Functional test suite

Error Recovery

If auto-fix breaks something:

1. Git tracks all changes → git diff to review
2. Backups created by scripts (.bak files)
3. Rollback: git checkout -- <file>
4. Re-run tests: make test-pre && make test-local

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Remember: This repository prioritizes reproducibility via Nix and testing via Docker. Every fix must pass the full test matrix before commit.