ci(e2e): implement comprehensive cross-platform E2E testing infrastructure

[wherka-ama]

Description

Implements comprehensive cross-platform end-to-end (E2E) testing infrastructure to validate all released artifacts before promotion to latest. This PR addresses the need for automated testing across multiple OS/architecture combinations to ensure release quality.

Key Objectives:

1. Prerelease gate pattern: Upload as prerelease → run E2E → promote to latest on success
2. Package-specific test jobs: Separate jobs for .deb, .rpm, and archive formats
3. Standalone validation: Test that /usr/bin/gh-app-auth works without gh CLI
4. Cross-platform coverage: AMD64 and ARM64 for Linux, macOS, and Windows

Closes #39

Type of Change

Please delete options that are not relevant:

• 🐛 Bug fix (non-breaking change which fixes an issue)
• ✨ New feature (non-breaking change which adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected)
• 📚 Documentation update
• 🔧 Refactoring (no functional changes, no api changes)
• ⚡ Performance improvements
• 🧪 Test updates
• 🔒 Security improvements

Changes Made

E2E Workflow (.github/workflows/e2e.yml)

• Added 10 platform-specific E2E jobs covering all release artifacts
• Linux AMD64/ARM64 binary tests
• Fedora AMD64/ARM64 RPM package tests (container-based)
• Ubuntu AMD64/ARM64 DEB package tests (container-based)
• macOS AMD64 (macos-15-intel) and ARM64 (macos-latest) binary tests
• Windows AMD64 (windows-latest) and ARM64 (windows-11-arm) binary tests
• Promote-release job that gates latest release on all E2E jobs passing

Code Fixes

• cmd/setup.go: Skip Unix permission checks on Windows (Windows uses ACLs, not Unix mode bits)
• cmd/gitconfig.go: Convert backslashes to forward slashes in Windows credential helper batch wrapper paths (prevents shell interpretation issues)

Build & Packaging

• nfpm.yaml: New nfpm configuration for building .deb and .rpm packages
• Makefile: Added packaging targets (package, package-deb, package-rpm)
• .gitignore: Added packaging artifact patterns
• .github/workflows/release.yml: Updated to trigger E2E workflow after prerelease upload

E2E Test Infrastructure

• test/e2e/helpers_test.go: Added Windows temp dir helper for credential wrapper tests
• test/e2e/suite_test.go: Updated test configuration for multi-platform support
• test/e2e/auth_test.go: Enhanced authentication tests with proper binary path handling
• test/e2e/gitops_test.go: Streamlined Git operations tests
• test/e2e/install_test.go: Fixed install path verification for packaged binaries

Testing

Please describe the tests that you ran to verify your changes:

• Unit tests pass: go test ./...
• Build succeeds: go build -o gh-app-auth .
• Manual testing performed
• Integration tests with real GitHub Apps (via E2E workflow)

Test Configuration

• OS: Multiple (Ubuntu, Fedora, macOS, Windows)
• Go version: 1.21+
• GitHub CLI version: Latest

E2E Test Results:
All 10 platform jobs must pass before release promotion:

• ✅ Linux AMD64/ARM64 binaries
• ✅ Fedora AMD64/ARM64 RPM packages
• ✅ Ubuntu AMD64/ARM64 DEB packages
• ✅ macOS AMD64/ARM64 binaries
• ✅ Windows AMD64/ARM64 binaries

Security Considerations

If this PR involves security-related changes:

• No sensitive data (tokens, keys) exposed in code or tests
• Input validation added/reviewed for new functionality
• Private key handling follows security best practices
• Token caching security maintained
• No new attack vectors introduced

Notes:

• E2E tests use GitHub secrets (E2E_APP_ID, E2E_PRIVATE_KEY_B64, E2E_GITHUB_TOKEN)
• Private key file permissions properly validated on Unix (skipped on Windows)
• No secrets logged in plain text (uses secrets.HashToken() for debug output)

Documentation

• Code comments updated
• README.md updated (if needed)
• Architecture documentation updated (if needed)
• Command help text updated (if needed)

Notes:

• E2E infrastructure documented in workflow file comments
• Test helper functions have inline documentation

Checklist

• My code follows the project's style guidelines
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published
• Commit messages follow Conventional Commits format
• PR title follows conventional commits format (e.g., ci(e2e): implement comprehensive cross-platform E2E testing)

Breaking Changes

If this is a breaking change, please describe the impact and migration path for existing users:

None - This PR only adds CI/CD infrastructure and does not change any user-facing functionality.

Additional Notes

Known Limitations

• Windows ARM64 runner (windows-11-arm) is in public preview
• macOS Intel runners (macos-15-intel) are deprecated as of Dec 2025, migration to ARM64 recommended for future

Future Work

• Consider adding FreeBSD or other Unix-like systems if needed
• Add performance benchmarking to E2E pipeline
• Implement E2E test result reporting to PR comments or the job summary

[codecov]

Codecov Report

❌ Patch coverage is 27.27273% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 54.66%. Comparing base (8f640ac) to head (70bb99e).
⚠️ Report is 19 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/gitconfig.go	11.11%	14 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #40      +/-   ##
==========================================
+ Coverage   54.29%   54.66%   +0.36%     
==========================================
  Files          27       27              
  Lines        3514     3635     +121     
==========================================
+ Hits         1908     1987      +79     
- Misses       1447     1485      +38     
- Partials      159      163       +4     

Flag	Coverage Δ
unittests	54.66% <27.27%> (+0.36%)	⬆️

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