## 1. Project Setup

- [ ] 1.1 Initialize Go module with proper imports
- [ ] 1.2 Add required dependencies (libalpm wrapper)
- [ ] 1.3 Set up project structure (main.go, pkg/ subdirectory)

## 2. Input Parsing

- [ ] 2.1 Implement stdin reader to collect package names
- [ ] 2.2 Implement state file reader for text-list format
- [ ] 2.3 Add whitespace normalization for package names
- [ ] 2.4 Create package name set data structure

## 3. Input Merging

- [ ] 3.1 Implement additive merging of stdin and state file packages
- [ ] 3.2 Handle multiple --state flags with last-writer-wins per file
- [ ] 3.3 Implement duplicate package handling (no deduplication)

## 4. State Validation

- [ ] 4.1 Implement empty state detection (no packages found)
- [ ] 4.2 Add stderr error output for empty state
- [ ] 4.3 Set exit code 1 for empty state case (abort, not proceed)

## 5. Pacman Integration

- [ ] 5.1 Implement pacman -Syu command execution wrapper
- [ ] 5.2 Add command-line argument construction with package list
- [ ] 5.3 Capture pacman stdout and stderr output
- [ ] 5.4 Implement pacman error message parsing
- [ ] 5.5 Handle pacman exit codes for success/failure detection
- [ ] 5.6 Verify pacman automatically resolves transitive dependencies
- [ ] 5.7 Verify shared dependencies are deduplicated by pacman

## 6. Explicit Marking & Orphan Cleanup

- [ ] 6.1 Get list of currently installed packages before sync
- [ ] 6.2 Mark declared state packages as explicitly installed via pacman -D --explicit
- [ ] 6.3 Run pacman sync operation (5.x series)
- [ ] 6.4 Run pacman -Rsu to remove orphaned packages
- [ ] 6.5 Capture and report number of packages removed
- [ ] 6.6 Handle case where no orphans exist (no packages removed)

## 7. AUR Integration

- [ ] 7.1 Implement AUR package lookup via package query (Jguer/aur)
- [ ] 7.2 Add pacman first attempt (package not in repos)
- [ ] 7.3 Implement AUR fallback using makepkg (direct build, not AUR helper)
- [ ] 7.4 Clone AUR package git repo to temp directory
- [ ] 7.5 Run makepkg -si in temp directory for installation
- [ ] 7.6 Add stderr error reporting for packages not in pacman or AUR
- [ ] 7.7 Capture makepkg stdout and stderr for output parsing
- [ ] 7.8 Handle makepkg exit codes for success/failure detection

## 8. Output Generation

- [ ] 8.1 Capture installed/removed package counts from pacman output
- [ ] 8.2 Generate machine-readable output line in requested format
- [ ] 8.3 Include error details in output on failure

## 9. CLI Interface

- [ ] 9.1 Implement --state flag argument parsing
- [ ] 9.2 Implement stdin input handling from /dev/stdin
- [ ] 9.3 Set up correct CLI usage/help message
- [ ] 9.4 Implement flag order validation

## 10. Integration & Testing

- [ ] 10.1 Wire together stdin -> state files -> merging -> validation -> pacman sync -> orphan cleanup -> output
- [ ] 10.2 Test empty state error output and exit code 1
- [ ] 10.3 Test single state file parsing
- [ ] 10.4 Test multiple state file merging
- [ ] 10.5 Test stdin input parsing
- [ ] 10.6 Test explicit marking before sync
- [ ] 10.7 Test pacman command execution with real packages
- [ ] 10.8 Test orphan cleanup removes unneeded packages
- [ ] 10.9 Test AUR fallback with makepkg for AUR package
- [ ] 10.10 Test error handling for missing packages
- [ ] 10.11 Generate final binary