Fix Git detached HEAD branch switching failures with robust GitOperations module

[Copilot]

Problem

Git operations in the Cresta Open Data repository were failing when in detached HEAD state, producing the error:

[12:36:49] Git操作を開始します...
[12:36:49] 現在のブランチを確認中...
[12:36:49] detached HEAD状態を検出、mainブランチに切り替えます...
[12:36:49] ❌ ブランチ切り替えエラー: error: pathspec 'main' did not match any file(s) known to git

The core issue was that simple git checkout main and git checkout master commands would fail when:

• The repository was in detached HEAD state
• Local branches weren't properly synchronized with remote branches
• Branch names didn't match expectations

Solution

This PR introduces a comprehensive GitOperations module that provides robust Git operations with intelligent branch management:

Key Features

🔍 Dynamic Branch Detection

• Automatically detects both local and remote branches
• Uses git branch --format=%(refname:short) for reliable branch listing
• Handles edge cases like detached HEAD states

⚡ Priority-Based Branch Selection

• Implements smart branch selection: main → master → develop → first available
• Automatically finds the best branch to switch to based on availability

🔧 Automatic Branch Creation

• Creates local branches from remote when needed using git fetch origin branch:branch
• Falls back to creating new branches when none exist
• Handles upstream configuration automatically

📋 Comprehensive Error Handling

• Detailed logging with timestamps for debugging
• Timeout protection (30 seconds per Git command)
• Graceful error recovery and meaningful error messages

🚀 Detached HEAD Recovery

• Automatically detects detached HEAD state
• Finds appropriate target branch and switches seamlessly
• Continues with Git operations without manual intervention

Usage Examples

from git_operations import GitOperations

# Basic usage - handles all edge cases automatically
git_ops = GitOperations()
success = git_ops.execute_git_push("Fix important issue")

# Test branch switching capability
git_ops.ensure_branch_available("main")
git_ops.switch_to_branch("main")

# Command line usage
python3 git_operations.py --message "Update data files"
python3 git_operations.py --test-branch main

Demonstration

The fix successfully handles the original error scenario:

# Before: Failed with "pathspec 'main' did not match any file(s) known to git"
# After: Successful automated recovery
[03:50:22] detached HEAD状態を検出、適切なブランチに切り替えます...
[03:50:22] リモートブランチをフェッチ中...
[03:50:22] ✅ リモートブランチのフェッチが完了しました
[03:50:22] 優先ブランチ 'main' が見つかりました
[03:50:22] ✅ ブランチ 'main' に正常に切り替えました
[03:50:22] ✅ コミットが完了しました

Files Added

• git_operations.py - Main GitOperations class with robust Git handling
• test_git_operations.py - Comprehensive test suite
• README_git_ops.md - Detailed documentation and usage guide
• demo_results.md - Demonstration of the fix in action
• .gitignore - Proper repository hygiene

Testing

The solution includes a full test suite that validates:

• Branch detection in various repository states
• Successful branch switching from detached HEAD
• Error handling and recovery scenarios
• Integration with existing Git workflows

This fix ensures that Git operations will work reliably regardless of the repository state, eliminating the detached HEAD branch switching failures that were blocking development workflows.

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