Enhanced Historical Functionality for All Storage Types and Complex Multi-Branch Testing

[zhangfengcdt]

This PR implements comprehensive historical functionality for all storage types (InMemory, File, RocksDB) by ensuring they
save tree configuration to git commits, and adds extensive multi-branch testing for the get_commits method. A critical bug in
branch isolation was also discovered and fixed during testing.

Key Changes

1. Universal Historical Functionality (src/git/versioned_store.rs)

Problem: Only GitNodeStorage had full historical functionality. Other storage types (InMemory, File, RocksDB) couldn't
provide historical access because they didn't save tree configuration to git commits.

Solution:

• Created TreeConfigSaver trait for polymorphic tree config saving
• Added specialized save_tree_config_to_git() implementations for each storage type:
  • GitNodeStorage: Saves both tree config AND hash mappings (required for git blob storage)
  • InMemory/File/RocksDB: Save tree config only (hash mappings not needed)
• Modified generic commit() method to call save_tree_config_to_git_internal() for all storage types

Impact: All storage types now support full historical functionality:

• get_keys_at_ref() - Get keys at any commit/branch
• diff() - Compare between commits/branches
• get_commits() - Track key change history
• get_commit_history() - Access commit metadata

2. Branch Isolation Bug Fix (src/git/versioned_store.rs)

Problem: Critical bug discovered during testing - when switching branches, data would leak between branches. Keys created on
feature branches would appear on main branch.

Solution:

• Added Git-specific checkout() method that properly reloads tree state
• Implemented reload_tree_from_head() to rebuild tree from target commit
• Fixed directory creation for branch names with slashes (e.g., feature/new-keys)

Impact: Perfect branch isolation - keys are now properly scoped to their respective branches.

3. Comprehensive Multi-Branch Testing (src/git/versioned_store.rs)

Added 4 new test suites covering complex real-world scenarios:

test_get_commits_complex_multi_branch_scenarios

• Multi-branch development with main, feature, and hotfix branches
• Key tracking across branches with different evolution paths
• Verifies branch isolation and correct commit history

test_get_commits_merge_scenarios

• Pre-merge testing with parallel development
• Branch-specific keys and shared key modifications
• Different evolution paths for same keys on different branches

test_get_commits_key_lifecycle_patterns

• Complete lifecycle: create → modify → delete (5 commits tracked)
• Delete and recreate scenarios (full history preserved)
• Static keys that never change

test_get_commits_empty_and_edge_cases

• Non-existent keys, empty repositories
• Binary keys/values, very long key names (1000+ chars)
• Empty values and edge cases

Test Results

• Before: 60 tests passing
• After: 64 tests passing (4 new comprehensive test suites)
• Coverage: All storage types now have identical historical functionality
• Branch isolation: ✅ Fixed - no data leakage between branches

Example Usage

// Now works for ALL storage types (not just Git)
let mut store = InMemoryVersionedKvStore::<32>::init(&path)?;

// Add data and commit
store.insert(b"key1".to_vec(), b"value1".to_vec()).unwrap();
let commit1 = store.commit("Add key1").unwrap();

// Create feature branch and modify key
store.create_branch("feature/enhancement").unwrap();
store.checkout("feature/enhancement").unwrap();
store.update(b"key1".to_vec(), b"new_value".to_vec()).unwrap();
let commit2 = store.commit("Update key1 on feature").unwrap();

// Historical access now works for all storage types
let commits = store.get_commits(b"key1").unwrap(); // Returns 2 commits
let diff = store.diff(&commit1.to_hex().to_string(), &commit2.to_hex().to_string()).unwrap();
let keys_at_head = store.get_keys_at_ref("HEAD").unwrap();

// Branch isolation - switching back to main
store.checkout("main").unwrap();
let main_commits = store.get_commits(b"key1").unwrap(); // Returns 1 commit (no feature changes)