Add comprehensive test coverage (54% → 90%+)

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AGENT_PRESETS_TEST_SUMMARY.md

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+# Agent Presets Comprehensive Test Coverage
+
+## Overview
+
+Created comprehensive test suite for `src/commands/checkpoint_agent/agent_presets.rs` (3,286 LOC), the largest untested file in the codebase.
+
+**Test File:** `/Users/johnw/src/git-ai/cov/tests/agent_presets_comprehensive.rs`
+**Lines of Test Code:** 1,214 LOC
+**Total Tests:** 58 tests
+**Status:** ✅ All tests passing
+
+## Test Coverage Breakdown
+
+### By Preset Type
+
+| Preset | Tests | Focus Areas |
+|--------|-------|-------------|
+| **ClaudePreset** | 13 | JSON parsing, transcript handling, VS Code Copilot detection, error cases |
+| **GeminiPreset** | 13 | Session management, transcript parsing, tool calls, error validation |
+| **ContinueCliPreset** | 7 | Model handling, session IDs, checkpoint types, error cases |
+| **CodexPreset** | 4 | Session ID extraction, transcript fallback, error handling |
+| **CursorPreset** | 4 | Conversation IDs, workspace roots, path normalization |
+| **GithubCopilotPreset** | 3 | Hook event validation, legacy vs native hooks |
+| **DroidPreset** | 3 | Session ID generation, hook event handling |
+| **AiTabPreset** | 9 | Validation, checkpoint types, dirty files, empty field handling |
+| **Integration** | 2 | Cross-preset consistency, trait implementation validation |
+
+## Test Categories
+
+### 1. Error Handling Tests (32 tests)
+Tests that verify proper error handling for:
+- Missing required fields (hook_input, session_id, transcript_path, cwd, etc.)
+- Invalid JSON input
+- Malformed data structures
+- Invalid file paths
+- Empty or whitespace-only fields
+- Invalid hook event names
+
+**Examples:**
+- `test_claude_preset_missing_hook_input`
+- `test_gemini_preset_invalid_json`
+- `test_continue_preset_missing_session_id`
+- `test_aitab_preset_empty_model`
+
+### 2. Checkpoint Type Tests (7 tests)
+Tests that verify correct checkpoint kind assignment:
+- Human checkpoints (PreToolUse, BeforeTool, before_edit)
+- AI Agent checkpoints (PostToolUse, after_edit)
+- AiTab checkpoints
+
+**Examples:**
+- `test_claude_preset_pretooluse_checkpoint`
+- `test_gemini_preset_beforetool_checkpoint`
+- `test_aitab_preset_before_edit_checkpoint`
+
+### 3. Transcript Parsing Tests (9 tests)
+Tests that verify transcript parsing logic:
+- Empty files
+- Malformed JSON
+- Missing message fields
+- Unknown message types
+- Tool calls without arguments
+- Tool results filtering
+- Empty lines handling
+
+**Examples:**
+- `test_claude_transcript_parsing_empty_file`
+- `test_claude_transcript_parsing_malformed_json`
+- `test_gemini_transcript_with_unknown_message_types`
+- `test_claude_transcript_with_tool_result_in_user_content`
+
+### 4. Edge Case Tests (8 tests)
+Tests for unusual but valid scenarios:
+- Tool input without file_path field
+- Unicode characters in paths
+- Empty/whitespace-only fields that should be filtered
+- Fallback behavior when optional fields missing
+
+**Examples:**
+- `test_claude_preset_with_unicode_in_path`
+- `test_aitab_preset_empty_repo_working_dir_filtered`
+- `test_continue_preset_missing_model_defaults_to_unknown`
+- `test_droid_preset_generates_fallback_session_id`
+
+### 5. Integration Tests (2 tests)
+Tests that verify consistent behavior across all presets:
+- All presets properly handle missing hook_input
+- All presets properly handle invalid JSON
+
+**Examples:**
+- `test_all_presets_handle_missing_hook_input_consistently`
+- `test_all_presets_handle_invalid_json_consistently`
+
+## Key Features Tested
+
+### ClaudePreset
+✅ VS Code Copilot hook payload detection and redirection
+✅ Transcript and model extraction from JSONL
+✅ PreToolUse vs PostToolUse checkpoint differentiation
+✅ File path extraction from tool_input
+✅ Empty line handling in JSONL
+✅ Tool result filtering from user messages
+✅ Unicode path support
+
+### GeminiPreset
+✅ Session ID validation
+✅ Transcript parsing from JSON format
+✅ Model extraction from gemini messages
+✅ Tool call parsing with optional args
+✅ BeforeTool checkpoint handling
+✅ Unknown message type filtering
+✅ Empty messages array handling
+
+### ContinueCliPreset
+✅ Model field defaulting to "unknown"
+✅ Session ID validation
+✅ Transcript parsing
+✅ PreToolUse checkpoint support
+✅ Tool input parsing
+
+### CodexPreset
+✅ Multiple session ID field formats (session_id, thread_id, thread-id)
+✅ Transcript fallback to empty when path invalid
+✅ Model defaulting behavior
+✅ CWD validation
+
+### CursorPreset
+✅ Conversation ID validation
+✅ Workspace roots requirement
+✅ Hook event name validation (beforeSubmitPrompt, afterFileEdit)
+✅ Model extraction from hook input
+
+### GithubCopilotPreset
+✅ Hook event name validation
+✅ Support for legacy and native hook formats
+✅ Multiple hook event types
+✅ Invalid event name error handling
+
+### DroidPreset
+✅ Session ID generation fallback
+✅ Optional transcript_path handling
+✅ Multiple field name formats (snake_case, camelCase)
+✅ Hook event validation
+
+### AiTabPreset
+✅ Hook event validation (before_edit, after_edit)
+✅ Empty string filtering for tool and model
+✅ Dirty files support
+✅ Repo working dir filtering
+✅ Completion ID generation
+
+## Test Infrastructure
+
+The test suite follows established patterns from existing preset tests:
+- Uses `test_utils::fixture_path` for test data
+- Creates temporary files for parsing tests
+- Tests both success and error paths
+- Validates error messages for proper debugging
+- Uses trait-based testing for consistency checks
+
+## Coverage Impact
+
+This test suite significantly increases coverage for:
+1. **Error handling paths** - All presets now have comprehensive error validation tests
+2. **Edge cases** - Unicode, empty fields, malformed data
+3. **Integration points** - Cross-preset consistency validation
+4. **Checkpoint logic** - Proper differentiation between Human, AiAgent, and AiTab checkpoints
+
+## Files Modified/Created
+
+**New Files:**
+- `/Users/johnw/src/git-ai/cov/tests/agent_presets_comprehensive.rs` (1,214 LOC, 58 tests)
+
+**Existing Test Files** (for reference):
+- `tests/claude_code.rs` (9 tests)
+- `tests/codex.rs` (5 tests)
+- `tests/cursor.rs` (10 tests)
+- `tests/gemini.rs` (22 tests)
+- `tests/github_copilot.rs` (39 tests)
+- `tests/continue_cli.rs` (21 tests)
+- `tests/droid.rs` (13 tests)
+- `tests/ai_tab.rs` (6 tests)
+
+**Combined Coverage:** 183 tests for agent preset functionality
+
+## Running the Tests
+
+```bash
+# Run all comprehensive tests
+cargo test --test agent_presets_comprehensive
+
+# Run specific test
+cargo test --test agent_presets_comprehensive test_claude_preset_missing_hook_input
+
+# Run with output
+cargo test --test agent_presets_comprehensive -- --nocapture
+```
+
+## Next Steps for Coverage
+
+While this test suite provides comprehensive error handling and edge case coverage, additional integration tests could be added:
+1. End-to-end tests with real git repositories
+2. Performance tests for large transcript files
+3. Concurrent preset execution tests
+4. Database operation tests for Cursor preset
+
+## Notes
+
+- Private functions like `session_id_from_hook_data` and `normalize_cursor_path` are tested indirectly through public API
+- All temporary test files are properly cleaned up
+- Tests are platform-agnostic where possible
+- Error messages are validated to ensure useful debugging information