feat(codex-lens): add unified reranker architecture and file watcher

Unified Reranker Architecture:
- Add BaseReranker ABC with factory pattern
- Implement 4 backends: ONNX (default), API, LiteLLM, Legacy
- Add .env configuration parsing for API credentials
- Migrate from sentence-transformers to optimum+onnxruntime

File Watcher Module:
- Add real-time file system monitoring with watchdog
- Implement IncrementalIndexer for single-file updates
- Add WatcherManager with signal handling and graceful shutdown
- Add 'codexlens watch' CLI command
- Event filtering, debouncing, and deduplication
- Thread-safe design with proper resource cleanup

Tests: 16 watcher tests + 5 reranker test files

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

codex-lens/tests/test_watcher/test_file_watcher.py

@@ -0,0 +1,124 @@
+"""Tests for FileWatcher class."""
+
+from __future__ import annotations
+
+import time
+from pathlib import Path
+from typing import List
+
+import pytest
+
+from codexlens.watcher import FileWatcher, WatcherConfig, FileEvent, ChangeType
+
+
+class TestFileWatcherInit:
+    """Tests for FileWatcher initialization."""
+    
+    def test_init_with_valid_path(self, temp_project: Path, watcher_config: WatcherConfig):
+        """Test initializing with valid path."""
+        events: List[FileEvent] = []
+        watcher = FileWatcher(temp_project, watcher_config, lambda e: events.extend(e))
+        
+        assert watcher.root_path == temp_project.resolve()
+        assert watcher.config == watcher_config
+        assert not watcher.is_running
+    
+    def test_start_with_invalid_path(self, watcher_config: WatcherConfig):
+        """Test starting watcher with non-existent path."""
+        events: List[FileEvent] = []
+        watcher = FileWatcher(Path("/nonexistent/path"), watcher_config, lambda e: events.extend(e))
+        
+        with pytest.raises(ValueError, match="does not exist"):
+            watcher.start()
+
+
+class TestFileWatcherLifecycle:
+    """Tests for FileWatcher start/stop lifecycle."""
+    
+    def test_start_stop(self, temp_project: Path, watcher_config: WatcherConfig):
+        """Test basic start and stop."""
+        events: List[FileEvent] = []
+        watcher = FileWatcher(temp_project, watcher_config, lambda e: events.extend(e))
+        
+        watcher.start()
+        assert watcher.is_running
+        
+        watcher.stop()
+        assert not watcher.is_running
+    
+    def test_double_start(self, temp_project: Path, watcher_config: WatcherConfig):
+        """Test calling start twice."""
+        events: List[FileEvent] = []
+        watcher = FileWatcher(temp_project, watcher_config, lambda e: events.extend(e))
+        
+        watcher.start()
+        watcher.start()  # Should not raise
+        assert watcher.is_running
+        
+        watcher.stop()
+    
+    def test_double_stop(self, temp_project: Path, watcher_config: WatcherConfig):
+        """Test calling stop twice."""
+        events: List[FileEvent] = []
+        watcher = FileWatcher(temp_project, watcher_config, lambda e: events.extend(e))
+        
+        watcher.start()
+        watcher.stop()
+        watcher.stop()  # Should not raise
+        assert not watcher.is_running
+
+
+class TestFileWatcherEvents:
+    """Tests for FileWatcher event detection."""
+    
+    def test_detect_file_creation(self, temp_project: Path, watcher_config: WatcherConfig):
+        """Test detecting new file creation."""
+        events: List[FileEvent] = []
+        watcher = FileWatcher(temp_project, watcher_config, lambda e: events.extend(e))
+
+        try:
+            watcher.start()
+            time.sleep(0.3)  # Let watcher start (longer for Windows)
+
+            # Create new file
+            new_file = temp_project / "new_file.py"
+            new_file.write_text("# New file\n")
+
+            # Wait for event with retries (watchdog timing varies by platform)
+            max_wait = 2.0
+            waited = 0.0
+            while waited < max_wait:
+                time.sleep(0.2)
+                waited += 0.2
+                # Windows may report MODIFIED instead of CREATED
+                file_events = [e for e in events if e.change_type in (ChangeType.CREATED, ChangeType.MODIFIED)]
+                if any(e.path.name == "new_file.py" for e in file_events):
+                    break
+
+            # Check event was detected (Windows may report MODIFIED instead of CREATED)
+            relevant_events = [e for e in events if e.change_type in (ChangeType.CREATED, ChangeType.MODIFIED)]
+            assert len(relevant_events) >= 1, f"Expected file event, got: {events}"
+            assert any(e.path.name == "new_file.py" for e in relevant_events)
+        finally:
+            watcher.stop()
+    
+    def test_filter_ignored_directories(self, temp_project: Path, watcher_config: WatcherConfig):
+        """Test that files in ignored directories are filtered."""
+        events: List[FileEvent] = []
+        watcher = FileWatcher(temp_project, watcher_config, lambda e: events.extend(e))
+        
+        try:
+            watcher.start()
+            time.sleep(0.1)
+            
+            # Create file in .git (should be ignored)
+            git_file = temp_project / ".git" / "test.py"
+            git_file.write_text("# In git\n")
+            
+            time.sleep(watcher_config.debounce_ms / 1000.0 + 0.2)
+            
+            # No events should be detected for .git files
+            git_events = [e for e in events if ".git" in str(e.path)]
+            assert len(git_events) == 0
+        finally:
+            watcher.stop()