Implement search and reranking functionality with FTS and embedding support

- Added BaseReranker abstract class for defining reranking interfaces.
- Implemented FastEmbedReranker using fastembed's TextCrossEncoder for scoring document-query pairs.
- Introduced FTSEngine for full-text search capabilities using SQLite FTS5.
- Developed SearchPipeline to integrate embedding, binary search, ANN indexing, FTS, and reranking.
- Added fusion methods for combining results from different search strategies using Reciprocal Rank Fusion.
- Created unit and integration tests for the new search and reranking components.
- Established configuration management for search parameters and models.

codex-lens-v2/tests/integration/test_search_pipeline.py

@@ -0,0 +1,44 @@
+"""Integration tests for SearchPipeline using real components and mock embedder/reranker."""
+from __future__ import annotations
+
+
+def test_vector_search_returns_results(search_pipeline):
+    results = search_pipeline.search("authentication middleware")
+    assert len(results) > 0
+    assert all(isinstance(r.score, float) for r in results)
+
+
+def test_exact_keyword_search(search_pipeline):
+    results = search_pipeline.search("authenticate")
+    assert len(results) > 0
+    result_ids = {r.id for r in results}
+    # Doc 0 and 10 both contain "authenticate"
+    assert result_ids & {0, 10}, f"Expected doc 0 or 10 in results, got {result_ids}"
+
+
+def test_pipeline_top_k_limit(search_pipeline):
+    results = search_pipeline.search("user", top_k=5)
+    assert len(results) <= 5
+
+
+def test_search_result_fields_populated(search_pipeline):
+    results = search_pipeline.search("password")
+    assert len(results) > 0
+    for r in results:
+        assert r.id >= 0
+        assert r.score >= 0
+        assert isinstance(r.path, str)
+
+
+def test_empty_query_handled(search_pipeline):
+    results = search_pipeline.search("")
+    assert isinstance(results, list)  # no exception
+
+
+def test_different_queries_give_different_results(search_pipeline):
+    r1 = search_pipeline.search("authenticate user")
+    r2 = search_pipeline.search("cache redis")
+    # Results should differ (different top IDs or scores), unless both are empty
+    ids1 = [r.id for r in r1]
+    ids2 = [r.id for r in r2]
+    assert ids1 != ids2 or len(r1) == 0