fix: add error handling and docstrings to search engine

src/companion/rag/search.py

@@ -5,6 +5,22 @@ from companion.rag.vector_store import VectorStore
 
 
 class SearchEngine:
+    """Search engine for semantic search using vector embeddings.
+
+    Args:
+        vector_store: Vector store instance for searching
+        embedder_base_url: Base URL for the embedding service (Ollama)
+        embedder_model: Model name for embeddings
+        embedder_batch_size: Batch size for embedding requests
+        default_top_k: Default number of results to return
+        similarity_threshold: Maximum distance threshold for filtering results
+        hybrid_search_enabled: Reserved for future hybrid search implementation
+        keyword_weight: Reserved for future hybrid search (keyword component weight)
+        semantic_weight: Reserved for future hybrid search (semantic component weight)
+    """
+
+    _DISTANCE_FIELD = "_distance"
+
     def __init__(
         self,
         vector_store: VectorStore,
@@ -35,13 +51,34 @@ class SearchEngine:
         top_k: int | None = None,
         filters: dict[str, Any] | None = None,
     ) -> list[dict[str, Any]]:
+        """Search for relevant documents using semantic similarity.
+
+        Args:
+            query: The search query string
+            top_k: Number of results to return (defaults to default_top_k)
+            filters: Optional metadata filters to apply
+
+        Returns:
+            List of matching documents with similarity scores
+
+        Raises:
+            RuntimeError: If embedding generation fails
+        """
         k = top_k or self.default_top_k
+
+        try:
             query_embedding = self.embedder.embed([query])[0]
+        except RuntimeError as e:
+            raise RuntimeError(f"Failed to generate embedding for query: {e}") from e
+
         results = self.vector_store.search(query_embedding, top_k=k, filters=filters)
+
         if self.similarity_threshold > 0 and results:
             results = [
                 r
                 for r in results
-                if r.get("_distance", float("inf")) <= self.similarity_threshold
+                if r.get(self._DISTANCE_FIELD, float("inf"))
+                <= self.similarity_threshold
             ]
+
         return results