fix: add IndexError guard and error handling test

tests/test_search.py

@@ -2,6 +2,8 @@ import tempfile
 from pathlib import Path
 from unittest.mock import MagicMock, patch
 
+import pytest
+
 from companion.rag.search import SearchEngine
 from companion.rag.vector_store import VectorStore
 
@@ -32,3 +34,24 @@ def test_search_returns_results(mock_embedder_cls):
         results = engine.search("hello")
         assert len(results) == 1
         assert results[0]["source_file"] == "a.md"
+
+
+@patch("companion.rag.search.OllamaEmbedder")
+def test_search_raises_on_embedder_failure(mock_embedder_cls):
+    mock_embedder = MagicMock()
+    mock_embedder.embed.side_effect = RuntimeError("Connection failed")
+    mock_embedder_cls.return_value = mock_embedder
+
+    with tempfile.TemporaryDirectory() as tmp:
+        store = VectorStore(uri=tmp, dimensions=4)
+        engine = SearchEngine(
+            vector_store=store,
+            embedder_base_url="http://localhost:11434",
+            embedder_model="dummy",
+            embedder_batch_size=32,
+            default_top_k=5,
+            similarity_threshold=0.0,
+            hybrid_search_enabled=False,
+        )
+        with pytest.raises(RuntimeError, match="Failed to generate embedding"):
+            engine.search("hello")