diff --git a/tests/test_rag_store.py b/tests/test_rag_store.py
new file mode 100644
index 0000000..9889517
--- /dev/null
+++ b/tests/test_rag_store.py
@@ -0,0 +1,374 @@
+"""
+tests/test_rag_store.py
+=======================
+Unit tests for services/rag_store.py.
+
+All tests use mocked ChromaDB and Ollama dependencies — no external services
+or network access required.
+"""
+from __future__ import annotations
+
+import json
+import time
+import types
+from pathlib import Path
+from unittest.mock import MagicMock, patch, mock_open
+
+import pytest
+
+# ---------------------------------------------------------------------------
+# Helpers to reset module-level singletons between tests
+# ---------------------------------------------------------------------------
+
+def _reset_rag_module():
+    """Reset all module-level state in rag_store between tests."""
+    import services.rag_store as rs
+    rs._rag_ready = False
+    rs._chroma_client = None
+    rs._chroma_collection = None
+
+
+@pytest.fixture(autouse=True)
+def reset_rag_state():
+    _reset_rag_module()
+    yield
+    _reset_rag_module()
+
+
+# ---------------------------------------------------------------------------
+# _build_document
+# ---------------------------------------------------------------------------
+
+class TestBuildDocument:
+    def test_includes_all_four_fields(self):
+        from services.rag_store import _build_document
+        card = {
+            "name": "Rampant Growth",
+            "mana_cost": "{1}{G}",
+            "type_line": "Sorcery",
+            "oracle_text": "Search your library for a basic land card.",
+        }
+        doc = _build_document(card)
+        assert "Rampant Growth" in doc
+        assert "{1}{G}" in doc
+        assert "Sorcery" in doc
+        assert "Search your library" in doc
+
+    def test_mana_cost_present_in_document(self):
+        """Regression: mana_cost was previously missing (bug #128)."""
+        from services.rag_store import _build_document
+        card = {"name": "Lightning Bolt", "mana_cost": "{R}", "type_line": "Instant", "oracle_text": "Deal 3 damage."}
+        doc = _build_document(card)
+        assert "{R}" in doc
+
+    def test_missing_mana_cost_skipped(self):
+        from services.rag_store import _build_document
+        card = {"name": "Plains", "mana_cost": "", "type_line": "Basic Land", "oracle_text": ""}
+        doc = _build_document(card)
+        # Should not produce " |  | " style empty fields
+        assert "Plains" in doc
+        assert doc.count(" |  | ") == 0
+
+    def test_empty_card_returns_name_only(self):
+        from services.rag_store import _build_document
+        card = {"name": "Unnamed"}
+        doc = _build_document(card)
+        assert doc == "Unnamed"
+
+    def test_pipe_delimiter_format(self):
+        from services.rag_store import _build_document
+        card = {"name": "A", "mana_cost": "B", "type_line": "C", "oracle_text": "D"}
+        assert _build_document(card) == "A | B | C | D"
+
+
+# ---------------------------------------------------------------------------
+# _build_metadata
+# ---------------------------------------------------------------------------
+
+class TestBuildMetadata:
+    def test_color_identity_json_string_parsed(self):
+        from services.rag_store import _build_metadata
+        card = {"name": "X", "color_identity": '["W", "U"]', "cmc": 3}
+        meta = _build_metadata(card)
+        assert meta["color_identity"] == "U,W"  # sorted
+
+    def test_color_identity_list_input(self):
+        from services.rag_store import _build_metadata
+        card = {"name": "X", "color_identity": ["B", "G"], "cmc": 2}
+        meta = _build_metadata(card)
+        assert meta["color_identity"] == "B,G"
+
+    def test_colorless_card(self):
+        from services.rag_store import _build_metadata
+        card = {"name": "Sol Ring", "color_identity": "[]", "cmc": 1}
+        meta = _build_metadata(card)
+        assert meta["color_identity"] == ""
+
+    def test_malformed_color_identity_defaults_empty(self):
+        from services.rag_store import _build_metadata
+        card = {"name": "X", "color_identity": "not-json", "cmc": 0}
+        meta = _build_metadata(card)
+        assert meta["color_identity"] == ""
+
+    def test_cmc_none_defaults_zero(self):
+        from services.rag_store import _build_metadata
+        card = {"name": "X", "cmc": None}
+        meta = _build_metadata(card)
+        assert meta["cmc"] == 0.0
+
+
+# ---------------------------------------------------------------------------
+# _read_build_meta / _write_build_meta
+# ---------------------------------------------------------------------------
+
+class TestBuildMeta:
+    def test_write_then_read_roundtrip(self, tmp_path):
+        import services.rag_store as rs
+        original_dir = rs.RAG_CHROMA_DIR
+        original_path = rs.BUILD_META_PATH
+        try:
+            rs.RAG_CHROMA_DIR = tmp_path
+            rs.BUILD_META_PATH = tmp_path / "build_meta.json"
+            rs._write_build_meta(card_count=12345)
+            meta = rs._read_build_meta()
+            assert meta["card_count"] == 12345
+            assert abs(meta["built_at"] - time.time()) < 5
+        finally:
+            rs.RAG_CHROMA_DIR = original_dir
+            rs.BUILD_META_PATH = original_path
+
+    def test_read_missing_returns_empty_dict(self, tmp_path):
+        import services.rag_store as rs
+        original_path = rs.BUILD_META_PATH
+        try:
+            rs.BUILD_META_PATH = tmp_path / "nonexistent.json"
+            assert rs._read_build_meta() == {}
+        finally:
+            rs.BUILD_META_PATH = original_path
+
+
+# ---------------------------------------------------------------------------
+# _collection_is_current
+# ---------------------------------------------------------------------------
+
+class TestCollectionIsCurrent:
+    def _make_collection(self, count: int) -> MagicMock:
+        col = MagicMock()
+        col.count.return_value = count
+        return col
+
+    def test_empty_collection_returns_false(self):
+        from services.rag_store import _collection_is_current
+        col = self._make_collection(0)
+        assert _collection_is_current(col, 1000) is False
+
+    def test_current_collection_returns_true(self, tmp_path):
+        import services.rag_store as rs
+        original_path = rs.BUILD_META_PATH
+        try:
+            rs.BUILD_META_PATH = tmp_path / "build_meta.json"
+            rs._write_build_meta(card_count=1000)
+            col = self._make_collection(1000)
+            assert rs._collection_is_current(col, 1000) is True
+        finally:
+            rs.BUILD_META_PATH = original_path
+
+    def test_stale_by_age_returns_false(self, tmp_path):
+        import services.rag_store as rs
+        original_path = rs.BUILD_META_PATH
+        try:
+            rs.BUILD_META_PATH = tmp_path / "build_meta.json"
+            # Write a built_at 15 days ago
+            rs.BUILD_META_PATH.write_text(
+                json.dumps({"built_at": time.time() - (15 * 86400), "card_count": 1000}),
+                encoding="utf-8",
+            )
+            col = self._make_collection(1000)
+            assert rs._collection_is_current(col, 1000) is False
+        finally:
+            rs.BUILD_META_PATH = original_path
+
+    def test_count_mismatch_returns_false(self, tmp_path):
+        import services.rag_store as rs
+        original_path = rs.BUILD_META_PATH
+        try:
+            rs.BUILD_META_PATH = tmp_path / "build_meta.json"
+            rs._write_build_meta(card_count=500)
+            col = self._make_collection(500)   # chroma has 500
+            assert rs._collection_is_current(col, 1000) is False  # bulk has 1000
+        finally:
+            rs.BUILD_META_PATH = original_path
+
+
+# ---------------------------------------------------------------------------
+# query_cards
+# ---------------------------------------------------------------------------
+
+class TestQueryCards:
+    def test_returns_empty_when_not_ready(self):
+        from services.rag_store import query_cards
+        # _rag_ready is False (reset by fixture)
+        result = query_cards("draw cards")
+        assert result == []
+
+    def test_color_filter_removes_off_color_cards(self):
+        import services.rag_store as rs
+        rs._rag_ready = True
+
+        mock_col = MagicMock()
+        mock_col.query.return_value = {
+            "ids": [["id1", "id2"]],
+            "documents": [["Wrath | {3}{W}{W} | Sorcery | Destroy all", "Dark Ritual | {B} | Instant | Add BBB"]],
+            "metadatas": [[
+                {"name": "Wrath", "type_line": "Sorcery", "color_identity": "W", "cmc": 5.0, "mana_cost": "{3}{W}{W}"},
+                {"name": "Dark Ritual", "type_line": "Instant", "color_identity": "B", "cmc": 1.0, "mana_cost": "{B}"},
+            ]],
+            "distances": [[0.1, 0.2]],
+        }
+        rs._chroma_collection = mock_col
+
+        results = rs.query_cards("mana acceleration", n_results=10, color_identity=["W"])
+        names = [r["name"] for r in results]
+        assert "Wrath" in names
+        assert "Dark Ritual" not in names
+
+    def test_distance_converted_to_score_in_route(self):
+        """Verify distance field is present and in [0, 1] range."""
+        import services.rag_store as rs
+        rs._rag_ready = True
+
+        mock_col = MagicMock()
+        mock_col.query.return_value = {
+            "ids": [["id1"]],
+            "documents": [["Sol Ring | {1} | Artifact | Add two colorless mana."]],
+            "metadatas": [[
+                {"name": "Sol Ring", "type_line": "Artifact", "color_identity": "", "cmc": 1.0, "mana_cost": "{1}"},
+            ]],
+            "distances": [[0.15]],
+        }
+        rs._chroma_collection = mock_col
+
+        results = rs.query_cards("mana rock", n_results=1)
+        assert len(results) == 1
+        assert results[0]["distance"] == 0.15
+        assert results[0]["name"] == "Sol Ring"
+
+    def test_empty_chroma_result_returns_empty_list(self):
+        import services.rag_store as rs
+        rs._rag_ready = True
+
+        mock_col = MagicMock()
+        mock_col.query.return_value = {"ids": [[]], "documents": [[]], "metadatas": [[]], "distances": [[]]}
+        rs._chroma_collection = mock_col
+
+        assert rs.query_cards("nothing") == []
+
+
+# ---------------------------------------------------------------------------
+# get_rag_stats
+# ---------------------------------------------------------------------------
+
+class TestGetRagStats:
+    def test_returns_expected_keys(self):
+        import services.rag_store as rs
+        mock_col = MagicMock()
+        mock_col.count.return_value = 42000
+        rs._chroma_collection = mock_col
+
+        stats = rs.get_rag_stats()
+        for key in ["ready", "chroma_dir", "embedding_model", "ollama_url", "card_count", "built_at", "age_days"]:
+            assert key in stats, f"Missing key: {key}"
+
+    def test_card_count_from_collection(self):
+        import services.rag_store as rs
+        mock_col = MagicMock()
+        mock_col.count.return_value = 55000
+        rs._chroma_collection = mock_col
+
+        stats = rs.get_rag_stats()
+        assert stats["card_count"] == 55000
+
+    def test_ready_false_when_not_initialized(self):
+        from services.rag_store import get_rag_stats
+        stats = get_rag_stats()
+        assert stats["ready"] is False
+
+
+# ---------------------------------------------------------------------------
+# build_index (public API for POST /api/rag/build)
+# ---------------------------------------------------------------------------
+
+class TestBuildIndex:
+    def test_skips_rebuild_when_current(self, tmp_path):
+        import services.rag_store as rs
+        original_path = rs.BUILD_META_PATH
+        original_dir = rs.RAG_CHROMA_DIR
+        try:
+            rs.BUILD_META_PATH = tmp_path / "build_meta.json"
+            rs.RAG_CHROMA_DIR = tmp_path
+            rs._write_build_meta(card_count=1000)
+
+            mock_col = MagicMock()
+            mock_col.count.return_value = 1000
+            rs._chroma_collection = mock_col
+
+            with patch("services.rag_store._get_collection", return_value=mock_col), \
+                 patch("services.scryfall_bulk.get_stats", return_value={"card_count": 1000}):
+                result = rs.build_index(force=False)
+
+            assert result.get("skipped") is True
+        finally:
+            rs.BUILD_META_PATH = original_path
+            rs.RAG_CHROMA_DIR = original_dir
+
+    def test_force_triggers_rebuild(self, tmp_path):
+        import services.rag_store as rs
+        with patch("services.rag_store._build_collection_from_bulk") as mock_build:
+            mock_build.return_value = {"indexed": 500, "failed": 0}
+            result = rs.build_index(force=True, batch_size=250)
+            mock_build.assert_called_once_with(batch_size=250)
+            assert result["indexed"] == 500
+            assert rs._rag_ready is True
+
+
+# ---------------------------------------------------------------------------
+# Failure tracking in _build_collection_from_bulk
+# ---------------------------------------------------------------------------
+
+class TestBuildCollectionFailureTracking:
+    def test_high_failure_rate_raises_runtime_error(self, tmp_path):
+        """If >1% of batches fail, a RuntimeError should be raised."""
+        import services.rag_store as rs
+
+        fake_rows = [
+            {"name": f"Card {i}", "oracle_text": "text", "type_line": "Instant",
+             "mana_cost": "{1}", "cmc": 1, "color_identity": "[]",
+             "rarity": "common", "scryfall_id": f"id-{i}"}
+            for i in range(200)
+        ]
+
+        mock_conn = MagicMock()
+        mock_cursor = MagicMock()
+        mock_cursor.fetchall.return_value = [types.SimpleNamespace(**r) for r in fake_rows]
+        mock_conn.execute.return_value = mock_cursor
+
+        mock_collection = MagicMock()
+        mock_collection.add.side_effect = Exception("Ollama timeout")
+
+        mock_client = MagicMock()
+        mock_client.create_collection.return_value = mock_collection
+
+        original_dir = rs.RAG_CHROMA_DIR
+        original_path = rs.BUILD_META_PATH
+        try:
+            rs.RAG_CHROMA_DIR = tmp_path
+            rs.BUILD_META_PATH = tmp_path / "build_meta.json"
+            with patch("services.scryfall_bulk.get_bulk_db", return_value=mock_conn), \
+                 patch("services.rag_store._get_chromadb_client", return_value=mock_client), \
+                 patch("services.rag_store._get_ollama_embedding_fn", return_value=MagicMock()), \
+                 patch("services.rag_store._invalidate_collection_singleton"):
+                with pytest.raises(RuntimeError, match="RAG build aborted"):
+                    rs._build_collection_from_bulk(batch_size=50)
+        finally:
+            rs.RAG_CHROMA_DIR = original_dir
+            rs.BUILD_META_PATH = original_path