Мempalace backend seam (#413)

* refactor: add stage-1 backend abstraction seam

Introduce the first upstreamable storage seam for MemPalace without
bringing in the PostgreSQL spike or any benchmark artifacts.

This change adds a small backend package with:
- BaseCollection as the minimal collection contract
- ChromaBackend/ChromaCollection as the default implementation

It then routes the main runtime collection consumers through that seam:
- palace.py
- searcher.py
- layers.py
- palace_graph.py
- mcp_server.py
- miner.status()

Behavioral constraints kept for stage 1:
- ChromaDB remains the only backend and the default path
- no config/env backend selection yet
- no PostgreSQL code
- no benchmark or research files
- existing tests stay unchanged

Important compatibility details:
- read paths now call the seam with create=False so they still surface
  the existing 'no palace found' behavior instead of silently creating
  empty collections
- write paths keep create=True semantics through palace.get_collection()
- layers/searcher retain a chromadb module attribute so the existing
  mock-based tests can keep patching PersistentClient unchanged
- ChromaBackend only creates palace directories on create=True, which
  preserves mocked read-path tests that use fake read-only paths

Verification:
- python3 -m py_compile mempalace/backends/__init__.py mempalace/backends/base.py mempalace/backends/chroma.py mempalace/palace.py mempalace/searcher.py mempalace/layers.py mempalace/palace_graph.py mempalace/mcp_server.py mempalace/miner.py
- pytest -q  # 529 passed, 106 deselected

* refactor: clean up stage-1 seam compatibility shims

Tighten the stage-1 backend abstraction branch after review.

This follow-up does three small things:
- keep the chromadb compatibility hook in searcher.py and layers.py,
  but express it through the backends.chroma module so it no longer
  reads like an accidental unused import
- fix the palace_graph.py helper alias to avoid the local name collision
  flagged by ruff (imported helper vs local _get_collection wrapper)
- preserve the existing mock-based test patch points unchanged while
  keeping the new backend seam intact

Why this matters:
- the direct  form looked like a
  dead import in review, even though it was intentionally preserving the
  existing test seam ( and
  )
- palace_graph.py had a real lint issue ( redefinition) that was
  small but worth fixing before a public PR

Verification:
- /opt/homebrew/bin/ruff check mempalace/backends/__init__.py mempalace/backends/base.py mempalace/backends/chroma.py mempalace/palace.py mempalace/searcher.py mempalace/layers.py mempalace/palace_graph.py mempalace/mcp_server.py mempalace/miner.py
- pytest -q tests/test_layers.py tests/test_searcher.py
- pytest -q  # 529 passed, 106 deselected

* docs: explain backend shim imports in search paths

Add short code comments in searcher.py and layers.py explaining why the
module-level `chromadb` alias remains after the stage-1 backend seam
refactor.

The alias is intentional: it preserves the existing mock patch points used
by the current test suite (`mempalace.searcher.chromadb.PersistentClient`
and `mempalace.layers.chromadb.PersistentClient`) while the runtime logic
now flows through the backend abstraction.

This keeps the public PR easier to review because the apparent "unused
import" now has an explicit reason next to it.

Verification:
- /opt/homebrew/bin/ruff check mempalace/searcher.py mempalace/layers.py
- pytest -q tests/test_layers.py tests/test_searcher.py

* refactor: reuse a default backend instance in palace helper

Tighten the stage-1 backend seam by promoting the default Chroma backend
adapter to a module-level singleton in `mempalace/palace.py`.

This keeps the stage-1 scope unchanged — Chroma is still the only backend
wired in this branch — but avoids constructing a fresh `ChromaBackend()`
object on every `get_collection()` call. The backend is stateless today,
so this is a readability/cleanup change rather than a behavioral one.

Why this helps:
- makes `palace.get_collection()` read like a real default factory instead
  of an inline constructor call
- keeps the stage-1 branch a little cleaner before opening the public PR
- does not widen the backend surface or change any config/runtime behavior

Verification:
- python3 -m py_compile mempalace/palace.py
- pytest -q tests/test_miner.py tests/test_layers.py tests/test_searcher.py
- pytest -q  # 529 passed, 106 deselected

* fix: harden read-only seam behavior and update seam tests

Preserve the stage-1 backend abstraction while closing the real read-path
regression surfaced in PR review.

What changed:
- make ChromaBackend.get_collection(create=False) fail fast when the palace
  directory does not exist instead of letting PersistentClient create it as a
  side effect
- update miner.status() to call get_collection(..., create=False) so status
  keeps the historical 'No palace found' behavior
- remove the temporary chromadb shim aliases from layers.py and searcher.py
  now that the tests patch the seam directly
- add focused tests for the new backends package, including ChromaCollection
  delegation and ChromaBackend create=True/create=False behavior
- retarget layer/searcher tests to patch the backend seam instead of patching
  chromadb.PersistentClient inside production modules
- add a regression test that status() does not create an empty palace when the
  target path is missing

Verification:
- ruff check .
- uv run pytest -q
- uv run pytest -q tests/test_backends.py tests/test_cli.py tests/test_mcp_server.py tests/test_layers.py tests/test_searcher.py tests/test_miner.py

Notes:
- the separate benchmark/slow/stress layer was started as a soak but not used
  as the merge gate for this PR branch

* refactor: drop duplicate mcp collection cache declaration

Remove a redundant `_collection_cache = None` assignment in
`mempalace/mcp_server.py` left over after the stage-1 backend seam refactor.

This does not change behavior; it only trims review noise in the MCP server
module after the read-path hardening pass.

Verification:
- ruff check mempalace/mcp_server.py
- uv run pytest -q tests/test_mcp_server.py

---------

Co-authored-by: Sergey Kuznetsov <sergey@iterudit.com>

mempalace/backends/__init__.py

@@ -0,0 +1,6 @@
+"""Storage backend implementations for MemPalace."""
+
+from .base import BaseCollection
+from .chroma import ChromaBackend, ChromaCollection
+
+__all__ = ["BaseCollection", "ChromaBackend", "ChromaCollection"]

mempalace/backends/base.py

@@ -0,0 +1,44 @@
+"""Abstract collection interface for MemPalace storage backends."""
+
+from abc import ABC, abstractmethod
+from typing import Any, Dict, List, Optional
+
+
+class BaseCollection(ABC):
+    """Smallest collection contract the rest of MemPalace relies on."""
+
+    @abstractmethod
+    def add(
+        self,
+        *,
+        documents: List[str],
+        ids: List[str],
+        metadatas: Optional[List[Dict[str, Any]]] = None,
+    ) -> None:
+        raise NotImplementedError
+
+    @abstractmethod
+    def upsert(
+        self,
+        *,
+        documents: List[str],
+        ids: List[str],
+        metadatas: Optional[List[Dict[str, Any]]] = None,
+    ) -> None:
+        raise NotImplementedError
+
+    @abstractmethod
+    def query(self, **kwargs: Any) -> Dict[str, Any]:
+        raise NotImplementedError
+
+    @abstractmethod
+    def get(self, **kwargs: Any) -> Dict[str, Any]:
+        raise NotImplementedError
+
+    @abstractmethod
+    def delete(self, **kwargs: Any) -> None:
+        raise NotImplementedError
+
+    @abstractmethod
+    def count(self) -> int:
+        raise NotImplementedError

mempalace/backends/chroma.py

@@ -0,0 +1,54 @@
+"""ChromaDB-backed MemPalace collection adapter."""
+
+import os
+
+import chromadb
+
+from .base import BaseCollection
+
+
+class ChromaCollection(BaseCollection):
+    """Thin adapter over a ChromaDB collection."""
+
+    def __init__(self, collection):
+        self._collection = collection
+
+    def add(self, *, documents, ids, metadatas=None):
+        self._collection.add(documents=documents, ids=ids, metadatas=metadatas)
+
+    def upsert(self, *, documents, ids, metadatas=None):
+        self._collection.upsert(documents=documents, ids=ids, metadatas=metadatas)
+
+    def query(self, **kwargs):
+        return self._collection.query(**kwargs)
+
+    def get(self, **kwargs):
+        return self._collection.get(**kwargs)
+
+    def delete(self, **kwargs):
+        self._collection.delete(**kwargs)
+
+    def count(self):
+        return self._collection.count()
+
+
+class ChromaBackend:
+    """Factory for MemPalace's default ChromaDB backend."""
+
+    def get_collection(self, palace_path: str, collection_name: str, create: bool = False):
+        if not create and not os.path.isdir(palace_path):
+            raise FileNotFoundError(palace_path)
+
+        if create:
+            os.makedirs(palace_path, exist_ok=True)
+            try:
+                os.chmod(palace_path, 0o700)
+            except (OSError, NotImplementedError):
+                pass
+
+        client = chromadb.PersistentClient(path=palace_path)
+        if create:
+            collection = client.get_or_create_collection(collection_name)
+        else:
+            collection = client.get_collection(collection_name)
+        return ChromaCollection(collection)

mempalace/layers.py

@@ -21,9 +21,8 @@ import sys
 from pathlib import Path
 from collections import defaultdict
 
-import chromadb
-
 from .config import MempalaceConfig
+from .palace import get_collection as _get_collection
 
 
 # ---------------------------------------------------------------------------
@@ -91,8 +90,7 @@ class Layer1:
     def generate(self) -> str:
         """Pull top drawers from ChromaDB and format as compact L1 text."""
         try:
-            client = chromadb.PersistentClient(path=self.palace_path)
-            col = client.get_collection("mempalace_drawers")
+            col = _get_collection(self.palace_path, create=False)
         except Exception:
             return "## L1 — No palace found. Run: mempalace mine <dir>"
 
@@ -196,8 +194,7 @@ class Layer2:
     def retrieve(self, wing: str = None, room: str = None, n_results: int = 10) -> str:
         """Retrieve drawers filtered by wing and/or room."""
         try:
-            client = chromadb.PersistentClient(path=self.palace_path)
-            col = client.get_collection("mempalace_drawers")
+            col = _get_collection(self.palace_path, create=False)
         except Exception:
             return "No palace found."
 
@@ -260,8 +257,7 @@ class Layer3:
     def search(self, query: str, wing: str = None, room: str = None, n_results: int = 5) -> str:
         """Semantic search, returns compact result text."""
         try:
-            client = chromadb.PersistentClient(path=self.palace_path)
-            col = client.get_collection("mempalace_drawers")
+            col = _get_collection(self.palace_path, create=False)
         except Exception:
             return "No palace found."
 
@@ -316,8 +312,7 @@ class Layer3:
     ) -> list:
         """Return raw dicts instead of formatted text."""
         try:
-            client = chromadb.PersistentClient(path=self.palace_path)
-            col = client.get_collection("mempalace_drawers")
+            col = _get_collection(self.palace_path, create=False)
         except Exception:
             return []
 
@@ -437,8 +432,7 @@ class MemoryStack:
 
         # Count drawers
         try:
-            client = chromadb.PersistentClient(path=self.palace_path)
-            col = client.get_collection("mempalace_drawers")
+            col = _get_collection(self.palace_path, create=False)
             count = col.count()
             result["total_drawers"] = count
         except Exception:

mempalace/mcp_server.py

@@ -28,10 +28,10 @@ from pathlib import Path
 
 from .config import MempalaceConfig, sanitize_name, sanitize_content
 from .version import __version__
+from .palace import get_collection as _get_collection_from_palace
 from .query_sanitizer import sanitize_query
 from .searcher import search_memories
 from .palace_graph import traverse, find_tunnels, graph_stats
-import chromadb
 
 from .knowledge_graph import KnowledgeGraph
 
@@ -64,7 +64,6 @@ else:
     _kg = KnowledgeGraph()
 
 
-_client_cache = None
 _collection_cache = None
 
 
@@ -101,27 +100,16 @@ def _wal_log(operation: str, params: dict, result: dict = None):
         logger.error(f"WAL write failed: {e}")
 
 
-_client_cache = None
-_collection_cache = None
-
-
-def _get_client():
-    """Return a singleton ChromaDB PersistentClient."""
-    global _client_cache
-    if _client_cache is None:
-        _client_cache = chromadb.PersistentClient(path=_config.palace_path)
-    return _client_cache
-
-
 def _get_collection(create=False):
-    """Return the ChromaDB collection, caching the client between calls."""
+    """Return the configured collection, caching the wrapper between calls."""
     global _collection_cache
     try:
-        client = _get_client()
-        if create:
-            _collection_cache = client.get_or_create_collection(_config.collection_name)
-        elif _collection_cache is None:
-            _collection_cache = client.get_collection(_config.collection_name)
+        if create or _collection_cache is None:
+            _collection_cache = _get_collection_from_palace(
+                _config.palace_path,
+                collection_name=_config.collection_name,
+                create=create,
+            )
         return _collection_cache
     except Exception:
         return None

mempalace/miner.py

@@ -15,8 +15,6 @@ from pathlib import Path
 from datetime import datetime
 from collections import defaultdict
 
-import chromadb
-
 from .palace import SKIP_DIRS, get_collection, file_already_mined
 
 READABLE_EXTENSIONS = {
@@ -625,8 +623,7 @@ def mine(
 def status(palace_path: str):
     """Show what's been filed in the palace."""
     try:
-        client = chromadb.PersistentClient(path=palace_path)
-        col = client.get_collection("mempalace_drawers")
+        col = get_collection(palace_path, create=False)
     except Exception:
         print(f"\n  No palace found at {palace_path}")
         print("  Run: mempalace init <dir> then mempalace mine <dir>")

mempalace/palace.py

@@ -1,11 +1,12 @@
 """
 palace.py — Shared palace operations.
 
-Consolidates ChromaDB access patterns used by both miners and the MCP server.
+Consolidates collection access patterns used by both miners and the MCP server.
 """
 
 import os
-import chromadb
+
+from .backends.chroma import ChromaBackend
 
 SKIP_DIRS = {
     ".git",
@@ -33,19 +34,20 @@ SKIP_DIRS = {
     "target",
 }
 
+_DEFAULT_BACKEND = ChromaBackend()
 
-def get_collection(palace_path: str, collection_name: str = "mempalace_drawers"):
-    """Get or create the palace ChromaDB collection."""
-    os.makedirs(palace_path, exist_ok=True)
-    try:
-        os.chmod(palace_path, 0o700)
-    except (OSError, NotImplementedError):
-        pass
-    client = chromadb.PersistentClient(path=palace_path)
-    try:
-        return client.get_collection(collection_name)
-    except Exception:
-        return client.create_collection(collection_name)
+
+def get_collection(
+    palace_path: str,
+    collection_name: str = "mempalace_drawers",
+    create: bool = True,
+):
+    """Get the palace collection through the backend layer."""
+    return _DEFAULT_BACKEND.get_collection(
+        palace_path,
+        collection_name=collection_name,
+        create=create,
+    )
 
 
 def file_already_mined(collection, source_file: str, check_mtime: bool = False) -> bool:

mempalace/palace_graph.py

@@ -16,16 +16,19 @@ No external graph DB needed — built from ChromaDB metadata.
 """
 
 from collections import defaultdict, Counter
-from .config import MempalaceConfig
 
-import chromadb
+from .config import MempalaceConfig
+from .palace import get_collection as _get_palace_collection
 
 
 def _get_collection(config=None):
     config = config or MempalaceConfig()
     try:
-        client = chromadb.PersistentClient(path=config.palace_path)
-        return client.get_collection(config.collection_name)
+        return _get_palace_collection(
+            config.palace_path,
+            collection_name=config.collection_name,
+            create=False,
+        )
     except Exception:
         return None
 

mempalace/searcher.py

@@ -9,7 +9,7 @@ Returns verbatim text — the actual words, never summaries.
 import logging
 from pathlib import Path
 
-import chromadb
+from .palace import get_collection
 
 logger = logging.getLogger("mempalace_mcp")
 
@@ -24,8 +24,7 @@ def search(query: str, palace_path: str, wing: str = None, room: str = None, n_r
     Optionally filter by wing (project) or room (aspect).
     """
     try:
-        client = chromadb.PersistentClient(path=palace_path)
-        col = client.get_collection("mempalace_drawers")
+        col = get_collection(palace_path, create=False)
     except Exception:
         print(f"\n  No palace found at {palace_path}")
         print("  Run: mempalace init <dir> then mempalace mine <dir>")
@@ -98,8 +97,7 @@ def search_memories(
     Used by the MCP server and other callers that need data.
     """
     try:
-        client = chromadb.PersistentClient(path=palace_path)
-        col = client.get_collection("mempalace_drawers")
+        col = get_collection(palace_path, create=False)
     except Exception as e:
         logger.error("No palace found at %s: %s", palace_path, e)
         return {

tests/test_backends.py

@@ -0,0 +1,80 @@
+import chromadb
+import pytest
+
+from mempalace.backends.chroma import ChromaBackend, ChromaCollection
+
+
+class _FakeCollection:
+    def __init__(self):
+        self.calls = []
+
+    def add(self, **kwargs):
+        self.calls.append(("add", kwargs))
+
+    def upsert(self, **kwargs):
+        self.calls.append(("upsert", kwargs))
+
+    def query(self, **kwargs):
+        self.calls.append(("query", kwargs))
+        return {"kind": "query"}
+
+    def get(self, **kwargs):
+        self.calls.append(("get", kwargs))
+        return {"kind": "get"}
+
+    def delete(self, **kwargs):
+        self.calls.append(("delete", kwargs))
+
+    def count(self):
+        self.calls.append(("count", {}))
+        return 7
+
+
+def test_chroma_collection_delegates_methods():
+    fake = _FakeCollection()
+    collection = ChromaCollection(fake)
+
+    collection.add(documents=["d"], ids=["1"], metadatas=[{"wing": "w"}])
+    collection.upsert(documents=["u"], ids=["2"], metadatas=[{"room": "r"}])
+    assert collection.query(query_texts=["q"]) == {"kind": "query"}
+    assert collection.get(where={"wing": "w"}) == {"kind": "get"}
+    collection.delete(ids=["1"])
+    assert collection.count() == 7
+
+    assert fake.calls == [
+        ("add", {"documents": ["d"], "ids": ["1"], "metadatas": [{"wing": "w"}]}),
+        ("upsert", {"documents": ["u"], "ids": ["2"], "metadatas": [{"room": "r"}]}),
+        ("query", {"query_texts": ["q"]}),
+        ("get", {"where": {"wing": "w"}}),
+        ("delete", {"ids": ["1"]}),
+        ("count", {}),
+    ]
+
+
+def test_chroma_backend_create_false_raises_without_creating_directory(tmp_path):
+    palace_path = tmp_path / "missing-palace"
+
+    with pytest.raises(FileNotFoundError):
+        ChromaBackend().get_collection(
+            str(palace_path),
+            collection_name="mempalace_drawers",
+            create=False,
+        )
+
+    assert not palace_path.exists()
+
+
+def test_chroma_backend_create_true_creates_directory_and_collection(tmp_path):
+    palace_path = tmp_path / "palace"
+
+    collection = ChromaBackend().get_collection(
+        str(palace_path),
+        collection_name="mempalace_drawers",
+        create=True,
+    )
+
+    assert palace_path.is_dir()
+    assert isinstance(collection, ChromaCollection)
+
+    client = chromadb.PersistentClient(path=str(palace_path))
+    client.get_collection("mempalace_drawers")

tests/test_layers.py

@@ -71,16 +71,14 @@ def test_layer0_default_path():
 
 
 def _mock_chromadb_for_layer(docs, metas, monkeypatch=None):
-    """Return a mock PersistentClient whose collection.get returns docs/metas."""
+    """Return a mock collection whose get() returns docs/metas."""
     mock_col = MagicMock()
     # First batch returns data, second batch returns empty (end of pagination)
     mock_col.get.side_effect = [
         {"documents": docs, "metadatas": metas},
         {"documents": [], "metadatas": []},
     ]
-    mock_client = MagicMock()
-    mock_client.get_collection.return_value = mock_col
-    return mock_client
+    return mock_col
 
 
 def test_layer1_no_palace():
@@ -101,11 +99,11 @@ def test_layer1_generates_essential_story():
         {"room": "decisions", "source_file": "meeting.txt", "importance": 5},
         {"room": "architecture", "source_file": "design.txt", "importance": 4},
     ]
-    mock_client = _mock_chromadb_for_layer(docs, metas)
+    mock_col = _mock_chromadb_for_layer(docs, metas)
 
     with (
         patch("mempalace.layers.MempalaceConfig") as mock_cfg,
-        patch("mempalace.layers.chromadb.PersistentClient", return_value=mock_client),
+        patch("mempalace.layers._get_collection", return_value=mock_col),
     ):
         mock_cfg.return_value.palace_path = "/fake"
         layer = Layer1(palace_path="/fake")
@@ -118,12 +116,9 @@ def test_layer1_generates_essential_story():
 def test_layer1_empty_palace():
     mock_col = MagicMock()
     mock_col.get.return_value = {"documents": [], "metadatas": []}
-    mock_client = MagicMock()
-    mock_client.get_collection.return_value = mock_col
-
     with (
         patch("mempalace.layers.MempalaceConfig") as mock_cfg,
-        patch("mempalace.layers.chromadb.PersistentClient", return_value=mock_client),
+        patch("mempalace.layers._get_collection", return_value=mock_col),
     ):
         mock_cfg.return_value.palace_path = "/fake"
         layer = Layer1(palace_path="/fake")
@@ -135,11 +130,11 @@ def test_layer1_empty_palace():
 def test_layer1_with_wing_filter():
     docs = ["Memory about project X"]
     metas = [{"room": "general", "source_file": "x.txt", "importance": 3}]
-    mock_client = _mock_chromadb_for_layer(docs, metas)
+    mock_col = _mock_chromadb_for_layer(docs, metas)
 
     with (
         patch("mempalace.layers.MempalaceConfig") as mock_cfg,
-        patch("mempalace.layers.chromadb.PersistentClient", return_value=mock_client),
+        patch("mempalace.layers._get_collection", return_value=mock_col),
     ):
         mock_cfg.return_value.palace_path = "/fake"
         layer = Layer1(palace_path="/fake", wing="project_x")
@@ -147,18 +142,18 @@ def test_layer1_with_wing_filter():
 
     assert "ESSENTIAL STORY" in result
     # Verify wing filter was passed
-    call_kwargs = mock_client.get_collection.return_value.get.call_args_list[0][1]
+    call_kwargs = mock_col.get.call_args_list[0][1]
     assert call_kwargs.get("where") == {"wing": "project_x"}
 
 
 def test_layer1_truncates_long_snippets():
     docs = ["A" * 300]
     metas = [{"room": "general", "source_file": "long.txt"}]
-    mock_client = _mock_chromadb_for_layer(docs, metas)
+    mock_col = _mock_chromadb_for_layer(docs, metas)
 
     with (
         patch("mempalace.layers.MempalaceConfig") as mock_cfg,
-        patch("mempalace.layers.chromadb.PersistentClient", return_value=mock_client),
+        patch("mempalace.layers._get_collection", return_value=mock_col),
     ):
         mock_cfg.return_value.palace_path = "/fake"
         layer = Layer1(palace_path="/fake")
@@ -171,11 +166,11 @@ def test_layer1_respects_max_chars():
     """L1 stops adding entries once MAX_CHARS is reached."""
     docs = [f"Memory number {i} with substantial content padding here" for i in range(30)]
     metas = [{"room": "general", "source_file": f"f{i}.txt", "importance": 5} for i in range(30)]
-    mock_client = _mock_chromadb_for_layer(docs, metas)
+    mock_col = _mock_chromadb_for_layer(docs, metas)
 
     with (
         patch("mempalace.layers.MempalaceConfig") as mock_cfg,
-        patch("mempalace.layers.chromadb.PersistentClient", return_value=mock_client),
+        patch("mempalace.layers._get_collection", return_value=mock_col),
     ):
         mock_cfg.return_value.palace_path = "/fake"
         layer = Layer1(palace_path="/fake")
@@ -193,11 +188,11 @@ def test_layer1_importance_from_various_keys():
         {"room": "r", "weight": 1},
         {"room": "r"},  # no weight key, defaults to 3
     ]
-    mock_client = _mock_chromadb_for_layer(docs, metas)
+    mock_col = _mock_chromadb_for_layer(docs, metas)
 
     with (
         patch("mempalace.layers.MempalaceConfig") as mock_cfg,
-        patch("mempalace.layers.chromadb.PersistentClient", return_value=mock_client),
+        patch("mempalace.layers._get_collection", return_value=mock_col),
     ):
         mock_cfg.return_value.palace_path = "/fake"
         layer = Layer1(palace_path="/fake")
@@ -213,12 +208,9 @@ def test_layer1_batch_exception_breaks():
         {"documents": ["doc1"], "metadatas": [{"room": "r"}]},
         RuntimeError("batch error"),
     ]
-    mock_client = MagicMock()
-    mock_client.get_collection.return_value = mock_col
-
     with (
         patch("mempalace.layers.MempalaceConfig") as mock_cfg,
-        patch("mempalace.layers.chromadb.PersistentClient", return_value=mock_client),
+        patch("mempalace.layers._get_collection", return_value=mock_col),
     ):
         mock_cfg.return_value.palace_path = "/fake"
         layer = Layer1(palace_path="/fake")
@@ -244,12 +236,9 @@ def test_layer2_retrieve_with_wing():
         "documents": ["Some memory about the project"],
         "metadatas": [{"room": "backend", "source_file": "notes.txt"}],
     }
-    mock_client = MagicMock()
-    mock_client.get_collection.return_value = mock_col
-
     with (
         patch("mempalace.layers.MempalaceConfig") as mock_cfg,
-        patch("mempalace.layers.chromadb.PersistentClient", return_value=mock_client),
+        patch("mempalace.layers._get_collection", return_value=mock_col),
     ):
         mock_cfg.return_value.palace_path = "/fake"
         layer = Layer2(palace_path="/fake")
@@ -265,12 +254,9 @@ def test_layer2_retrieve_with_room():
         "documents": ["Backend architecture notes"],
         "metadatas": [{"room": "architecture", "source_file": "arch.txt"}],
     }
-    mock_client = MagicMock()
-    mock_client.get_collection.return_value = mock_col
-
     with (
         patch("mempalace.layers.MempalaceConfig") as mock_cfg,
-        patch("mempalace.layers.chromadb.PersistentClient", return_value=mock_client),
+        patch("mempalace.layers._get_collection", return_value=mock_col),
     ):
         mock_cfg.return_value.palace_path = "/fake"
         layer = Layer2(palace_path="/fake")
@@ -285,12 +271,9 @@ def test_layer2_retrieve_wing_and_room():
         "documents": ["Filtered result"],
         "metadatas": [{"room": "backend", "source_file": "x.txt"}],
     }
-    mock_client = MagicMock()
-    mock_client.get_collection.return_value = mock_col
-
     with (
         patch("mempalace.layers.MempalaceConfig") as mock_cfg,
-        patch("mempalace.layers.chromadb.PersistentClient", return_value=mock_client),
+        patch("mempalace.layers._get_collection", return_value=mock_col),
     ):
         mock_cfg.return_value.palace_path = "/fake"
         layer = Layer2(palace_path="/fake")
@@ -304,12 +287,9 @@ def test_layer2_retrieve_wing_and_room():
 def test_layer2_retrieve_empty():
     mock_col = MagicMock()
     mock_col.get.return_value = {"documents": [], "metadatas": []}
-    mock_client = MagicMock()
-    mock_client.get_collection.return_value = mock_col
-
     with (
         patch("mempalace.layers.MempalaceConfig") as mock_cfg,
-        patch("mempalace.layers.chromadb.PersistentClient", return_value=mock_client),
+        patch("mempalace.layers._get_collection", return_value=mock_col),
     ):
         mock_cfg.return_value.palace_path = "/fake"
         layer = Layer2(palace_path="/fake")
@@ -321,12 +301,9 @@ def test_layer2_retrieve_empty():
 def test_layer2_retrieve_no_filter():
     mock_col = MagicMock()
     mock_col.get.return_value = {"documents": [], "metadatas": []}
-    mock_client = MagicMock()
-    mock_client.get_collection.return_value = mock_col
-
     with (
         patch("mempalace.layers.MempalaceConfig") as mock_cfg,
-        patch("mempalace.layers.chromadb.PersistentClient", return_value=mock_client),
+        patch("mempalace.layers._get_collection", return_value=mock_col),
     ):
         mock_cfg.return_value.palace_path = "/fake"
         layer = Layer2(palace_path="/fake")
@@ -340,12 +317,9 @@ def test_layer2_retrieve_no_filter():
 def test_layer2_retrieve_error():
     mock_col = MagicMock()
     mock_col.get.side_effect = RuntimeError("db error")
-    mock_client = MagicMock()
-    mock_client.get_collection.return_value = mock_col
-
     with (
         patch("mempalace.layers.MempalaceConfig") as mock_cfg,
-        patch("mempalace.layers.chromadb.PersistentClient", return_value=mock_client),
+        patch("mempalace.layers._get_collection", return_value=mock_col),
     ):
         mock_cfg.return_value.palace_path = "/fake"
         layer = Layer2(palace_path="/fake")
@@ -360,12 +334,9 @@ def test_layer2_truncates_long_snippets():
         "documents": ["B" * 400],
         "metadatas": [{"room": "r", "source_file": "s.txt"}],
     }
-    mock_client = MagicMock()
-    mock_client.get_collection.return_value = mock_col
-
     with (
         patch("mempalace.layers.MempalaceConfig") as mock_cfg,
-        patch("mempalace.layers.chromadb.PersistentClient", return_value=mock_client),
+        patch("mempalace.layers._get_collection", return_value=mock_col),
     ):
         mock_cfg.return_value.palace_path = "/fake"
         layer = Layer2(palace_path="/fake")
@@ -408,12 +379,9 @@ def test_layer3_search_with_results():
         [{"wing": "project", "room": "backend", "source_file": "notes.txt"}],
         [0.2],
     )
-    mock_client = MagicMock()
-    mock_client.get_collection.return_value = mock_col
-
     with (
         patch("mempalace.layers.MempalaceConfig") as mock_cfg,
-        patch("mempalace.layers.chromadb.PersistentClient", return_value=mock_client),
+        patch("mempalace.layers._get_collection", return_value=mock_col),
     ):
         mock_cfg.return_value.palace_path = "/fake"
         layer = Layer3(palace_path="/fake")
@@ -427,12 +395,9 @@ def test_layer3_search_with_results():
 def test_layer3_search_no_results():
     mock_col = MagicMock()
     mock_col.query.return_value = _mock_query_results([], [], [])
-    mock_client = MagicMock()
-    mock_client.get_collection.return_value = mock_col
-
     with (
         patch("mempalace.layers.MempalaceConfig") as mock_cfg,
-        patch("mempalace.layers.chromadb.PersistentClient", return_value=mock_client),
+        patch("mempalace.layers._get_collection", return_value=mock_col),
     ):
         mock_cfg.return_value.palace_path = "/fake"
         layer = Layer3(palace_path="/fake")
@@ -448,12 +413,9 @@ def test_layer3_search_with_wing_filter():
         [{"wing": "proj", "room": "r"}],
         [0.1],
     )
-    mock_client = MagicMock()
-    mock_client.get_collection.return_value = mock_col
-
     with (
         patch("mempalace.layers.MempalaceConfig") as mock_cfg,
-        patch("mempalace.layers.chromadb.PersistentClient", return_value=mock_client),
+        patch("mempalace.layers._get_collection", return_value=mock_col),
     ):
         mock_cfg.return_value.palace_path = "/fake"
         layer = Layer3(palace_path="/fake")
@@ -470,12 +432,9 @@ def test_layer3_search_with_room_filter():
         [{"wing": "w", "room": "backend"}],
         [0.1],
     )
-    mock_client = MagicMock()
-    mock_client.get_collection.return_value = mock_col
-
     with (
         patch("mempalace.layers.MempalaceConfig") as mock_cfg,
-        patch("mempalace.layers.chromadb.PersistentClient", return_value=mock_client),
+        patch("mempalace.layers._get_collection", return_value=mock_col),
     ):
         mock_cfg.return_value.palace_path = "/fake"
         layer = Layer3(palace_path="/fake")
@@ -492,12 +451,9 @@ def test_layer3_search_with_wing_and_room():
         [{"wing": "proj", "room": "backend"}],
         [0.1],
     )
-    mock_client = MagicMock()
-    mock_client.get_collection.return_value = mock_col
-
     with (
         patch("mempalace.layers.MempalaceConfig") as mock_cfg,
-        patch("mempalace.layers.chromadb.PersistentClient", return_value=mock_client),
+        patch("mempalace.layers._get_collection", return_value=mock_col),
     ):
         mock_cfg.return_value.palace_path = "/fake"
         layer = Layer3(palace_path="/fake")
@@ -510,12 +466,9 @@ def test_layer3_search_with_wing_and_room():
 def test_layer3_search_error():
     mock_col = MagicMock()
     mock_col.query.side_effect = RuntimeError("search failed")
-    mock_client = MagicMock()
-    mock_client.get_collection.return_value = mock_col
-
     with (
         patch("mempalace.layers.MempalaceConfig") as mock_cfg,
-        patch("mempalace.layers.chromadb.PersistentClient", return_value=mock_client),
+        patch("mempalace.layers._get_collection", return_value=mock_col),
     ):
         mock_cfg.return_value.palace_path = "/fake"
         layer = Layer3(palace_path="/fake")
@@ -531,12 +484,9 @@ def test_layer3_search_truncates_long_docs():
         [{"wing": "w", "room": "r", "source_file": "s.txt"}],
         [0.1],
     )
-    mock_client = MagicMock()
-    mock_client.get_collection.return_value = mock_col
-
     with (
         patch("mempalace.layers.MempalaceConfig") as mock_cfg,
-        patch("mempalace.layers.chromadb.PersistentClient", return_value=mock_client),
+        patch("mempalace.layers._get_collection", return_value=mock_col),
     ):
         mock_cfg.return_value.palace_path = "/fake"
         layer = Layer3(palace_path="/fake")
@@ -552,12 +502,9 @@ def test_layer3_search_raw_returns_dicts():
         [{"wing": "proj", "room": "backend", "source_file": "f.txt"}],
         [0.3],
     )
-    mock_client = MagicMock()
-    mock_client.get_collection.return_value = mock_col
-
     with (
         patch("mempalace.layers.MempalaceConfig") as mock_cfg,
-        patch("mempalace.layers.chromadb.PersistentClient", return_value=mock_client),
+        patch("mempalace.layers._get_collection", return_value=mock_col),
     ):
         mock_cfg.return_value.palace_path = "/fake"
         layer = Layer3(palace_path="/fake")
@@ -577,12 +524,9 @@ def test_layer3_search_raw_with_filters():
         [{"wing": "w", "room": "r"}],
         [0.1],
     )
-    mock_client = MagicMock()
-    mock_client.get_collection.return_value = mock_col
-
     with (
         patch("mempalace.layers.MempalaceConfig") as mock_cfg,
-        patch("mempalace.layers.chromadb.PersistentClient", return_value=mock_client),
+        patch("mempalace.layers._get_collection", return_value=mock_col),
     ):
         mock_cfg.return_value.palace_path = "/fake"
         layer = Layer3(palace_path="/fake")
@@ -595,12 +539,9 @@ def test_layer3_search_raw_with_filters():
 def test_layer3_search_raw_error():
     mock_col = MagicMock()
     mock_col.query.side_effect = RuntimeError("fail")
-    mock_client = MagicMock()
-    mock_client.get_collection.return_value = mock_col
-
     with (
         patch("mempalace.layers.MempalaceConfig") as mock_cfg,
-        patch("mempalace.layers.chromadb.PersistentClient", return_value=mock_client),
+        patch("mempalace.layers._get_collection", return_value=mock_col),
     ):
         mock_cfg.return_value.palace_path = "/fake"
         layer = Layer3(palace_path="/fake")
@@ -701,12 +642,9 @@ def test_memory_stack_status_with_palace(tmp_path):
 
     mock_col = MagicMock()
     mock_col.count.return_value = 42
-    mock_client = MagicMock()
-    mock_client.get_collection.return_value = mock_col
-
     with (
         patch("mempalace.layers.MempalaceConfig") as mock_cfg,
-        patch("mempalace.layers.chromadb.PersistentClient", return_value=mock_client),
+        patch("mempalace.layers._get_collection", return_value=mock_col),
     ):
         mock_cfg.return_value.palace_path = "/fake"
         stack = MemoryStack(

tests/test_miner.py

@@ -6,7 +6,7 @@ from pathlib import Path
 import chromadb
 import yaml
 
-from mempalace.miner import mine, scan_project
+from mempalace.miner import mine, scan_project, status
 from mempalace.palace import file_already_mined
 
 
@@ -260,3 +260,13 @@ def test_file_already_mined_check_mtime():
         # Release ChromaDB file handles before cleanup (required on Windows)
         del col, client
         shutil.rmtree(tmpdir, ignore_errors=True)
+
+
+def test_status_missing_palace_does_not_create_empty_collection(tmp_path, capsys):
+    palace_path = tmp_path / "missing-palace"
+
+    status(str(palace_path))
+
+    out = capsys.readouterr().out
+    assert "No palace found" in out
+    assert not palace_path.exists()

tests/test_searcher.py

@@ -56,10 +56,8 @@ class TestSearchMemories:
         """search_memories returns error dict when query raises."""
         mock_col = MagicMock()
         mock_col.query.side_effect = RuntimeError("query failed")
-        mock_client = MagicMock()
-        mock_client.get_collection.return_value = mock_col
 
-        with patch("mempalace.searcher.chromadb.PersistentClient", return_value=mock_client):
+        with patch("mempalace.searcher.get_collection", return_value=mock_col):
             result = search_memories("test", "/fake/path")
         assert "error" in result
         assert "query failed" in result["error"]
@@ -111,10 +109,8 @@ class TestSearchCLI:
         """search raises SearchError when query fails."""
         mock_col = MagicMock()
         mock_col.query.side_effect = RuntimeError("boom")
-        mock_client = MagicMock()
-        mock_client.get_collection.return_value = mock_col
 
-        with patch("mempalace.searcher.chromadb.PersistentClient", return_value=mock_client):
+        with patch("mempalace.searcher.get_collection", return_value=mock_col):
             with pytest.raises(SearchError, match="Search error"):
                 search("test", "/fake/path")