fix(vector_stores): use platform user-data dir instead of /tmp/{provider}

The default vector store path was /tmp/{provider}, which breaks in a few
real deployments:

- macOS LaunchAgents (sandbox often blocks /tmp writes; /tmp is periodically cleaned)
- systemd services with PrivateTmp= or noexec /tmp
- Windows (no /tmp at all)
- Docker (/tmp is ephemeral unless mounted)

Resolution order is now:
  1. MEM0_DATA_DIR env var (explicit override)
  2. Platform convention via stdlib:
     - macOS: ~/Library/Application Support/mem0
     - Windows: %LOCALAPPDATA%/mem0
     - Linux/BSD: $XDG_DATA_HOME/mem0 or ~/.local/share/mem0
  3. provider name appended as the subdir

Explicit path in user config still wins over both the env var and the
default, so behavior for anyone already setting path= is unchanged.

Refs #4279

Author: alvinttang

mem0/vector_stores/configs.py

@@ -1,8 +1,40 @@
+import os
+import sys
 from typing import Dict, Optional
 
 from pydantic import BaseModel, Field, model_validator
 
 
+def _default_data_dir() -> str:
+    """Return a writable user-data directory suitable for embedded vector stores.
+
+    Resolution order:
+      1. ``MEM0_DATA_DIR`` environment variable (explicit override).
+      2. Platform convention:
+         - macOS: ``~/Library/Application Support/mem0``
+         - Windows: ``%LOCALAPPDATA%/mem0``
+         - Linux/BSD: ``$XDG_DATA_HOME/mem0`` or ``~/.local/share/mem0``
+
+    The previous default of ``/tmp/{provider}`` broke macOS LaunchAgents, systemd
+    services with ``noexec`` ``/tmp``, Windows (no ``/tmp``), and Docker (ephemeral
+    ``/tmp``). See #4279.
+    """
+    env_dir = os.environ.get("MEM0_DATA_DIR")
+    if env_dir:
+        return env_dir
+    if sys.platform == "darwin":
+        return os.path.expanduser("~/Library/Application Support/mem0")
+    if sys.platform == "win32":
+        return os.path.join(
+            os.environ.get("LOCALAPPDATA") or os.path.expanduser("~/AppData/Local"),
+            "mem0",
+        )
+    return os.path.join(
+        os.environ.get("XDG_DATA_HOME") or os.path.expanduser("~/.local/share"),
+        "mem0",
+    )
+
+
 class VectorStoreConfig(BaseModel):
     provider: str = Field(
         description="Provider of the vector store (e.g., 'qdrant', 'chroma', 'upstash_vector')",
@@ -61,7 +93,7 @@ def validate_and_create_config(self) -> "VectorStoreConfig":
 
         # also check if path in allowed kays for pydantic model, and whether config extra fields are allowed
         if "path" not in config and "path" in config_class.__annotations__:
-            config["path"] = f"/tmp/{provider}"
+            config["path"] = os.path.join(_default_data_dir(), provider)
 
         self.config = config_class(**config)
         return self

tests/vector_stores/test_default_path.py

@@ -0,0 +1,49 @@
+"""Regression test for #4279: vector store path defaults to /tmp/{provider}, which
+fails or silently loses data in macOS LaunchAgents, systemd services, Docker, etc.
+"""
+import os
+import sys
+from unittest.mock import patch
+
+import pytest
+
+from mem0.vector_stores.configs import VectorStoreConfig
+
+
+def test_default_path_is_not_tmp():
+    """The default path must not be /tmp/{provider} on any platform."""
+    cfg = VectorStoreConfig(provider="faiss", config={})
+    path = cfg.config.path
+    assert path is not None
+    assert not path.startswith("/tmp/"), f"default path still falls back to /tmp: {path}"
+    assert path.endswith("faiss")
+
+
+def test_env_var_override():
+    """MEM0_DATA_DIR must override the platform default."""
+    with patch.dict(os.environ, {"MEM0_DATA_DIR": "/var/lib/mem0_test"}):
+        cfg = VectorStoreConfig(provider="faiss", config={})
+        assert cfg.config.path == os.path.join("/var/lib/mem0_test", "faiss")
+
+
+def test_explicit_path_wins():
+    """An explicit path in the user config must beat both the env var and the default."""
+    with patch.dict(os.environ, {"MEM0_DATA_DIR": "/should/not/leak"}):
+        cfg = VectorStoreConfig(provider="faiss", config={"path": "/explicit/user/path"})
+        assert cfg.config.path == "/explicit/user/path"
+
+
+@pytest.mark.skipif(sys.platform != "darwin", reason="macOS-specific default")
+def test_macos_default_uses_application_support():
+    with patch.dict(os.environ, {}, clear=False):
+        os.environ.pop("MEM0_DATA_DIR", None)
+        cfg = VectorStoreConfig(provider="faiss", config={})
+        assert "Application Support/mem0" in cfg.config.path
+
+
+@pytest.mark.skipif(sys.platform != "linux", reason="Linux-specific default")
+def test_linux_default_respects_xdg_data_home():
+    with patch.dict(os.environ, {"XDG_DATA_HOME": "/custom/xdg"}):
+        os.environ.pop("MEM0_DATA_DIR", None)
+        cfg = VectorStoreConfig(provider="faiss", config={})
+        assert cfg.config.path == os.path.join("/custom/xdg", "mem0", "faiss")