feat: isolate default sqlite db by config dir (#567)

Signed-off-by: phernandez <paul@basicmachines.co>

Author: phernandez

src/basic_memory/config.py

@@ -397,8 +397,11 @@ def app_database_path(self) -> Path:
 
         This is the single database that will store all knowledge data
         across all projects.
+
+        Uses BASIC_MEMORY_CONFIG_DIR when set so each process/worktree can
+        isolate both config and database state.
         """
-        database_path = Path.home() / DATA_DIR_NAME / APP_DATABASE_NAME
+        database_path = self.data_dir_path / APP_DATABASE_NAME
         if not database_path.exists():  # pragma: no cover
             database_path.parent.mkdir(parents=True, exist_ok=True)
             database_path.touch()
@@ -447,8 +450,13 @@ def ensure_project_paths_exists(self) -> "BasicMemoryConfig":  # pragma: no cove
         return self
 
     @property
-    def data_dir_path(self):
-        return Path.home() / DATA_DIR_NAME
+    def data_dir_path(self) -> Path:
+        """Get app state directory for config and default SQLite database."""
+        if config_dir := os.getenv("BASIC_MEMORY_CONFIG_DIR"):
+            return Path(config_dir)
+
+        home = os.getenv("HOME", Path.home())
+        return Path(home) / DATA_DIR_NAME
 
 
 # Module-level cache for configuration

tests/test_config.py

@@ -97,6 +97,25 @@ def test_basic_memory_home_overrides_existing_main_project(self, config_home, mo
         # Note: This tests the current behavior where default_factory takes precedence
         assert config.projects["main"] == original_path
 
+    def test_app_database_path_uses_custom_config_dir(self, tmp_path, monkeypatch):
+        """Default SQLite DB should live under BASIC_MEMORY_CONFIG_DIR when set."""
+        custom_config_dir = tmp_path / "instance-a" / "state"
+        monkeypatch.setenv("BASIC_MEMORY_CONFIG_DIR", str(custom_config_dir))
+
+        config = BasicMemoryConfig(projects={"main": str(tmp_path / "project")})
+
+        assert config.data_dir_path == custom_config_dir
+        assert config.app_database_path == custom_config_dir / "memory.db"
+        assert config.app_database_path.exists()
+
+    def test_app_database_path_defaults_to_home_data_dir(self, config_home, monkeypatch):
+        """Without BASIC_MEMORY_CONFIG_DIR, default DB stays at ~/.basic-memory/memory.db."""
+        monkeypatch.delenv("BASIC_MEMORY_CONFIG_DIR", raising=False)
+        config = BasicMemoryConfig()
+
+        assert config.data_dir_path == config_home / ".basic-memory"
+        assert config.app_database_path == config_home / ".basic-memory" / "memory.db"
+
 
 class TestConfigManager:
     """Test ConfigManager functionality."""