fix: prevent nested project paths to avoid data conflicts (#338)

Signed-off-by: phernandez <paul@basicmachines.co>
Co-authored-by: Claude <noreply@anthropic.com>

src/basic_memory/services/project_service.py

@@ -88,6 +88,40 @@ class ProjectService:
             name
         )
 
+    def _check_nested_paths(self, path1: str, path2: str) -> bool:
+        """Check if two paths are nested (one is a prefix of the other).
+
+        Args:
+            path1: First path to compare
+            path2: Second path to compare
+
+        Returns:
+            True if one path is nested within the other, False otherwise
+
+        Examples:
+            _check_nested_paths("/foo", "/foo/bar")     # True (child under parent)
+            _check_nested_paths("/foo/bar", "/foo")     # True (parent over child)
+            _check_nested_paths("/foo", "/bar")         # False (siblings)
+        """
+        # Normalize paths to ensure proper comparison
+        p1 = Path(path1).resolve()
+        p2 = Path(path2).resolve()
+
+        # Check if either path is a parent of the other
+        try:
+            # Check if p2 is under p1
+            p2.relative_to(p1)
+            return True
+        except ValueError:
+            # Not nested in this direction, check the other
+            try:
+                # Check if p1 is under p2
+                p1.relative_to(p2)
+                return True
+            except ValueError:
+                # Not nested in either direction
+                return False
+
     async def add_project(self, name: str, path: str, set_default: bool = False) -> None:
         """Add a new project to the configuration and database.
 
@@ -142,6 +176,29 @@ class ProjectService:
         else:
             resolved_path = Path(os.path.abspath(os.path.expanduser(path))).as_posix()
 
+        # Check for nested paths with existing projects
+        existing_projects = await self.list_projects()
+        for existing in existing_projects:
+            if self._check_nested_paths(resolved_path, existing.path):
+                # Determine which path is nested within which for appropriate error message
+                p_new = Path(resolved_path).resolve()
+                p_existing = Path(existing.path).resolve()
+
+                # Check if new path is nested under existing project
+                if p_new.is_relative_to(p_existing):
+                    raise ValueError(
+                        f"Cannot create project at '{resolved_path}': "
+                        f"path is nested within existing project '{existing.name}' at '{existing.path}'. "
+                        f"Projects cannot share directory trees."
+                    )
+                else:
+                    # Existing project is nested under new path
+                    raise ValueError(
+                        f"Cannot create project at '{resolved_path}': "
+                        f"existing project '{existing.name}' at '{existing.path}' is nested within this path. "
+                        f"Projects cannot share directory trees."
+                    )
+
         # First add to config file (this will validate the project doesn't exist)
         project_config = self.config_manager.add_project(name, resolved_path)