feat(filesystem): add multi-root local folder support in backend

surfsense_backend/tests/unit/middleware/test_filesystem_backends.py

@@ -8,7 +8,9 @@ from app.agents.new_chat.filesystem_selection import (
     FilesystemMode,
     FilesystemSelection,
 )
-from app.agents.new_chat.middleware.local_folder_backend import LocalFolderBackend
+from app.agents.new_chat.middleware.multi_root_local_folder_backend import (
+    MultiRootLocalFolderBackend,
+)
 
 pytestmark = pytest.mark.unit
 
@@ -17,16 +19,16 @@ class _RuntimeStub:
     state = {"files": {}}
 
 
-def test_backend_resolver_returns_local_backend_for_local_mode(tmp_path: Path):
+def test_backend_resolver_returns_multi_root_backend_for_single_root(tmp_path: Path):
     selection = FilesystemSelection(
         mode=FilesystemMode.DESKTOP_LOCAL_FOLDER,
         client_platform=ClientPlatform.DESKTOP,
-        local_root_path=str(tmp_path),
+        local_root_paths=(str(tmp_path),),
     )
     resolver = build_backend_resolver(selection)
 
     backend = resolver(_RuntimeStub())
-    assert isinstance(backend, LocalFolderBackend)
+    assert isinstance(backend, MultiRootLocalFolderBackend)
 
 
 def test_backend_resolver_uses_cloud_mode_by_default():
@@ -35,3 +37,19 @@ def test_backend_resolver_uses_cloud_mode_by_default():
     # StateBackend class name check keeps this test decoupled
     # from internal deepagents runtime class identity.
     assert backend.__class__.__name__ == "StateBackend"
+
+
+def test_backend_resolver_returns_multi_root_backend_for_multiple_roots(tmp_path: Path):
+    root_one = tmp_path / "resume"
+    root_two = tmp_path / "notes"
+    root_one.mkdir()
+    root_two.mkdir()
+    selection = FilesystemSelection(
+        mode=FilesystemMode.DESKTOP_LOCAL_FOLDER,
+        client_platform=ClientPlatform.DESKTOP,
+        local_root_paths=(str(root_one), str(root_two)),
+    )
+    resolver = build_backend_resolver(selection)
+
+    backend = resolver(_RuntimeStub())
+    assert isinstance(backend, MultiRootLocalFolderBackend)