fix: Windows file artifact URI path normalization

Merge #5523

Closes #5486

## Summary

This PR fixes Windows handling of local `file://` artifact URIs.

Both `google/adk/cli/service_registry.py` and `google/adk/artifacts/file_artifact_service.py` were passing URI-style paths into `Path(...)` without Windows URI-to-filesystem normalization. On Windows, this can produce malformed drive-relative paths such as `C:foo` instead of absolute paths like `C:\foo`.

This change applies `url2pathname()` under `os.name == "nt"` in both locations so canonical file URIs like `file:///C:/...` are converted to proper native Windows paths before constructing `Path(...)`.

## Validation

Manually tested on Windows with:

1. current working directory on `C:` and artifact target on `C:`
   - before the patch, the bug reproduced and the artifact root was created in the wrong location
   - after the patch, the artifact root was created in the intended location

2. current working directory on `C:` and artifact target on `D:`
   - before the patch, the current code could appear to work
   - after the patch, it still worked, now through correct URI-to-path normalization

3. paths containing spaces
   - after the patch, the artifact root was created correctly in the intended directory

I also verified the drive-relative behavior separately with:

```python
import ntpath

print(ntpath.abspath("C:foo"))
print(ntpath.abspath("D:foo"))
```

With current working directory `C:\Users\user1\projects\agent1`, this produced:

```text
C:\Users\user1\projects\agent1\foo
D:\foo
```

This matches the observed issue: without Windows-specific normalization, the malformed URI-derived path can behave like a drive-relative path such as `C:foo` instead of a proper absolute path like `C:\foo`.

## Notes

I have not added a regression test in this PR yet. I can add one in a follow-up if maintainers prefer a specific test location for this path-conversion logic.

Co-authored-by: George Weale <gweale@google.com>
COPYBARA_INTEGRATE_REVIEW=#5523 from cyrus-mz:fix/windows-file-artifact-uri e93847b
PiperOrigin-RevId: 943367471

Author: 2 people

src/google/adk/artifacts/file_artifact_service.py

@@ -25,6 +25,7 @@
 from typing import Union
 from urllib.parse import unquote
 from urllib.parse import urlparse
+from urllib.request import url2pathname
 
 from google.genai import types
 from pydantic import alias_generators
@@ -59,7 +60,10 @@ def _file_uri_to_path(uri: str) -> Optional[Path]:
   parsed = urlparse(uri)
   if parsed.scheme != "file":
     return None
-  return Path(unquote(parsed.path))
+  path_str = unquote(parsed.path)
+  if os.name == "nt":
+    path_str = url2pathname(path_str)
+  return Path(path_str)
 
 
 _USER_NAMESPACE_PREFIX = "user:"

src/google/adk/cli/service_registry.py

@@ -72,6 +72,7 @@ def my_session_factory(uri: str, **kwargs):
 from typing import Protocol
 from urllib.parse import unquote
 from urllib.parse import urlparse
+from urllib.request import url2pathname
 
 from ..artifacts.base_artifact_service import BaseArtifactService
 from ..memory.base_memory_service import BaseMemoryService
@@ -310,7 +311,12 @@ def file_artifact_factory(uri: str, **_):
       )
     if not parsed_uri.path:
       raise ValueError("file:// artifact URIs must include a path component.")
-    artifact_path = Path(unquote(parsed_uri.path))
+
+    artifact_path_str = unquote(parsed_uri.path)
+    if os.name == "nt":
+      artifact_path_str = url2pathname(artifact_path_str)
+
+    artifact_path = Path(artifact_path_str)
     return FileArtifactService(root_dir=artifact_path)
 
   registry.register_artifact_service("memory", memory_artifact_factory)

tests/unittests/artifacts/test_artifact_service.py

@@ -20,6 +20,7 @@
 import enum
 import json
 from pathlib import Path
+from types import SimpleNamespace
 from typing import Any
 from typing import Optional
 from typing import Union
@@ -28,6 +29,7 @@
 from urllib.parse import unquote
 from urllib.parse import urlparse
 
+from google.adk.artifacts import file_artifact_service
 from google.adk.artifacts.base_artifact_service import ArtifactVersion
 from google.adk.artifacts.base_artifact_service import ensure_part
 from google.adk.artifacts.file_artifact_service import FileArtifactService
@@ -1591,3 +1593,25 @@ async def test_save_load_empty_text_artifact(
   assert loaded is not None
   assert loaded.text == ""
   assert loaded.inline_data is None
+
+
+def test_file_uri_to_path_normalizes_windows_file_uri(monkeypatch):
+  monkeypatch.setattr(file_artifact_service, "os", SimpleNamespace(name="nt"))
+  mocked_url2pathname = mock.Mock(return_value=r"C:\tmp\adk artifacts")
+  monkeypatch.setattr(
+      file_artifact_service, "url2pathname", mocked_url2pathname
+  )
+
+  result = file_artifact_service._file_uri_to_path(
+      "file:///C:/tmp/adk%20artifacts"
+  )
+
+  mocked_url2pathname.assert_called_once_with("/C:/tmp/adk artifacts")
+  assert result == Path(r"C:\tmp\adk artifacts")
+
+
+def test_file_uri_to_path_returns_none_for_non_file_uri():
+  assert (
+      file_artifact_service._file_uri_to_path("gs://bucket/adk_artifacts")
+      is None
+  )

tests/unittests/cli/test_service_registry.py

@@ -12,8 +12,12 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from pathlib import Path
+from types import SimpleNamespace
+from unittest import mock
 from unittest.mock import patch
 
+from google.adk.cli import service_registry
 import pytest
 
 
@@ -124,6 +128,33 @@ def test_create_artifact_service_gcs(registry, mock_services):
   )
 
 
+def test_file_artifact_factory_normalizes_windows_file_uri(monkeypatch):
+  monkeypatch.setattr(service_registry, "os", SimpleNamespace(name="nt"))
+  mocked_url2pathname = mock.Mock(return_value=r"C:\tmp\adk artifacts")
+  monkeypatch.setattr(service_registry, "url2pathname", mocked_url2pathname)
+
+  registry = service_registry.ServiceRegistry()
+  service_registry._register_builtin_services(registry)
+
+  with mock.patch(
+      "google.adk.artifacts.file_artifact_service.FileArtifactService"
+  ) as mock_file_artifact_service:
+    registry.create_artifact_service("file:///C:/tmp/adk%20artifacts")
+
+  mocked_url2pathname.assert_called_once_with("/C:/tmp/adk artifacts")
+  mock_file_artifact_service.assert_called_once_with(
+      root_dir=Path(r"C:\tmp\adk artifacts")
+  )
+
+
+def test_file_artifact_factory_rejects_non_local_authority():
+  registry = service_registry.ServiceRegistry()
+  service_registry._register_builtin_services(registry)
+
+  with pytest.raises(ValueError, match="local filesystem"):
+    registry.create_artifact_service("file://example.com/tmp/adk_artifacts")
+
+
 # Memory Service Tests
 @patch("google.adk.cli.utils.envs.load_dotenv_for_agent")
 def test_create_memory_service_rag(