fix: avoid local .adk storage in Cloud Run/GKE

Default session and artifact services to in-memory when running in Cloud Run/Kubernetes (or when agents_dir isn’t writable) to prevent startup failures from attempting to create .adk under read-only/unwritable container paths (e.g. /app/agents/.adk). Local development defaults are unchanged.

  - ADK_FORCE_LOCAL_STORAGE=1 to always use .adk defaults
  - ADK_DISABLE_LOCAL_STORAGE=1 to always avoid local storage

If local artifact initialization raises PermissionError, fall back to in-memory and log a warning

Close #3907

Co-authored-by: George Weale <gweale@google.com>
PiperOrigin-RevId: 853315459

tests/unittests/cli/utils/test_cli.py

@@ -293,7 +293,10 @@ async def test_run_cli_save_session(
 
 def test_create_artifact_service_defaults_to_file(tmp_path: Path) -> None:
   """Service factory should default to FileArtifactService when URI is unset."""
-  service = create_artifact_service_from_options(base_dir=tmp_path)
+  service = create_artifact_service_from_options(
+      base_dir=tmp_path,
+      use_local_storage=True,
+  )
   assert isinstance(service, FileArtifactService)
   expected_root = Path(tmp_path) / ".adk" / "artifacts"
   assert service.root_dir == expected_root
@@ -304,7 +307,10 @@ def test_create_artifact_service_uses_shared_root(
     tmp_path: Path,
 ) -> None:
   """Artifact service should use a single file artifact service."""
-  service = create_artifact_service_from_options(base_dir=tmp_path)
+  service = create_artifact_service_from_options(
+      base_dir=tmp_path,
+      use_local_storage=True,
+  )
   assert isinstance(service, FileArtifactService)
   expected_root = Path(tmp_path) / ".adk" / "artifacts"
   assert service.root_dir == expected_root