The drop-sync refactor is now contractually enforced:
* create_storage({"mode": "sync"|"async"|<any>}) raises StorageConfigError
-- the regression we most want to catch is someone "restoring" the
sync shape by re-introducing mode= handling.
* create_storage() preserves caller's dict, returns an AsyncStorageBackend
subclass, and wraps constructor TypeError into a useful StorageConfigError.
* build_storage_config emits no mode key on either local or s3 branch.
* register_backend() refuses to silently overwrite a different class on
the same name (collision guard), and accepts same-class re-registration.
* registry surfaces the built-in local + s3 classes after import; the
conflict-test cleanup pattern avoids leaking global state across tests.
Adds [tool.pytest.ini_options] (asyncio_mode=auto, testpaths=tests) so
uv run --package common pytest common/tests works from the workspace root.
17 new tests, all green. Backend suite still 136 passed.
tao.chen
24f40b5dd7