Export FLOWS and build from the top-level fluksio package

A test of the declarations had to import them from fluksio.sdk while the
guide teaches `from fluksio import ...`. The worker's inert module gets the
same two names so a module importing them still loads inside a node.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QgG6TJw5qBZzaLghQSRVrq

backend/fluksio/__init__.py

@@ -4,7 +4,8 @@ Two audiences, one import name. In a research repository, ``from fluksio
 import Port, node, Flow`` is the authoring API: it says which of your existing
 functions are nodes and which nodes make up a flow, and ``fluksio sync``
 uploads what it finds. Those names come from :mod:`fluksio.sdk`, which imports
-nothing but the standard library.
+nothing but the standard library. ``FLOWS`` and ``build`` come with them, so a
+test can check the declarations without an engine.
 
 Inside a node, ``import fluksio`` is not this package at all: the worker
 installs a reporter of its own under that name before any node code runs, so
@@ -24,7 +25,7 @@ from importlib.metadata import PackageNotFoundError
 from importlib.metadata import version as _version
 from typing import Any
 
-from fluksio.sdk import Flow, Port, node, use
+from fluksio.sdk import FLOWS, Flow, Port, build, node, use
 
 try:
     __version__ = _version("fluksio")
@@ -32,8 +33,10 @@ except PackageNotFoundError:  # pragma: no cover - a checkout that was never ins
     __version__ = "0.0.0+unknown"
 
 __all__ = [
+    "FLOWS",
     "Flow",
     "Port",
+    "build",
     "emit",
     "load_artifact",
     "node",

backend/tests/sdk/test_build.py

@@ -364,3 +364,15 @@ def test_a_node_in_a_script_run_directly_is_refused_at_sync_not_at_import():
         flow.document()
     with pytest.raises(SyncError, match="run directly"):
         flow.shims()
+
+
+def test_the_registry_and_the_builder_come_with_the_authoring_import():
+    """A test of the declarations needs no second import path."""
+    import fluksio
+    import fluksio.sdk
+
+    flow = a_flow()
+
+    assert fluksio.FLOWS is fluksio.sdk.FLOWS
+    assert fluksio.FLOWS["train"] is flow
+    assert fluksio.build(flow) == fluksio.sdk.build(flow)