Give a node's fluksio module the logger the SDK exports

Inside a worker `import fluksio` is the reporter, which had emit and the
artifact calls but no logger — so `fluksio.logger.info(...)`, written
against the SDK's top-level export, died with AttributeError after the
training it was reporting on had already succeeded. Its records go to the
same capture a print does; the handler resolves sys.stderr per record
because a call runs under redirect_stderr.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019Hra4ndWMCLU5F3KjUuVAc

backend/tests/flow/test_workers.py

@@ -69,6 +69,24 @@ def test_a_node_returns_its_value_and_what_it_printed(pool, capsys):
     assert "seen 21" in capsys.readouterr().out
 
 
+def test_a_node_can_log_through_the_module_it_imports(pool, capsys):
+    """The SDK exports `logger`; inside a worker `fluksio` is the reporter.
+
+    Without it, `fluksio.logger.info(...)` died with AttributeError — after
+    the training it was reporting on had already succeeded.
+    """
+    result = run(
+        pool,
+        "import fluksio\n\n\n"
+        "def process(value):\n"
+        "    fluksio.logger.info('tuned %s', value)\n"
+        "    return {'out': value}\n",
+        value=7,
+    )
+    assert result == {"out": 7}
+    assert "tuned 7" in capsys.readouterr().out
+
+
 def test_a_failure_keeps_its_class_and_points_at_the_node(pool):
     with pytest.raises(Exception) as caught:
         run(pool, "def process():\n    raise ValueError('bad input')\n")