Node settings arrive as keyword arguments, not a params dict

A python node's settings are constants of its own function, so they are passed
the way its ports are: by name. The controller binds them to the compiled
function, the `params` field is gone from the worker and remote protocols, and
a setting sharing a port's name is reported as a node error rather than
shadowing it. The panel's scaffold follows suit and keeps the header in step
with both ports and settings.

The demo's `pace` moves from a flow input to a setting of the training node,
which is what it always was.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NUb8YpL2s3gmN9WTACTt4q

backend/tests/flow/test_node_settings.py

@@ -0,0 +1,63 @@
+"""A node's settings are arguments of its function, like its ports.
+
+What distinguishes them is where the value comes from: a port carries whatever
+the graph last published, a setting is a constant stored with the flow. Both
+arrive by name, so one name cannot mean both.
+"""
+
+from pathlib import Path
+
+import pytest
+
+from app.flow.controller import FlowController
+from app.flow.messages import DType, MessageSpec
+from app.flow.pipeline import Pipeline
+from app.flow.schemas import FlowDef, NodeDef
+from app.flow.state import MemoryState
+from app.flow.store import FlowStore
+
+SOURCE = "def process(reading, factor):\n    return {'scaled': reading * factor}\n"
+
+
+def a_flow(**params: object) -> FlowDef:
+    return FlowDef(
+        name="house",
+        nodes=[
+            NodeDef(
+                id="scale",
+                params=dict(params),
+                requires=[MessageSpec(name="reading", dtype=DType.FLOAT)],
+                provides=[MessageSpec(name="scaled", dtype=DType.FLOAT)],
+            )
+        ],
+    )
+
+
+@pytest.fixture
+def store(tmp_path: Path) -> FlowStore:
+    return FlowStore(tmp_path / "flows")
+
+
+def test_a_setting_reaches_the_function_as_a_keyword_argument(store: FlowStore):
+    store.write_flow(a_flow(factor=3))
+    store.write_node_source("house", "scale", SOURCE)
+    controller = FlowController(store)
+
+    nodes, _loaded, _initial, _inputs = controller._build_flows(
+        [(store.read_flow("house"), False)]
+    )
+    pipeline = Pipeline(nodes=nodes, state=MemoryState())
+    pipeline.run({"house.reading": 2.0})
+
+    assert pipeline.values()["house.scaled"]["value"] == 6.0
+
+
+def test_a_setting_named_after_a_port_is_refused(store: FlowStore):
+    store.write_draft(a_flow(reading=3), 0)
+    store.write_node_source("house", "scale", SOURCE, draft=True)
+    controller = FlowController(store)
+
+    preview = controller.preview("house")
+
+    assert [node.status for node in preview.nodes] == ["error"]
+    assert "both an input and a setting" in (preview.nodes[0].error or "")