Starting a running flow restarts its nodes, so interval and cron Injects keep firing; a params-dict node is told settings arrive by name

backend/fluksio/flow/controller.py

@@ -659,13 +659,19 @@ class FlowController:
         await self._acquire(FLOW_REBUILD_WAIT)
         try:
             if enabled:
+                running = flow not in self.disabled
                 # The gate first: a subscription that fires the instant it
                 # starts must not be turned away by a flag on its way out.
                 self.disabled = self.disabled - {flow}
                 self.pipeline.set_disabled(self.disabled)
                 # Lifts any quarantine, which is what a rebuild used to do by
-                # throwing the whole supervisor away.
-                await self.supervisor.cancel_flow(flow)
+                # throwing the whole supervisor away. A running flow's nodes
+                # are stopped first: a node already started returns from
+                # start() at once, which would leave its cancelled loop dead.
+                if running:
+                    await self._teardown(flow)
+                else:
+                    await self.supervisor.cancel_flow(flow)
                 await self._activate(flow)
             else:
                 self.disabled = self.disabled | {flow}
@@ -1989,10 +1995,14 @@ def _signature_gap(
     if not missing:
         return None
     kind = "an input" if missing[0] in ports else "a setting"
-    return (
+    gap = (
         f"'{missing[0]}' is {kind} of '{node_id}' but "
         f"process({', '.join(names)}) takes no such argument"
     )
+    if kind == "a setting" and "params" in names:
+        # Code written for the `params` dict settings used to arrive in.
+        gap += f". Settings arrive by name: process(..., {missing[0]})"
+    return gap
 
 
 def follow_header(node: NodeDef, code: str, drop: bool = True) -> NodeDef:

backend/tests/flow/test_node_settings.py

@@ -9,7 +9,7 @@ from pathlib import Path
 
 import pytest
 
-from fluksio.flow.controller import FlowController, follow_header
+from fluksio.flow.controller import FlowController, _signature_gap, follow_header
 from fluksio.flow.messages import DType, MessageSpec
 from fluksio.flow.pipeline import Pipeline
 from fluksio.flow.schemas import FlowDef, NodeDef
@@ -226,3 +226,13 @@ def test_a_header_it_cannot_read_for_certain_leaves_the_node():
         "def run(value): pass\n",
     ):
         assert follow_header(node, code) == node
+
+
+def test_code_written_for_the_params_dict_is_told_settings_arrive_by_name():
+    gap = _signature_gap("def process(a, params): pass\n", "n", {"a"}, {"target"})
+
+    assert gap is not None
+    assert "process(..., target)" in gap
+    assert (
+        _signature_gap("def process(a, target): pass\n", "n", {"a"}, {"target"}) is None
+    )

backend/tests/flow/test_runtime_control.py

@@ -331,6 +331,12 @@ def test_stopping_one_flow_does_not_touch_the_others(
         assert lifecycle == ["start a.io"]
         assert {name: engine.loaded[name].node for name in ("a.io", "b.io")} == before
 
+        # Started while running is a restart: the cancelled loops come back.
+        lifecycle.clear()
+        await engine.set_enabled("a", True)
+
+        assert lifecycle == ["stop a.io", "start a.io"]
+
     asyncio.run(asyncio.wait_for(scenario(), timeout=10))