Let a connector write, and publish strings bare

Two things stopped the engine commanding this house. ConnectorNode hardwired
its node function to a no-op, so an input message reaching a connector was
discarded and Art-Net's packet builder was unreachable; write() now carries
the input ports, which is additive so the contract version holds. And the MQTT
publisher JSON-encoded every payload, so "ON" went on the wire quoted and the
devices on a shared broker, which speak bare values, ignored it.

seed_house_control.py is the rig: a flow that drives the washing machine plug,
a dimmer and a colour fixture over MQTT, carries the same two as DMX on an
Art-Net node with transmit still off, and a dashboard to drive it by hand.

Makefile

@@ -3,7 +3,7 @@
 # The workspace root delegates to these (see ../Makefile).
 
 .PHONY: dev-utils dev dev-local up down update install dev-backend dev-frontend \
-        generate-client seed-example seed-demo seed-hosted-demo test test-backend test-frontend soak bench-startup lint lint-backend \
+        generate-client seed-example seed-demo seed-house seed-hosted-demo test test-backend test-frontend soak bench-startup lint lint-backend \
         lint-frontend umami clean help
 
 COMPOSE_ROOT := $(CURDIR)
@@ -97,6 +97,9 @@ seed-example:  ## Seed the querying-chart example (needs a running stack + Influ
 seed-demo:  ## Seed the training-run example: a batch flow and its dashboard
 	cd backend && uv run python ../scripts/seed_demo_training.py
 
+seed-house:  ## Seed the house write-path rig (needs the real broker reachable)
+	cd backend && uv run python ../scripts/seed_house_control.py
+
 # Operators of the hosted demo only — NOT part of any deployment, and nothing a
 # self-hosted instance needs. It wipes and recreates its three flows and its
 # dashboard, so re-running it is how the public demo is reset.

NOTEPAD.md

@@ -60,9 +60,33 @@ Postgres + Redis + git-files split stays; the actionable part is durability.
 Needs someone watching the real hardware, so it is not a background task. This
 is what M4 still waits on, together with porting the flows.
 
-- FEAT/NODE: the connectors only read. Enable the write paths with someone watching: WF-RAC `setAirconStat` (needs an operatorId registered with the unit first, which is itself a write) and Art-Net `transmit`.
+Art-Net can write now: `ConnectorNode.write` carries a node's input ports, a
+per-port `channels` map places each on its own DMX channel, and `transmit`
+still gates the socket. Verified on the wire against a listener (channel 33 =
+255, channel 31 = 60, nothing else set) and the MQTT half was driven end to
+end against the house broker. The rig is the `house_control` flow and its
+dashboard, seeded by `make -C app seed-house`.
+
+- FEAT/NODE: Art-Net against the real fixtures is still untried. The house's own dmxnet sender re-emits universe 1 every 1000 ms, so fluksio and Node-RED overwrite each other; the test needs Node-RED's Art-Net sender stopped, and while it is stopped every channel fluksio does not set is dark.
+- FEAT/NODE: the WF-RAC write path stays gated. `setAirconStat` needs an operatorId registered with the unit first, which is itself a write, and the aircon is not on the safe-to-control list.
 - FEAT/NODE: the second WF-RAC unit (the one Node-RED addresses with operatorId "0") closes the connection on an anonymous read. It likely wants an account registered; the first unit answers without one.
 - CHORE/NODE: `wfrac` reports `mode` as "unknown" while the unit is off, because the mode bits hold a value outside the known set. Faithful to the reference decoder, but "off" would read better.
+- PERF/NODE: `ArtNetOut.write` sends one frame per input port, so a node with two ports emits two frames per run. The last one carries both channels, so the end state is right; folding them into one send would halve the traffic.
+- CHORE/NODE: the Art-Net node starts from an all-zero universe and has no way to learn what the fixtures are currently at — Art-Net has no read-back. Taking over a universe therefore blanks everything the flow does not drive. A baseline setting, or driving every channel, is what a real cutover needs.
+
+### Porting the Node-RED flows
+
+What the reference actually does, extracted while building the write-path rig.
+One `Art-Net Out` node in 865 covers every physical device: `mqtt in <topic>`
+-> `change` (msg.topic = DMX channel) -> an `nCH` encoder function -> Art-Net,
+to the Art-Net node's address universe 1. Payloads are bare: `ON`/`OFF`, a number, `[h,s,v]`,
+`UP`/`DOWN`. Nothing is retained, so state lives only in Node-RED globals and
+is lost on its restart.
+
+- CHORE/FLOW: three DMX channel collisions in the reference — ch 9 (`light/bathRoomLight` vs `light/bathRoomSinkLight`), ch 28 (`actor/windowOpenerStorage` 28-29 vs `light/traverseAmbientLight` 28-30), ch 129 (`actor/canopy` 129-130 vs an orphaned 1CH mapping). Decide these deliberately rather than porting them.
+- CHORE/FLOW: 1CH values are not scaled. `light/traverseSpotLight` and `light/kitchenDirectLight` receive 0-100 and that number lands on DMX as-is, so those fixtures never go above 100/255. The 4CH "A" channel gets `v` raw for the same reason. Faithful is ugly; deliberate is better.
+- BUG/FLOW: the reference's `function 9`/`function 10` publish the string `"undefined"` for unselected zones (`var a, b, c = [0,0,0]` only initialises `c`), which reaches the 3CH/4CH encoders and produces `NaN` DMX values. A port should emit an explicit `OFF`.
+- CHORE/FLOW: dead in the reference and not worth porting — the `AmbientModeToLight` chain, the four Dashboard toggle chains, `light/generalLight` (written, no consumer), `light/outdoorPavillonLight` (no wiring), `Color Adapt`.
 
 ### Bugs found while building the screens
 

ROADMAP.md

@@ -73,9 +73,15 @@ external interfaces. See `docs/architecture/structure.canvas` → *Backend – M
       `connector-skeleton/`. The registry follows later
 - [x] First real connectors written against that contract from outside the engine:
       WF-RAC aircon, calendar, UniFi presence and Art-Net, in `connectors/`.
-      Built by `make connectors` and installed into the image. Reading only for
+      Built by `make connectors` and installed into the image. Three of the four
-      now — the aircon package cannot produce a command and Art-Net keeps its
+      read only; the aircon package still cannot produce a command
-      packets off the wire until `transmit` is switched on
+- [x] The other direction of the contract: `ConnectorNode.write` receives the
+      node's input ports, so a connector can command something rather than only
+      read it. Additive, so `CONTRACT_VERSION` stays at 1 — before this the base
+      class discarded every message reaching a connector, which made `artnet`'s
+      packet builder unreachable. Art-Net now sends: a per-port `channels` map
+      puts each input on its own DMX channel, `transmit` still gates the socket,
+      and one node owns one universe because a frame carries all 512 levels
 - [x] Node lifecycle as a protocol (`start`/`stop`/`report_health` on `Node`),
       replacing the controller's per-type isinstance chains — the same hooks a
       connector implements, validated on the built-in nodes first

backend/app/flow/connector.py

@@ -14,7 +14,10 @@ What a connector gets from the base class:
 * :meth:`Node.report_health`, so a connection problem shows on the node rather
   than only in the log;
 * the lifecycle hooks the controller drives, so nothing device-specific has to
-  be known by the engine.
+  be known by the engine;
+* :meth:`ConnectorNode.write`, the other direction — values arriving on the
+  node's input ports, for a connector that commands something rather than only
+  reading it.
 
 The message schemas and the parameter model are the rest of the contract, and
 they are the same ones the built-in nodes use. See ``docs/connectors/`` for the
@@ -81,16 +84,15 @@ class ConnectorNode(Node):
     __slots__ = ("config", "_poll_task", "_stop_event", "_last_published")
 
     def __init__(self, **kwargs: Any) -> None:
-        super().__init__(f=self._unused, **kwargs)
+        super().__init__(f=self._dispatch, **kwargs)
         self.config = type(self).Params(**self.params)
         self._poll_task: asyncio.Task[None] | None = None
         self._stop_event: asyncio.Event | None = None
         self._last_published: dict[str, Any] = {}
 
-    @staticmethod
+    def _dispatch(self, params: dict[str, Any], **ports: Any) -> dict[str, Any] | None:
-    def _unused(**_: Any) -> None:
+        """The scheduler's entry point. Settings are already on ``self.config``."""
-        """A connector publishes from its own loop, not from the scheduler."""
+        return self.write(**ports)
-        return None
 
     # -------------------------------------------------------------------------
     # What a connector implements
@@ -104,6 +106,18 @@ class ConnectorNode(Node):
         """
         return None
 
+    def write(self, **ports: Any) -> dict[str, Any] | None:
+        """Send incoming values to the device. Values arrive keyed by input port.
+
+        A connector that only reads leaves this alone — the default discards
+        whatever reaches it, which is what a node with no inputs gets anyway.
+        Return ``None`` unless the device answers something worth publishing,
+        in which case return it keyed by output port like :meth:`poll` does.
+
+        This runs on the scheduler's thread, so it must not block for long.
+        """
+        return None
+
     # -------------------------------------------------------------------------
     # What the engine drives
     # -------------------------------------------------------------------------

backend/app/flow/nodes/mqtt.py

@@ -379,7 +379,11 @@ class MqttNode(Node):
                 )
                 continue
 
-            payload = json.dumps(value)
+            # A string goes on the wire as it stands. Devices on a shared
+            # broker expect bare values, and the subscriber below already
+            # falls back to the raw text when it is not JSON, so a
+            # fluksio-to-fluksio round trip is unaffected.
+            payload = value if isinstance(value, str) else json.dumps(value)
             await client.publish(
                 topic,
                 payload=payload,

backend/tests/flow/test_connector.py

@@ -100,6 +100,34 @@ def test_a_failing_poll_reports_down_and_keeps_going():
     assert health[-1][0] == "ok"
 
 
+class Actuator(ConnectorNode):
+    """A connector that commands something instead of reading it."""
+
+    contract = CONTRACT_VERSION
+    title = "Test actuator"
+
+    def __init__(self, **kwargs: Any) -> None:
+        super().__init__(**kwargs)
+        self.commands: list[dict[str, Any]] = []
+
+    def write(self, **ports: Any) -> None:
+        self.commands.append(ports)
+        return None
+
+
+def test_an_incoming_message_reaches_a_connector_that_writes():
+    node = Actuator(requires=[MessageSpec(name="level", dtype=DType.INT)])
+    node.assign_flow("demo", "actuator")
+
+    assert node.execute({"demo.level": 255}) is None
+    assert node.commands == [{"level": 255}]
+
+
+def test_a_read_only_connector_ignores_what_reaches_it():
+    node = a_sensor([])
+    assert node.execute({}) is None
+
+
 def test_a_credential_param_is_marked_for_the_editor():
     schema = Sensor.Params.model_json_schema()
     assert schema["properties"]["poll_interval"]["default"] == 0

backend/tests/flow/test_senders.py

@@ -64,3 +64,28 @@ def test_a_full_publish_queue_drops_the_oldest():
         assert health == [("degraded", "publish queue full")]
 
     asyncio.run(scenario())
+
+
+def test_a_string_goes_on_the_wire_bare():
+    """Devices on a shared broker expect `ON`, not `"ON"`."""
+
+    class Recorder:
+        def __init__(self) -> None:
+            self.published: list[tuple[str, str]] = []
+
+        async def publish(self, topic, payload, **_):
+            self.published.append((topic, payload))
+
+    node = MqttNode(
+        requires=[
+            MessageSpec(name="plug", port="plug", dtype=DType.STR),
+            MessageSpec(name="level", port="level", dtype=DType.INT),
+        ],
+        params={"topic": {"plug": "actor/plug", "level": "light/level"}},
+    )
+    node.assign_flow("house", "out")
+    client = Recorder()
+
+    asyncio.run(node._publish_with(client, {"plug": "ON", "level": 60}))
+
+    assert client.published == [("actor/plug", "ON"), ("light/level", "60")]