fix: support reusing field-input components in event-driven flows

plugboard-schemas/plugboard_schemas/_validation.py

@@ -18,6 +18,9 @@
 from ._validator_registry import validator
 
 
+_SYSTEM_STOP_EVENT = "system_stop"
+
+
 def _build_component_graph(
     connectors: dict[str, dict[str, _t.Any]],
 ) -> dict[str, set[str]]:
@@ -98,9 +101,11 @@ def validate_all_inputs_connected(
     for comp_name, comp_data in components.items():
         io = comp_data.get("io", {})
         all_inputs = set(io.get("inputs", []))
+        input_events = set(io.get("input_events", []))
+        has_non_system_input_events = bool(input_events - {_SYSTEM_STOP_EVENT})
         connected = connected_inputs.get(comp_name, set())
         unconnected = all_inputs - connected
-        if unconnected:
+        if unconnected and not has_non_system_input_events:
             errors.append(f"Component '{comp_name}' has unconnected inputs: {sorted(unconnected)}")
     return errors
 

plugboard/component/component.py

@@ -345,6 +345,11 @@ async def _wrapper() -> None:
             with self._job_id_ctx():
                 await self._set_status(Status.RUNNING, publish=not self._is_running)
                 await self._io_read_with_status_check()
+                # IO can close here once all producers for the component's event-only inputs have
+                # finished emitting. Return before rebinding inputs so the last event-populated
+                # field values are not replayed as if they were fresh inputs in another step.
+                if self.io.is_closed:
+                    return
                 await self._handle_events()
                 self._bind_inputs()
                 if self._can_step:
@@ -365,6 +370,11 @@ async def _wrapper() -> None:
     def _has_field_inputs(self) -> bool:
         return len(self.io.inputs) > 0
 
+    @property
+    def _has_connected_field_inputs(self) -> bool:
+        """Whether any declared field inputs are connected via input channels."""
+        return self.io.has_connected_field_inputs
+
     @cached_property
     def _has_event_inputs(self) -> bool:
         input_events = set([evt.safe_type() for evt in self.io.input_events])
@@ -409,7 +419,7 @@ async def _io_read_with_status_check(self) -> None:
             task.cancel()
         for task in done:
             exc = task.exception()
-            if isinstance(exc, EventStreamClosedError) and len(self.io.inputs) == 0:
+            if isinstance(exc, EventStreamClosedError) and not self._has_connected_field_inputs:
                 await self.io.close()  # Call close for final wait and flush event buffer
             elif exc is not None:
                 raise exc
@@ -422,7 +432,7 @@ async def _periodic_status_check(self) -> None:
             # TODO : Eventually producer graph update will be event driven. For now,
             #      : the update is performed periodically, so it's called here along
             #      : with the status check.
-            if len(self.io.inputs) == 0:
+            if not self._has_connected_field_inputs:
                 await self._update_producer_graph()
 
     async def _status_check(self) -> None:

plugboard/component/io_controller.py

@@ -86,8 +86,9 @@ def is_closed(self) -> bool:
         """Returns `True` if the `IOController` is closed, `False` otherwise."""
         return self._is_closed
 
-    @cached_property
-    def _has_field_inputs(self) -> bool:
+    @property
+    def has_connected_field_inputs(self) -> bool:
+        """Returns whether any field inputs are connected via channels."""
         return len(self._input_channels) > 0
 
     @cached_property
@@ -96,7 +97,7 @@ def _has_event_inputs(self) -> bool:
 
     @cached_property
     def _has_inputs(self) -> bool:
-        return self._has_field_inputs or self._has_event_inputs
+        return self.has_connected_field_inputs or self._has_event_inputs
 
     async def read(self, timeout: float | None = None) -> None:
         """Reads data and/or events from input channels.
@@ -139,7 +140,7 @@ async def read(self, timeout: float | None = None) -> None:
 
     def _set_read_tasks(self) -> list[asyncio.Task]:
         read_tasks: list[asyncio.Task] = []
-        if self._has_field_inputs:
+        if self.has_connected_field_inputs:
             if _fields_read_task not in self._read_tasks:
                 read_fields_task = asyncio.create_task(self._read_fields(), name=_fields_read_task)
                 self._read_tasks[_fields_read_task] = read_fields_task
@@ -374,7 +375,7 @@ def _add_channel_for_event(
 
     def _create_input_field_group_tasks(self) -> None:
         """Groups input field channels by field name and launches read tasks for group inputs."""
-        if not self._has_field_inputs:
+        if not self.has_connected_field_inputs:
             return
         field_channels: dict[str, list[tuple[_t_field_key, Channel]]] = defaultdict(list)
         for key, chan in self._input_channels.items():

tests/integration/test_process_with_components_run.py

@@ -23,6 +23,7 @@
 )
 from plugboard.events import Event
 from plugboard.exceptions import ConstraintError, NotInitialisedError, ProcessStatusError
+from plugboard.library import FileWriter
 from plugboard.process import LocalProcess, Process, RayProcess
 from plugboard.schemas import ConnectorSpec, Status
 from tests.conftest import ComponentTestHelper, zmq_connector_cls
@@ -459,6 +460,85 @@ async def test_event_driven_process_shutdown(
     await process.destroy()
 
 
+class MessageEventData(BaseModel):
+    """Data for a message event."""
+
+    message: str
+
+
+class MessageEvent(Event):
+    """Event carrying a file-writer message."""
+
+    type: _t.ClassVar[str] = "message_event"
+    data: MessageEventData
+
+
+class MessageEventGenerator(ComponentTestHelper):
+    """Produces a fixed number of message events."""
+
+    io = IO(output_events=[MessageEvent])
+
+    def __init__(self, iters: int, *args: _t.Any, **kwargs: _t.Any) -> None:
+        super().__init__(*args, **kwargs)
+        self._iters = iters
+
+    async def init(self) -> None:
+        await super().init()
+        self._seq = iter(range(self._iters))
+
+    async def step(self) -> None:
+        try:
+            idx = next(self._seq)
+        except StopIteration:
+            await self.io.close()
+        else:
+            evt = MessageEvent(
+                source=self.name,
+                data=MessageEventData(message=f"Message {idx}"),
+            )
+            self.io.queue_event(evt)
+            await super().step()
+
+
+class EventReaderFileWriter(FileWriter):
+    """`FileWriter` variant that adds event handling instead of a connector for `message`."""
+
+    io = IO(input_events=[MessageEvent])
+
+    @MessageEvent.handler
+    async def handle_message(self, event: MessageEvent) -> None:
+        self.message = event.data.message
+
+
+@pytest.mark.asyncio
+async def test_event_driven_file_writer_reuse(tmp_path: Path) -> None:
+    """Test that field-input components can be reused in event-driven processes."""
+    output_path = tmp_path / "output_messages.csv"
+    components = [
+        MessageEventGenerator(iters=3, name="message_event_generator"),
+        EventReaderFileWriter(
+            path=output_path,
+            name="event_reader_file_writer",
+            field_names=["message"],
+        ),
+    ]
+    event_connectors = AsyncioConnector.builder().build_event_connectors(components)
+    process = LocalProcess(components=components, connectors=event_connectors)
+
+    await process.init()
+    await process.run()
+
+    assert process.status == Status.COMPLETED
+    assert output_path.read_text().splitlines() == [
+        "message",
+        "Message 0",
+        "Message 1",
+        "Message 2",
+    ]
+
+    await process.destroy()
+
+
 _SHORT_TIMEOUT = 0.1
 
 

tests/unit/test_process_validation.py

@@ -303,6 +303,21 @@ def test_no_inputs_no_errors(self) -> None:
         errors = validate_all_inputs_connected(pd)
         assert errors == []
 
+    def test_missing_inputs_allowed_for_event_driven_component_reuse(self) -> None:
+        """Unconnected inputs are allowed when non-system input events can populate them."""
+        pd = _make_process_dict(
+            components={
+                "producer": _make_component("producer", output_events=["message_event"]),
+                "writer": _make_component(
+                    "writer",
+                    inputs=["message"],
+                    input_events=["system_stop", "message_event"],
+                ),
+            },
+        )
+        errors = validate_all_inputs_connected(pd)
+        assert errors == []
+
 
 # ---------------------------------------------------------------------------
 # Tests for validate_input_events