A supervised loop that crashes reports its node down

A push session that failed before it listened left only a task_crashed
event. The wrapper in _run_supervised now reports down with the exception,
unless the loop already said why it is down.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WgBfkm4rCmtd1T4vHWjEPx

backend/tests/flow/test_connector.py

@@ -14,6 +14,7 @@ from fluksio.flow.messages import DType, MessageSpec
 from fluksio.flow.nodes import Node
 from fluksio.flow.pipeline import Pipeline
 from fluksio.flow.plugins import load_plugins
+from fluksio.flow.supervision import Supervisor
 
 
 class Sensor(ConnectorNode):
@@ -156,6 +157,35 @@ def test_an_undeclared_port_keeps_failing_until_the_node_declares_it():
     assert len([entry for entry in health if entry[0] == "down"]) > 1
 
 
+def test_a_push_session_that_fails_before_it_listens_reports_down():
+    """A crashed loop is node health, not only a crash event."""
+
+    class Push(Sensor):
+        async def start(self, app: Any = None) -> None:
+            self._run_supervised("push", self._session)
+
+        async def _session(self) -> None:
+            raise ConnectionError("bridge unreachable")
+
+    health: list[tuple[str, str | None]] = []
+    node = Push(provides=[MessageSpec(name="reading", dtype=DType.FLOAT)])
+    node.assign_flow("demo", "push")
+    node._on_health = lambda _node, status, detail: health.append((status, detail))
+
+    async def scenario() -> None:
+        node.supervisor = Supervisor()
+        await node.start()
+        for _ in range(500):
+            if health:
+                break
+            await asyncio.sleep(0.01)
+        await node.supervisor.cancel_all()
+
+    asyncio.run(scenario())
+
+    assert health == [("down", "ConnectionError: bridge unreachable")]
+
+
 class Actuator(ConnectorNode):
     """A connector that commands something instead of reading it."""