Draw a node that is down as a troubled neuron

`brain_graph` read `self.issues` alone, which is what a build found — so a
node that loaded and then lost its device was a well neuron on Home, and
that is what someone comes to this view to find.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KYM38KSb4V4v2T71eifnZv

backend/fluksio/flow/controller.py

@@ -1497,10 +1497,12 @@ class FlowController:
         compiled pipeline, so a node that failed to load still appears — a
         broken neuron is exactly what someone comes to this view to find.
         """
-        # What validation found, by the node it names. A cycle names every node
-        # in it, so all of them are marked rather than an arbitrary one.
+        # What validation found, by the node it names, plus what is down right
+        # now — a neuron someone comes here to find is as often a node that
+        # stopped working as one that never built. A cycle names every node in
+        # it, so all of them are marked rather than an arbitrary one.
         troubled: dict[str, str] = {}
-        for issue in self.issues:
+        for issue in self.issues + self._health_issues():
             if issue.code in ADVISORY_ISSUES:
                 continue
             for member in (*issue.nodes, *filter(None, [issue.node])):

backend/tests/flow/test_brain_graph.py

@@ -9,7 +9,7 @@ from pathlib import Path
 
 import pytest
 
-from fluksio.flow.controller import FlowController
+from fluksio.flow.controller import FlowController, LoadedNode
 from fluksio.flow.messages import DType, MessageSpec
 from fluksio.flow.nodes import MqttNode
 from fluksio.flow.pipeline import ValidationIssue
@@ -105,6 +105,26 @@ def test_a_neuron_carries_what_stops_it_running(controller: FlowController):
     }
 
 
+def test_a_node_that_is_down_is_a_troubled_neuron(controller: FlowController):
+    """A node that stopped working is what someone comes to this view to find.
+
+    `self.issues` is what a build found; being down happens afterwards, so the
+    graph has to read the health issues too or a dead node draws as a well one.
+    """
+    controller.loaded["house.scale"] = LoadedNode(
+        id="house.scale",
+        flow="house",
+        health="down",
+        health_detail="broker unreachable",
+    )
+
+    marked = {
+        node.id: node.issue for node in controller.brain_graph().nodes if node.issue
+    }
+    assert list(marked) == ["house.scale"]
+    assert "broker unreachable" in marked["house.scale"]
+
+
 def test_an_advisory_issue_leaves_the_graph_clean(controller: FlowController):
     controller.issues = [
         ValidationIssue(