Health: a flow that cannot run says so, and the brain marks which neurons

A dependency loop is flagged on the canvas and was invisible everywhere else:
/observability/summary answered "ok" with an empty problems list while the
published flow could not run at all. It now reports the flows validation
blocks, and the brain graph carries the reason on each neuron the issue names
so the view built to find broken wiring can show it.

Node errors stay counted once, as the nodes that failed to load, and an
advisory like an unauthenticated webhook marks nothing — it is worth saying,
but the flow still runs.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XC2jX6Hdj7pxGGKzBTrbqB

backend/app/api/routes/observability.py

@@ -17,7 +17,7 @@ from sqlalchemy import func
 from sqlmodel import col, select
 
 from app.api.deps import FlowControllerDep, SessionDep, get_current_user
-from app.flow.controller import NodeStatus
+from app.flow.controller import ADVISORY_ISSUES, NodeStatus
 from app.models import EngineEvent, FlowRun, MetricBucket
 
 router = APIRouter(
@@ -128,6 +128,22 @@ async def read_summary(
     if errored:
         problems.append(f"{len(errored)} node(s) failed to load")
 
+    # What the canvas flags on a flow — a dependency loop, an input nothing
+    # feeds — stops that flow running just as surely as a node that will not
+    # load, and until now this screen was the one place it did not show.
+    # `node_error` is left out: those are the nodes already counted above.
+    invalid = sorted(
+        {
+            issue.flow
+            for issue in controller.issues
+            if issue.flow
+            and issue.code != "node_error"
+            and issue.code not in ADVISORY_ISSUES
+        }
+    )
+    if invalid:
+        problems.append(f"{len(invalid)} flow(s) cannot run: {', '.join(invalid)}")
+
     statement = (
         select(func.count())
         .select_from(EngineEvent)
@@ -146,6 +162,7 @@ async def read_summary(
             ),
             "paused": len(paused),
             "quarantined": len(quarantined),
+            "invalid": len(invalid),
         },
         nodes={"total": len(entries), "error": len(errored)},
         queue=queue,