Surface a failing connector poll as node health and a flow issue

The poll loop remembered what it read rather than what it published, so a
value the node could not publish counted as said: the next poll skipped it,
succeeded, and health went back to ok with the port still dark. Remember it
only after inject returns, and report ok last.

A node reporting itself down is now derived into its flow's issues on read
and counted on the health summary, so the canvas marks it and Home says so.
Being down does not stop the flow, and the issue clears by itself when the
node reports well again. The repeating poll warning is logged once per
outage rather than once per tick.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01K1moruzue2kTJd3uVisgNk

docs/interface/flow-editor.md

@@ -146,9 +146,12 @@ The canvas validates as you edit and marks the node each issue belongs to:
 - a node reading a message it also writes, with nothing to start it from
 - code that did not load
 - a webhook with no shared secret (advisory — it does not stop the flow)
+- a node that loaded but reports itself down, such as a connector that cannot
+  reach its device
 
-A flow with any of these except the last does not run, and the health summary
-on Home counts it.
+A flow with any of these except the last two does not run, and the health
+summary on Home counts it. The last one clears on its own once the node reports
+itself well again.
 
 ## See also