Take the engine off the path node code imports from, and let it stop

The worker script is handed to the interpreter by path, so app/flow was
sys.path[0] for every node: `import queue` got the engine's. It now drops
its own directory before anything else imports, and runs with the
deployment's credentials scrubbed out of its environment.

Also: reload builds off the event loop, the pool wakes what is blocked on
it when it stops, a refused metrics flush is kept for the next one rather
than dropped, and the cascade events are paired through failures.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017MeiWk3Yq12n2pTvnQWYvt

frontend/src/routes/_layout/health.tsx

@@ -185,7 +185,11 @@ function Health() {
   // Something just went wrong on the socket. The row for it is written on the
   // collector's next flush, so the refetch waits that out rather than asking
   // for a failure the database does not have yet.
-  const seen = live.length
+  //
+  // The newest event's minute, not the count: the count stops changing once the
+  // ring is full, and a per-event key would let a flapping node restart the
+  // timer forever without it ever firing.
+  const seen = live.length ? Math.floor(live[live.length - 1].ts / 60) : 0
   useEffect(() => {
     if (!seen) return
     const timer = setTimeout(() => {