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.
A second bus subscriber folds executions, errors, timings and queue lag
into per-minute rollups, keeps failures with their traceback and an audit
trail of who published what, and records one row per cascade — manual runs
and previews included, under an id of their own that writes no idempotency
markers. Read back through /observability/*, which always answers 200 so a
degraded engine still renders its own health screen.
Also fixes two things found on the way: node-health alerts read `status`
where the engine publishes `health`, so a device dropping never alerted
anyone, and the Redis queue reported `parked: 0` whatever was held.
stroblme