A new workspace binary. It reads flysim's own configuration (same env file,
same FLY_FEED_BIND, FLY_BUS_DIR and idle cadence), subscribes to
fly.feed.snapshots as fly-edge with one latest slot and one delivery in
flight, turns each publication back into a Snapshot with feedbus::receive and
serves it through flysim's feed::router, so hello, wants, drop-oldest and the
2 Hz idle header are flysim's code and the bytes are flysim's bytes.
The port is bound only once the first snapshot has arrived, and when the bus
goes away every client is dropped and the port unbound, which is what a
stopped flysim looks like to the stage; then it reconnects every 500 ms.
FLY_EDGE_METRICS_ADDR serves /metrics (fly_frames_sent_total and
fly_feed_clients under their flysim names, plus fly_edge_*) and /healthz.
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