Review round 1. A bind failure after subscribing was logged once as
"waiting for the feed bus". session() now ends as Unreachable, BindFailed or
BusLost, each logged as what it is (once per streak), and
fly_edge_bind_failures_total counts the second; a new parity test holds the
port, sees the edge fail to bind without claiming to serve, frees it and gets
served.
feed.bus_dir (FLY_BUS_DIR) must be absolute and non-empty, checked in either
mode, since flysim and the edge each resolve it and a relative path would
let them disagree.
The sizing worst case was 7 stuck subscribers; that seat does not exist,
since edge.sock admits one client. It is that client with all 4
subscriptions it may open: 4*3+1+2 = 15 snapshots, about 1.8 MB. feedbus's
comment and unit test say so, and stall.rs's hoarding scenario now takes all
four subscriptions, checks a fifth and a second connection are refused, and
bounds the store at 15 snapshots.
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.
