phase 1 of #784 (unix-domain agent web UI for #14 prerequisite).
backwards-compatible: when HIVE_WEB_SOCKET is set + non-empty, bind a
UnixListener at that path instead of the legacy TCP bind on HIVE_PORT.
empty env var treated as unset so a stray HIVE_WEB_SOCKET= doesn't
trap an un-bindable empty path.
bind_unix helper:
- mkdir -p the socket parent (covers first-boot fresh /run/hive-agent/
bind-mount target)
- best-effort unlink of stale socket (clean exit removes it, crash
leaves it; bind(2) refuses to overwrite)
- mode 0o660 so gateway peers in the same unix group can connect (the
bind-mount source dir ACL is the real gate; perms are defence in
depth)
axum 0.8's Listener trait covers tokio::net::UnixListener directly
(no extra feature/dep required).
next phases (separate PRs):
- step 2: c0re bind-mounts /run/hive-agent/ + writes agent-sockets.json
alongside agent-ports.json
- step 3: gateway proxy_pass http://unix:… (atlas)
- step 4: drop TCP bind once gateway no longer needs it
0ef79b8032