Even with --api-addr set, mycelium also opens an internal JSON-RPC
endpoint on 127.0.0.1:8990 by default (visible in --debug as
\"Starting JSON-RPC server listen_addr=127.0.0.1:8990\"). When a
previous run left an orphan mycelium running as root — which we
can't SIGKILL from a user-level Child::kill_on_drop — the new
instance fails to bind 8990 and exits ~10s after startup, with no
sidecar://exited event because the kill never landed.
Pin --metrics-api-address to a fresh ephemeral port alongside the
other three. Known limitation: stopping the daemon still doesn't
reliably kill the root child; the user has to `sudo pkill mycelium`
between runs. Will be addressed by an elevated-shutdown hook.
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