Sync listener address is hardcoded (0.0.0.0:9090); bind failure is non-fatal so a second instance runs silently without sync #209

Summary

The sync WebSocket listener address is hardcoded to SyncListenerConfig::default() = 0.0.0.0:9090 — no config key, no env override. Combined with the bind failure being non-fatal, a second NodeDB instance on the same host starts cleanly, logs one WARN, and runs silently without sync.

Worse: because the first instance holds 0.0.0.0:9090, any client (or readiness probe) pointed at 127.0.0.1:9090 for the second instance silently connects to the first instance instead — a test/staging replica can end up syncing into production.

Environment

nodedb v0.4.0 (tag 38bfc3084). Every other listener (pgwire/native/http) is configurable via [server.ports]; sync is the only one that isn't.

Mechanism

• nodedb/src/bootstrap/listeners.rs:152 — let sync_config = SyncListenerConfig::default(); (nothing read from ServerConfig)
• nodedb/src/control/server/sync/listener.rs:34 — default 0.0.0.0:9090
• bootstrap/listeners.rs — bind failure logs sync listener failed to start (non-fatal) and boot continues

Observed live: a 0.4.0 test instance coexisting with a production instance ran for two days sync-less with only the one WARN line to show for it; TCP probes on 127.0.0.1:9090 kept "succeeding" against the wrong instance.

Suggested fix

Read the sync listen address from config like every other listener (e.g. [server.ports] sync = 9090 or a [sync] listen_addr), and consider making bind failure fatal-by-default (or at least surfaced in readiness), since a sync-Origin that cannot accept sync is usually misconfigured rather than degraded.

Minimal interim patch we're running locally (env override, mirrors the pre-0.4.0 behavior our tooling relied on):

// bootstrap/listeners.rs
let mut sync_config = crate::control::server::sync::listener::SyncListenerConfig::default();
if let Ok(addr) = std::env::var("NODEDB_SYNC_LISTEN_ADDR") {
    match addr.parse() {
        Ok(parsed) => sync_config.listen_addr = parsed,
        Err(e) => tracing::warn!(error = %e, addr = %addr,
            "invalid NODEDB_SYNC_LISTEN_ADDR; keeping default sync listen address"),
    }
}

Happy to PR either shape (config key preferred) after triage.