Function emit_estart 

pub fn emit_estart(
    ws_port: u16,
    web_port: u16,
    version: &str,
    build_time: &str,
    instance_id: &str,
)

Step 6: Emit AGENTMUXSRV-ESTART on stderr (exact format from cmd/server/main-server.go:617) pending_migrations reflects any migrations that failed during the in-process run above. Non-zero causes the status-bar to show a “Migration failed — restart to retry” message. Zero is the expected steady-state.