Function handle_command 

pub(super) fn handle_command(
    cmd: Command,
    client: &mut Client<JournaledSession>,
    outbound: &mut PacketWriter<GrowBuffer>,
    pending: &mut Pending,
    max_packet_size: Option<u32>,
    outbound_aliases: &mut OutboundAliases,
    queued_waiting: &mut Vec<Sender<Result<(), Error>>>,
)

Handles a single user command on a live connection.

Operation-level failures (capabilities, packet-id exhaustion, un-encodable properties, oversized payload) resolve only that operation’s future; they never end the connection.