The Command inlined below, only has one variant that responds with Result, and thus rarely has a way to respond with errors.

/// Commands sent to the service by the operator.
pub enum Command {
    /// Announce repository references for given repository and namespaces to peers.
    AnnounceRefs(RepoId, HashSet<PublicKey>, chan::Sender<RefsAt>),
    /// Announce local repositories to peers.
    AnnounceInventory,
    /// Add repository to local inventory.
    AddInventory(RepoId, chan::Sender<bool>),
    /// Connect to node with the given address.
    Connect(NodeId, Address, ConnectOptions),
    /// Disconnect from node.
    Disconnect(NodeId),
    /// Get the node configuration.
    Config(chan::Sender<Config>),
    /// Get the node's listen addresses.
    ListenAddrs(chan::Sender<Vec<std::net::SocketAddr>>),
    /// Lookup seeds for the given repository in the routing table, and report
    /// sync status for given namespaces.
    Seeds(RepoId, HashSet<PublicKey>, chan::Sender<Seeds>),
    /// Fetch the given repository from the network.
    Fetch(RepoId, NodeId, time::Duration, chan::Sender<FetchResult>),
    /// Seed the given repository.
    Seed(RepoId, Scope, chan::Sender<bool>),
    /// Unseed the given repository.
    Unseed(RepoId, chan::Sender<bool>),
    /// Follow the given node.
    Follow(NodeId, Option<Alias>, chan::Sender<bool>),
    /// Unfollow the given node.
    Unfollow(NodeId, chan::Sender<bool>),
    /// Query the internal service state.
    QueryState(Arc<QueryState>, chan::Sender<Result<(), CommandError>>),
}

I believe this will always result in command socket timing out rather than reporting a useful error.

A better approach would be to be able to return an error, probably something akin to String for easy serialization. This can improve the situation with the control socket waiting for results that it never receives, and resulting in the opaque "socket timeout error".