Constant CONNECT_TIMEOUT 

pub const CONNECT_TIMEOUT: Duration;

Default bounded connect timeout for outbound cast/send TCP connections.

Without a bound, TcpStream::connect uses the OS default connect timeout (tens of seconds to minutes), so an omni cast / send / devices to an unreachable device or relay hangs. This mirrors the bounded connect the omni doctor --probe path already uses (probe_tcp in lib.rs), applied to the real cast/send paths. 5s fails fast versus the OS default while still tolerating a slow tailnet handshake.