NewRunner returns a runner, implementing the agent's jobRunner interface.

Umask is a wrapper for `unix.Umask()` on non-Windows platforms.

RunStateInterrupt means the job is cancelled or should be terminated for some other reason.

RunStateStart means the job can begin.

RunStateWait means the job is not ready to start executing yet.

Empty is an empty RPC message.

ExitCode is an RPC message that specifies an exit status for a client ID.

Logs is an RPC message that contains log data.

RegisterResponse is an RPC message to registering clients containing info needed to run.

Runner implements the agent's jobRunner interface, but instead of directly managing a subprocess, it runs a socket server that is connected to from another container.

RunState is an RPC message that describes to a client whether the job should continue waiting before running, start running, or stop running.