Logs are streamed for each running pipeline on a websocket at /logs/{pipelineID}. engine.TailStep demuxes stdout and stderr from the container's logs and pipes that out to corresponding stdout and stderr channels. These channels are maintained inside engine's container struct, key'd by the pipeline ID, and protected by a read/write mutex. engine.LogChannels fetches the stdout/stderr chans as recieve-only if the pipeline is known to exist. Signed-off-by: Anirudh Oppiliappan <anirudh@tangled.sh>