The runner's runner log session is the channel: the server watches the build row every two seconds while the session is open and ends it with exit 3 when the build is no longer running. The runner reads exit 3 alone as "stop", kills the step, and returns; any other end is still a lost stream. A late runner done on a cancelled build is a no-op.
e2e: a real runner sitting in sleep 120 stops within seconds of build cancel, the log names who cancelled it, and the row stays cancelled after the runner's report.
Wiki: Parity note and user guide updated, pushed with the merge.
Ref #90