Before this change, `fastCopy` created a cancellable context for the sync and
stored its cancel func on the `bisyncRun`, but only ever called it when
gracefully shutting down. On a normal run, it was never called, and until it is
cancelled, a context from `context.WithCancel` stays registered with its nearest
cancellable ancestor.
For an rc job, that ancestor is the job's own context, which the job registry
retains for `--rc-job-expire-duration`. The sync context carries bisync's
`LoggerOpt`, whose `LoggerFn` is a method value on `*bisyncRun`, so a finished
run was kept alive -- including the Path1 and Path2 listings -- for as long as the
job was.
This change fixes the issue by cancelling the sync context when `fastCopy`
returns. The cancel func is still stored on the `bisyncRun`, so a graceful
shutdown can still interrupt a sync that is in progress.
nielash
387b4b5e11