Worker panes started by experimentTmux() / tmuxRunNextWorker() evaluate
the user's global.R inside a fresh scenario environment (not .GlobalEnv).
When the source call errors, the package captures sys.calls() and stashes
it on that scenario env so a post-mortem traceback is still possible without
polluting the user's global state. Use this accessor to retrieve it.
lastTraceback()A list of calls (as from sys.calls()) suitable for passing to
base::traceback(); NULL if no error has been captured in the current
session.
if (FALSE) { # \dontrun{
# After a worker pane errors:
traceback(SpaDES.project::lastTraceback())
} # }