doEvent.fireSense_spreadFit.Rdinit schedules spreadFitPrepare, and, unless the ledger already holds a fit for this polygon
(or refitExisting is TRUE), estimateThreshold then run (or debug when mode has "debug").
When heldOutFold is 1 or 2, init instead schedules only spreadFitPrepare,
estimateThreshold and crossValidate (that one fold): never run, so the full fit and the
ledger write never happen.
doEvent.fireSense_spreadFit(sim, eventTime, eventType, debug = FALSE)the simList, invisibly.