Follow-up to the failure_deliver salvage (#100375):
- _preflight_check_delivery also checks the failure lane, so a typo'd
failure_deliver platform blocks at config-validation time instead of
surfacing only when a failure occurs — exactly when the notice must
not be lost. Duplicate lanes are checked once.
- The dashboard cron-update normalizer treats failure_deliver like
deliver (text normalization; empty clears the optional override
instead of coalescing), closing the one update path that could write
an unnormalized value into jobs.json.
4 guard tests; both fixes mutation-checked (neutralize -> red, restore -> green).
95f62ca3bf