Coatue FR (Frank Long): jobs delivering into shared channels publish
engine failure notices ('⚠️ Cron X failed…') to those channels with no
opt-out. Adds an optional per-job failure_deliver field sharing
deliver's grammar: on failure, targets resolve from failure_deliver
when set (local = structural silence; state still recorded in
last_status/last_error/run history). Success delivery is unchanged;
absent field = today's behavior byte-for-byte.
Honored by every failure-category engine notice: the run_job failure
summary (+streak nudge), the escaped-failure retry path, drift-skip and
blocked-config alerts (composed into the same delivery), and the
gateway-shutdown interrupted-run notice (_notify_interrupted_cron_jobs).
Surfaces: cronjob tool create/update (same bot-chat validation as
deliver; '' clears on update), hermes cron create/edit
--failure-deliver, docs tip in automate-with-cron.
Existing fake_deliver test doubles gained **kwargs for the new
for_failure keyword — signature-compat only, no behavior change.
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