feat(cron): add failure destination support to failed cron jobs (#31059)

* feat(cron): add failure destination support with webhook mode and bestEffort handling

Extends PR #24789 failure alerts with features from PR #29145:
- Add webhook delivery mode for failure alerts (mode: 'webhook')
- Add accountId support for multi-account channel configurations
- Add bestEffort handling to skip alerts when job has bestEffort=true
- Add separate failureDestination config (global + per-job in delivery)
- Add duplicate prevention (prevents sending to same as primary delivery)
- Add CLI flags: --failure-alert-mode, --failure-alert-account-id
- Add UI fields for new options in web cron editor

* fix(cron): merge failureAlert mode/accountId and preserve failureDestination on updates

- Fix mergeCronFailureAlert to merge mode and accountId fields
- Fix mergeCronDelivery to preserve failureDestination on updates
- Fix isSameDeliveryTarget to use 'announce' as default instead of 'none'
  to properly detect duplicates when delivery.mode is undefined

* fix(cron): validate webhook mode requires URL in resolveFailureDestination

When mode is 'webhook' but no 'to' URL is provided, return null
instead of creating an invalid plan that silently fails later.

* fix(cron): fail closed on webhook mode without URL and make failureDestination fields clearable

- sendCronFailureAlert: fail closed when mode is webhook but URL is missing
- mergeCronDelivery: use per-key presence checks so callers can clear
  nested failureDestination fields via cron.update

Note: protocol:check shows missing internalEvents in Swift models - this is
a pre-existing issue unrelated to these changes (upstream sync needed).

* fix(cron): use separate schema for failureDestination and fix type cast

- Create CronFailureDestinationSchema excluding after/cooldownMs fields
- Fix type cast in sendFailureNotificationAnnounce to use CronMessageChannel

* fix(cron): merge global failureDestination with partial job overrides

When job has partial failureDestination config, fall back to global
config for unset fields instead of treating it as a full override.

* fix(cron): avoid forcing announce mode and clear inherited to on mode change

- UI: only include mode in patch if explicitly set to non-default
- delivery.ts: clear inherited 'to' when job overrides mode, since URL
  semantics differ between announce and webhook modes

* fix(cron): preserve explicit to on mode override and always include mode in UI patches

- delivery.ts: preserve job-level explicit 'to' when overriding mode
- UI: always include mode in failureAlert patch so users can switch between announce/webhook

* fix(cron): allow clearing accountId and treat undefined global mode as announce

- UI: always include accountId in patch so users can clear it
- delivery.ts: treat undefined global mode as announce when comparing for clearing inherited 'to'

* Cron: harden failure destination routing and add regression coverage

* Cron: resolve failure destination review feedback

* Cron: drop unrelated timeout assertions from conflict resolution

* Cron: format cron CLI regression test

* Cron: align gateway cron test mock types

---------

Co-authored-by: Tak Hoffman <781889+Takhoffman@users.noreply.github.com>

src/cli/cron-cli/register.cron-edit.ts

@@ -73,6 +73,11 @@ export function registerCronEditCommand(cron: Command) {
       )
       .option("--failure-alert-to <dest>", "Failure alert destination")
       .option("--failure-alert-cooldown <duration>", "Minimum time between alerts (e.g. 1h, 30m)")
+      .option("--failure-alert-mode <mode>", "Failure alert delivery mode (announce or webhook)")
+      .option(
+        "--failure-alert-account-id <id>",
+        "Account ID for failure alert channel (multi-account setups)",
+      )
       .action(async (id, opts) => {
         try {
           if (opts.session === "main" && opts.message) {
@@ -286,11 +291,15 @@ export function registerCronEditCommand(cron: Command) {
           const hasFailureAlertChannel = typeof opts.failureAlertChannel === "string";
           const hasFailureAlertTo = typeof opts.failureAlertTo === "string";
           const hasFailureAlertCooldown = typeof opts.failureAlertCooldown === "string";
+          const hasFailureAlertMode = typeof opts.failureAlertMode === "string";
+          const hasFailureAlertAccountId = typeof opts.failureAlertAccountId === "string";
           const hasFailureAlertFields =
             hasFailureAlertAfter ||
             hasFailureAlertChannel ||
             hasFailureAlertTo ||
-            hasFailureAlertCooldown;
+            hasFailureAlertCooldown ||
+            hasFailureAlertMode ||
+            hasFailureAlertAccountId;
           const failureAlertFlag =
             typeof opts.failureAlert === "boolean" ? opts.failureAlert : undefined;
           if (failureAlertFlag === false && hasFailureAlertFields) {
@@ -322,6 +331,17 @@ export function registerCronEditCommand(cron: Command) {
               }
               failureAlert.cooldownMs = cooldownMs;
             }
+            if (hasFailureAlertMode) {
+              const mode = String(opts.failureAlertMode).trim().toLowerCase();
+              if (mode !== "announce" && mode !== "webhook") {
+                throw new Error("Invalid --failure-alert-mode (must be 'announce' or 'webhook').");
+              }
+              failureAlert.mode = mode;
+            }
+            if (hasFailureAlertAccountId) {
+              const accountId = String(opts.failureAlertAccountId).trim();
+              failureAlert.accountId = accountId ? accountId : undefined;
+            }
             patch.failureAlert = failureAlert;
           }