feat(cron): configurable failure alerts for repeated job errors (openclaw#24789) thanks @0xbrak

Verified:
- pnpm install --frozen-lockfile
- pnpm check
- pnpm test -- --run src/cron/service.failure-alert.test.ts src/cli/cron-cli.test.ts src/gateway/protocol/cron-validators.test.ts

Co-authored-by: 0xbrak <181251288+0xbrak@users.noreply.github.com>
Co-authored-by: Tak Hoffman <781889+Takhoffman@users.noreply.github.com>

src/cron/types.ts

@@ -56,6 +56,13 @@ export type CronRunOutcome = {
   sessionKey?: string;
 };
 
+export type CronFailureAlert = {
+  after?: number;
+  channel?: CronMessageChannel;
+  to?: string;
+  cooldownMs?: number;
+};
+
 export type CronPayload =
   | { kind: "systemEvent"; text: string }
   | {
@@ -102,6 +109,8 @@ export type CronJobState = {
   lastDurationMs?: number;
   /** Number of consecutive execution errors (reset on success). Used for backoff. */
   consecutiveErrors?: number;
+  /** Last failure alert timestamp (ms since epoch) for cooldown gating. */
+  lastFailureAlertAtMs?: number;
   /** Number of consecutive schedule computation errors. Auto-disables job after threshold. */
   scheduleErrorCount?: number;
   /** Explicit delivery outcome, separate from execution outcome. */
@@ -128,6 +137,7 @@ export type CronJob = {
   wakeMode: CronWakeMode;
   payload: CronPayload;
   delivery?: CronDelivery;
+  failureAlert?: CronFailureAlert | false;
   state: CronJobState;
 };