feat(cron): default isolated jobs to announce delivery and enhance scheduling options

- Updated isolated cron jobs to default to `announce` delivery mode, improving user experience.
- Enhanced scheduling options to accept ISO 8601 timestamps for `schedule.at`, while still supporting epoch milliseconds.
- Refined documentation to clarify delivery modes and scheduling formats.
- Adjusted related CLI commands and UI components to reflect these changes, ensuring consistency across the platform.
- Improved handling of legacy delivery fields for backward compatibility.

This update streamlines the configuration of isolated jobs, making it easier for users to manage job outputs and schedules.

ui/src/ui/app-defaults.ts

@@ -25,9 +25,9 @@ export const DEFAULT_CRON_FORM: CronFormState = {
   wakeMode: "next-heartbeat",
   payloadKind: "systemEvent",
   payloadText: "",
-  deliveryMode: "legacy",
+  deliveryMode: "announce",
   deliveryChannel: "last",
   deliveryTo: "",
   timeoutSeconds: "",
-  postToMainPrefix: "",
+  postToMainPrefix: "Cron",
 };

ui/src/ui/controllers/cron.ts

@@ -121,6 +121,7 @@ export async function addCronJob(state: CronState) {
             to: state.cronForm.deliveryTo.trim() || undefined,
           }
         : undefined;
+    const legacyPrefix = state.cronForm.postToMainPrefix.trim() || "Cron";
     const agentId = state.cronForm.agentId.trim();
     const job = {
       name: state.cronForm.name.trim(),
@@ -133,10 +134,8 @@ export async function addCronJob(state: CronState) {
       payload,
       delivery,
       isolation:
-        state.cronForm.postToMainPrefix.trim() &&
-        state.cronForm.sessionTarget === "isolated" &&
-        state.cronForm.deliveryMode === "legacy"
-          ? { postToMainPrefix: state.cronForm.postToMainPrefix.trim() }
+        state.cronForm.sessionTarget === "isolated" && state.cronForm.deliveryMode === "legacy"
+          ? { postToMainPrefix: legacyPrefix }
           : undefined,
     };
     if (!job.name) {

ui/src/ui/views/cron.ts

@@ -212,7 +212,7 @@ export function renderCron(props: CronProps) {
                         })}
                     >
                       <option value="legacy">Main summary (legacy)</option>
-                      <option value="announce">Announce summary</option>
+                      <option value="announce">Announce summary (default)</option>
                       <option value="deliver">Deliver full output</option>
                       <option value="none">None (internal)</option>
                     </select>