feat(scheduler): run fixed-time tasks in a chosen time zone#23911

@@ -145,7 +145,7 @@ const ListScheduledTasksTool = Tool.make("list_scheduled_tasks", {
 
 const UpdateScheduledTaskTool = Tool.make("update_scheduled_task", {
   description:
-    "Update an existing scheduled task by scheduledTaskId (from list_scheduled_tasks). Webhook schedule dedupe accepts replayKey, coalesceKey, and coalesceWindowSeconds (10–3600, default 120) to suppress replays for 7 days and retain the latest payload in each fixed window. Only the provided fields change; omit a field to leave it as-is. Use enabled=false to pause a task without deleting it. Set bindToCurrentThread to move the task between posting into this thread and launching a fresh thread per run. A webhook schedule without filters keeps the stored filters; pass filters to replace them, or filters:[] to clear them.",
+    "Update an existing scheduled task by scheduledTaskId (from list_scheduled_tasks). Webhook schedule dedupe accepts replayKey, coalesceKey, and coalesceWindowSeconds (10–3600, default 120) to suppress replays for 7 days and retain the latest payload in each fixed window. Only the provided fields change; omit a field to leave it as-is. The same holds inside schedule: an optional field such as timeZone that you leave out keeps its stored value, and null removes it. Use enabled=false to pause a task without deleting it. Set bindToCurrentThread to move the task between posting into this thread and launching a fresh thread per run. A webhook schedule without filters keeps the stored filters; pass filters to replace them, or filters:[] to clear them.",

@@ -145,7 +145,7 @@ const ListScheduledTasksTool = Tool.make("list_scheduled_tasks", {
 
 const UpdateScheduledTaskTool = Tool.make("update_scheduled_task", {
   description:
-    "Update an existing scheduled task by scheduledTaskId (from list_scheduled_tasks). Webhook schedule dedupe accepts replayKey, coalesceKey, and coalesceWindowSeconds (10–3600, default 120) to suppress replays for 7 days and retain the latest payload in each fixed window. Only the provided fields change; omit a field to leave it as-is. Use enabled=false to pause a task without deleting it. Set bindToCurrentThread to move the task between posting into this thread and launching a fresh thread per run. A webhook schedule without filters keeps the stored filters; pass filters to replace them, or filters:[] to clear them.",
+    "Update an existing scheduled task by scheduledTaskId (from list_scheduled_tasks). Webhook schedule dedupe accepts replayKey, coalesceKey, and coalesceWindowSeconds (10–3600, default 120) to suppress replays for 7 days and retain the latest payload in each fixed window. Only the provided fields change; omit a field to leave it as-is. The same holds inside schedule: an optional field such as timeZone that you leave out keeps its stored value, and null removes it. Use enabled=false to pause a task without deleting it. Set bindToCurrentThread to move the task between posting into this thread and launching a fresh thread per run. A webhook schedule without filters keeps the stored filters; pass filters to replace them, or filters:[] to clear them.",

@@ -168,7 +173,9 @@ export function scheduleFromDraft(draft: ScheduleDraft): ScheduledTaskUpsertSche
     return minutes >= 1 && Number.isSafeInteger(everyMs) ? { type: "interval", everyMs } : null;
   }
   const weekdays = [...new Set(draft.weekdays)].sort((a, b) => a - b);
+  const timeZone = parseTimeZoneDraft(draft.timeZone);
   if (
+    timeZone === undefined ||

@@ -76,6 +77,13 @@ Webhook tasks only run when their URL is called, so they can't be run
 immediately.
 Leaving an edited form asks before discarding unsaved changes.
 
+## Scheduled task timing
+
+A task that runs **At a time** uses the environment's clock unless you set a
+**Time zone**, such as `America/Chicago`. It then keeps that local time when
+daylight saving starts or ends. A time skipped when clocks move forward runs
+an hour later that day, and a time that repeats when they move back runs once.