@@ -1,5 +1,5 @@
 {
   "claudeSystemAppendBytes": 5129,
   "codexAdditionalContextBytes": 6859,
-  "mcpToolListJsonBytes": 46191
+  "mcpToolListJsonBytes": 46163
 }
@@ -67,7 +67,7 @@ const OrchestratorMcpSchedule = Schema.Union([
   OrchestratorMcpScheduleFromJsonString,
 ]).annotate({
   description:
-    "Trigger: {type:'interval',everyMs}, {type:'fixed_time',timeOfDay,weekdays?} daily, {type:'once',runAt} for one date and time, or {type:'webhook'}.",
+    "Trigger: {type:'interval',everyMs}, {type:'fixed_time',timeOfDay,weekdays?}, {type:'once',runAt}, or {type:'webhook'}.",
 });
 
 const OrchestratorMcpTargetOptionsFromRecord = Schema.Record(
 
@@ -22,6 +22,15 @@ describe("ScheduledTaskSchedule", () => {
       everyMs: MIN_SCHEDULED_TASK_INTERVAL_MS - 1,
     });
   });
+
+  it("accepts a one-time run only with an offset", () => {
+    for (const runAt of ["2026-11-03T09:00Z", "2026-11-03T09:00:00.000-08:00"]) {
+      expect(decodeUpsertSchedule({ type: "once", runAt })).toEqual({ type: "once", runAt });
+    }
+    for (const runAt of ["2026-11-03T09:00", "2026-13-03T09:00Z", "tomorrow"]) {
+      expect(() => decodeUpsertSchedule({ type: "once", runAt })).toThrow();
+    }
+  });
 });
 
 it.each(["literal", " ", "\t\n", "{{body.bad", "{{unknown.field}}"])(
 
@@ -45,16 +45,18 @@ const ScheduledTaskFixedTimeSchedule = Schema.Struct({
   ),
 });
 
+const ISO_WITH_OFFSET = /^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}(:\d{2}(\.\d+)?)?(Z|[+-]\d{2}:\d{2})$/;
+
+// Checked by filter, not pattern, to keep the MCP tool schema small.
 const ScheduledTaskOnceSchedule = Schema.Struct({
   type: Schema.Literal("once"),
   runAt: TrimmedNonEmptyString.check(
-    Schema.isPattern(/^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}(:\d{2}(\.\d+)?)?(Z|[+-]\d{2}:\d{2})$/),
-    Schema.makeFilter((value) => Number.isFinite(Date.parse(value)) || "Invalid date."),
-  ).annotate({
-    description: "ISO 8601 date and time with an offset, such as 2026-11-02T15:00:00-08:00.",
-  }),
-}).annotate({
-  description: "Run once at this time. If the server is offline then, it runs when back.",
+    Schema.makeFilter(
+      (value) =>
+        (ISO_WITH_OFFSET.test(value) && Number.isFinite(Date.parse(value))) ||
+        "Expected an ISO date and time with an offset.",
+    ),
+  ),
 });
 
 const ScheduledTaskWebhookSignatureFields = {
Original file line number	Diff line number	Diff line change
`@@ -1,5 +1,5 @@`
`1`	`1`	`{`
`2`	`2`	`"claudeSystemAppendBytes": 5129,`
`3`	`3`	`"codexAdditionalContextBytes": 6859,`
`4`		`- "mcpToolListJsonBytes": 46191`
	`4`	`+ "mcpToolListJsonBytes": 46163`
`5`	`5`	`}`