feat(cron): add 'at' parameter for one-time scheduled tasks

nanobot/agent/tools/cron.py

@@ -50,6 +50,10 @@ class CronTool(Tool):
                     "type": "string",
                     "description": "Cron expression like '0 9 * * *' (for scheduled tasks)"
                 },
+                "at": {
+                    "type": "string",
+                    "description": "ISO datetime for one-time execution (e.g. '2026-02-12T10:30:00')"
+                },
                 "job_id": {
                     "type": "string",
                     "description": "Job ID (for remove)"
@@ -64,30 +68,38 @@ class CronTool(Tool):
         message: str = "",
         every_seconds: int | None = None,
         cron_expr: str | None = None,
+        at: str | None = None,
         job_id: str | None = None,
         **kwargs: Any
     ) -> str:
         if action == "add":
-            return self._add_job(message, every_seconds, cron_expr)
+            return self._add_job(message, every_seconds, cron_expr, at)
         elif action == "list":
             return self._list_jobs()
         elif action == "remove":
             return self._remove_job(job_id)
         return f"Unknown action: {action}"
     
-    def _add_job(self, message: str, every_seconds: int | None, cron_expr: str | None) -> str:
+    def _add_job(self, message: str, every_seconds: int | None, cron_expr: str | None, at: str | None) -> str:
         if not message:
             return "Error: message is required for add"
         if not self._channel or not self._chat_id:
             return "Error: no session context (channel/chat_id)"
         
         # Build schedule
+        delete_after = False
         if every_seconds:
             schedule = CronSchedule(kind="every", every_ms=every_seconds * 1000)
         elif cron_expr:
             schedule = CronSchedule(kind="cron", expr=cron_expr)
+        elif at:
+            from datetime import datetime
+            dt = datetime.fromisoformat(at)
+            at_ms = int(dt.timestamp() * 1000)
+            schedule = CronSchedule(kind="at", at_ms=at_ms)
+            delete_after = True
         else:
-            return "Error: either every_seconds or cron_expr is required"
+            return "Error: either every_seconds, cron_expr, or at is required"
         
         job = self._cron.add_job(
             name=message[:30],
@@ -96,6 +108,7 @@ class CronTool(Tool):
             deliver=True,
             channel=self._channel,
             to=self._chat_id,
+            delete_after_run=delete_after,
         )
         return f"Created job '{job.name}' (id: {job.id})"