diff --git a/nanobot/agent/tools/cron.py b/nanobot/agent/tools/cron.py
index fe1dce6..13b1e12 100644
--- a/nanobot/agent/tools/cron.py
+++ b/nanobot/agent/tools/cron.py
@@ -1,5 +1,6 @@
 """Cron tool for scheduling reminders and tasks."""
 
+from contextvars import ContextVar
 from typing import Any
 
 from nanobot.agent.tools.base import Tool
@@ -14,12 +15,21 @@ class CronTool(Tool):
         self._cron = cron_service
         self._channel = ""
         self._chat_id = ""
+        self._in_cron_context: ContextVar[bool] = ContextVar("cron_in_context", default=False)
 
     def set_context(self, channel: str, chat_id: str) -> None:
         """Set the current session context for delivery."""
         self._channel = channel
         self._chat_id = chat_id
 
+    def set_cron_context(self, active: bool):
+        """Mark whether the tool is executing inside a cron job callback."""
+        return self._in_cron_context.set(active)
+
+    def reset_cron_context(self, token) -> None:
+        """Restore previous cron context."""
+        self._in_cron_context.reset(token)
+
     @property
     def name(self) -> str:
         return "cron"
@@ -72,6 +82,8 @@ class CronTool(Tool):
         **kwargs: Any,
     ) -> str:
         if action == "add":
+            if self._in_cron_context.get():
+                return "Error: cannot schedule new jobs from within a cron job execution"
             return self._add_job(message, every_seconds, cron_expr, tz, at)
         elif action == "list":
             return self._list_jobs()
diff --git a/nanobot/cli/commands.py b/nanobot/cli/commands.py
index 2662e9f..f9fe347 100644
--- a/nanobot/cli/commands.py
+++ b/nanobot/cli/commands.py
@@ -296,6 +296,7 @@ def gateway(
     # Set cron callback (needs agent)
     async def on_cron_job(job: CronJob) -> str | None:
         """Execute a cron job through the agent."""
+        from nanobot.agent.tools.cron import CronTool
         from nanobot.agent.tools.message import MessageTool
         reminder_note = (
             "[Scheduled Task] Timer finished.\n\n"
@@ -303,12 +304,21 @@ def gateway(
             f"Scheduled instruction: {job.payload.message}"
         )
 
-        response = await agent.process_direct(
-            reminder_note,
-            session_key=f"cron:{job.id}",
-            channel=job.payload.channel or "cli",
-            chat_id=job.payload.to or "direct",
-        )
+        # Prevent the agent from scheduling new cron jobs during execution
+        cron_tool = agent.tools.get("cron")
+        cron_token = None
+        if isinstance(cron_tool, CronTool):
+            cron_token = cron_tool.set_cron_context(True)
+        try:
+            response = await agent.process_direct(
+                reminder_note,
+                session_key=f"cron:{job.id}",
+                channel=job.payload.channel or "cli",
+                chat_id=job.payload.to or "direct",
+            )
+        finally:
+            if isinstance(cron_tool, CronTool) and cron_token is not None:
+                cron_tool.reset_cron_context(cron_token)
 
         message_tool = agent.tools.get("message")
         if isinstance(message_tool, MessageTool) and message_tool._sent_in_turn: