fix(cron): support tz parameter with at for one-time scheduled tasks

The tz parameter was previously only allowed with cron_expr. When users
specified tz with at for one-time tasks, it returned an error. Now tz
works with both cron_expr and at — naive ISO datetimes are interpreted
in the given timezone via ZoneInfo.

- Relax validation: allow tz with cron_expr or at
- Apply ZoneInfo to naive datetimes in the at branch
- Update SKILL.md with at+tz examples
- Add automated tests for tz+at combinations

Co-authored-by: weitongtong <tongtong.wei@nodeskai.com>
Made-with: Cursor

nanobot/agent/tools/cron.py

@@ -60,7 +60,7 @@ class CronTool(Tool):
                 },
                 "tz": {
                     "type": "string",
-                    "description": "IANA timezone for cron expressions (e.g. 'America/Vancouver')",
+                    "description": "IANA timezone for cron_expr or at (e.g. 'America/Vancouver')",
                 },
                 "at": {
                     "type": "string",
@@ -104,8 +104,8 @@ class CronTool(Tool):
             return "Error: message is required for add"
         if not self._channel or not self._chat_id:
             return "Error: no session context (channel/chat_id)"
-        if tz and not cron_expr:
-            return "Error: tz can only be used with cron_expr"
+        if tz and not cron_expr and not at:
+            return "Error: tz can only be used with cron_expr or at"
         if tz:
             from zoneinfo import ZoneInfo
 
@@ -127,6 +127,8 @@ class CronTool(Tool):
                 dt = datetime.fromisoformat(at)
             except ValueError:
                 return f"Error: invalid ISO datetime format '{at}'. Expected format: YYYY-MM-DDTHH:MM:SS"
+            if tz and dt.tzinfo is None:
+                dt = dt.replace(tzinfo=ZoneInfo(tz))
             at_ms = int(dt.timestamp() * 1000)
             schedule = CronSchedule(kind="at", at_ms=at_ms)
             delete_after = True

nanobot/skills/cron/SKILL.md

@@ -30,6 +30,11 @@ One-time scheduled task (compute ISO datetime from current time):
 cron(action="add", message="Remind me about the meeting", at="<ISO datetime>")
 ```
 
+One-time task with timezone (naive datetime interpreted in given tz):
+```
+cron(action="add", message="Drink water!", at="2026-03-18T14:40:00", tz="Asia/Shanghai")
+```
+
 Timezone-aware cron:
 ```
 cron(action="add", message="Morning standup", cron_expr="0 9 * * 1-5", tz="America/Vancouver")
@@ -51,7 +56,8 @@ cron(action="remove", job_id="abc123")
 | weekdays at 5pm | cron_expr: "0 17 * * 1-5" |
 | 9am Vancouver time daily | cron_expr: "0 9 * * *", tz: "America/Vancouver" |
 | at a specific time | at: ISO datetime string (compute from current time) |
+| at 2pm Shanghai time | at: "2026-03-18T14:00:00", tz: "Asia/Shanghai" |
 
 ## Timezone
 
-Use `tz` with `cron_expr` to schedule in a specific IANA timezone. Without `tz`, the server's local timezone is used.
+Use `tz` with `cron_expr` or `at` to schedule in a specific IANA timezone. Without `tz`, the server's local timezone is used.

tests/test_cron_tool_tz_at.py

@@ -0,0 +1,103 @@
+"""Tests for CronTool at+tz timezone handling."""
+
+from datetime import datetime, timezone
+from zoneinfo import ZoneInfo
+
+import pytest
+
+from nanobot.agent.tools.cron import CronTool
+from nanobot.cron.service import CronService
+
+
+def _make_tool(tmp_path) -> CronTool:
+    service = CronService(tmp_path / "cron" / "jobs.json")
+    tool = CronTool(service)
+    tool.set_context("test-channel", "test-chat")
+    return tool
+
+
+@pytest.mark.asyncio
+async def test_at_with_tz_naive_datetime(tmp_path) -> None:
+    """Naive datetime + tz should be interpreted in the given timezone."""
+    tool = _make_tool(tmp_path)
+    result = await tool.execute(
+        action="add",
+        message="Shanghai reminder",
+        at="2026-03-18T14:00:00",
+        tz="Asia/Shanghai",
+    )
+    assert "Created job" in result
+
+    jobs = tool._cron.list_jobs()
+    assert len(jobs) == 1
+    # Asia/Shanghai is UTC+8, so 14:00 Shanghai = 06:00 UTC
+    expected_dt = datetime(2026, 3, 18, 14, 0, 0, tzinfo=ZoneInfo("Asia/Shanghai"))
+    expected_ms = int(expected_dt.timestamp() * 1000)
+    assert jobs[0].schedule.at_ms == expected_ms
+
+
+@pytest.mark.asyncio
+async def test_at_with_tz_aware_datetime_preserves_original(tmp_path) -> None:
+    """Datetime that already has tzinfo should not be overridden by tz param."""
+    tool = _make_tool(tmp_path)
+    # Pass an aware datetime (UTC) with a different tz param
+    result = await tool.execute(
+        action="add",
+        message="UTC reminder",
+        at="2026-03-18T06:00:00+00:00",
+        tz="Asia/Shanghai",
+    )
+    assert "Created job" in result
+
+    jobs = tool._cron.list_jobs()
+    assert len(jobs) == 1
+    # The +00:00 offset should be preserved (dt.tzinfo is not None, so tz is ignored)
+    expected_dt = datetime(2026, 3, 18, 6, 0, 0, tzinfo=timezone.utc)
+    expected_ms = int(expected_dt.timestamp() * 1000)
+    assert jobs[0].schedule.at_ms == expected_ms
+
+
+@pytest.mark.asyncio
+async def test_tz_without_cron_or_at_fails(tmp_path) -> None:
+    """Passing tz without cron_expr or at should return an error."""
+    tool = _make_tool(tmp_path)
+    result = await tool.execute(
+        action="add",
+        message="Bad config",
+        tz="America/Vancouver",
+    )
+    assert "Error" in result
+    assert "tz can only be used with cron_expr or at" in result
+
+
+@pytest.mark.asyncio
+async def test_at_without_tz_unchanged(tmp_path) -> None:
+    """Naive datetime without tz should use system-local interpretation (existing behavior)."""
+    tool = _make_tool(tmp_path)
+    result = await tool.execute(
+        action="add",
+        message="Local reminder",
+        at="2026-03-18T14:00:00",
+    )
+    assert "Created job" in result
+
+    jobs = tool._cron.list_jobs()
+    assert len(jobs) == 1
+    # fromisoformat without tz → system local; just verify job was created
+    local_dt = datetime.fromisoformat("2026-03-18T14:00:00")
+    expected_ms = int(local_dt.timestamp() * 1000)
+    assert jobs[0].schedule.at_ms == expected_ms
+
+
+@pytest.mark.asyncio
+async def test_at_with_invalid_tz_fails(tmp_path) -> None:
+    """Invalid timezone should return an error."""
+    tool = _make_tool(tmp_path)
+    result = await tool.execute(
+        action="add",
+        message="Bad tz",
+        at="2026-03-18T14:00:00",
+        tz="Invalid/Timezone",
+    )
+    assert "Error" in result
+    assert "unknown timezone" in result