fix(cron): accept list-form deliver values so deliver=['telegram'] works (#17456)

The cron schema contracts deliver as a string ("local", "origin",
"telegram", "telegram:chat_id[:thread_id]", or comma-separated combos),
but MCP clients and scripts sometimes pass an array like ['telegram'].

Before this change, the list was written to jobs.json verbatim, and
the scheduler's str(deliver).split(',') then tried to resolve the
literal string "['telegram']" as a platform — returning None and
logging 'no delivery target resolved for deliver=[\'telegram\']'.

Fix on both ends:
- tools/cronjob_tools.py: normalize deliver at the API boundary on
  create and update, so storage is always a string.
- cron/scheduler.py: normalize deliver in _resolve_delivery_targets,
  so existing jobs.json entries with list-form deliver are handled
  gracefully without requiring users to edit the file.

Closes #17139

tests/cron/test_scheduler.py

@@ -279,6 +279,44 @@ class TestResolveDeliveryTarget:
             "thread_id": None,
         }
 
+    def test_list_form_deliver_is_normalized(self, monkeypatch):
+        """deliver=['telegram'] (Python list) should resolve like 'telegram' string.
+
+        Regression test for #17139: MCP clients / scripts that pass the deliver
+        field as an array-shaped value used to fail with "no delivery target
+        resolved for deliver=['telegram']" because ``str(['telegram'])`` was
+        passed through to ``split(',')`` verbatim.
+        """
+        monkeypatch.setenv("TELEGRAM_HOME_CHANNEL", "-4004")
+        job = {
+            "deliver": ["telegram"],
+            "origin": None,
+        }
+
+        assert _resolve_delivery_target(job) == {
+            "platform": "telegram",
+            "chat_id": "-4004",
+            "thread_id": None,
+        }
+
+    def test_list_form_multiple_platforms_normalized(self, monkeypatch):
+        """deliver=['telegram', 'discord'] resolves to multiple targets."""
+        from cron.scheduler import _resolve_delivery_targets
+
+        monkeypatch.setenv("TELEGRAM_HOME_CHANNEL", "-111")
+        monkeypatch.setenv("DISCORD_HOME_CHANNEL", "-222")
+        job = {"deliver": ["telegram", "discord"], "origin": None}
+
+        targets = _resolve_delivery_targets(job)
+        platforms = sorted(t["platform"] for t in targets)
+        assert platforms == ["discord", "telegram"]
+
+    def test_empty_list_form_deliver_resolves_to_local(self):
+        """deliver=[] is treated as local (no delivery)."""
+        from cron.scheduler import _resolve_delivery_targets
+
+        assert _resolve_delivery_targets({"deliver": []}) == []
+
 
 class TestDeliverResultWrapping:
     """Verify that cron deliveries are wrapped with header/footer and no longer mirrored."""

tests/tools/test_cronjob_tools.py

@@ -231,3 +231,60 @@ class TestUnifiedCronjobTool:
         assert updated["success"] is True
         assert updated["job"]["skills"] == []
         assert updated["job"]["skill"] is None
+
+    def test_create_normalizes_list_form_deliver(self):
+        """deliver=['telegram'] (list) is stored as the string 'telegram'.
+
+        Regression for #17139: MCP clients / scripts sometimes pass ``deliver``
+        as an array.  Prior to the fix, ``['telegram']`` was written verbatim
+        to ``jobs.json`` and the scheduler then tried to resolve the literal
+        string ``"['telegram']"`` as a platform, failing with
+        "no delivery target resolved".
+        """
+        from cron.jobs import get_job
+
+        created = json.loads(
+            cronjob(
+                action="create",
+                prompt="Daily briefing",
+                schedule="every 1h",
+                deliver=["telegram"],
+            )
+        )
+        assert created["success"] is True
+        stored = get_job(created["job_id"])
+        assert stored["deliver"] == "telegram"
+
+    def test_create_normalizes_multi_element_list_deliver(self):
+        """deliver=['telegram', 'discord'] is stored as 'telegram,discord'."""
+        from cron.jobs import get_job
+
+        created = json.loads(
+            cronjob(
+                action="create",
+                prompt="Daily briefing",
+                schedule="every 1h",
+                deliver=["telegram", "discord"],
+            )
+        )
+        assert created["success"] is True
+        stored = get_job(created["job_id"])
+        assert stored["deliver"] == "telegram,discord"
+
+    def test_update_normalizes_list_form_deliver(self):
+        """update with deliver=['telegram'] stores the canonical string."""
+        from cron.jobs import get_job
+
+        created = json.loads(
+            cronjob(action="create", prompt="x", schedule="every 1h")
+        )
+        updated = json.loads(
+            cronjob(
+                action="update",
+                job_id=created["job_id"],
+                deliver=["telegram"],
+            )
+        )
+        assert updated["success"] is True
+        stored = get_job(created["job_id"])
+        assert stored["deliver"] == "telegram"