fix(cron): drop top-level oneOf so OpenAI Codex/Responses accept tool schema

PR #3125 added a top-level `oneOf` branch to `_CRON_PARAMETERS` to
advertise per-action required fields. OpenAI Codex/Responses rejects
`oneOf`/`anyOf`/`allOf`/`enum`/`not` at the root of function
parameters, so any agent that registers the cron tool now fails to
start with:

    HTTP 400: Invalid schema for function 'cron': schema must have
    type 'object' and not have 'oneOf'/'anyOf'/'allOf'/'enum'/'not'
    at the top level.

Remove the top-level `oneOf`. The original intent of #3125 (stop LLMs
from looping on the #3113 contract mismatch) is preserved by:

  - `validate_params` — runtime-enforces `message` for `action='add'`
    and `job_id` for `action='remove'`
  - field descriptions — each schema field already flags
    "REQUIRED when action='...'" so the LLM sees the contract

The regression test is updated to lock the invariant in the other
direction: the top-level schema must not contain
`oneOf`/`anyOf`/`allOf`/`not`, and the REQUIRED hints must stay on
`message` and `job_id`.

Verified:
  - tests/cron/              70 passed
  - tests/agent/test_loop_cron_timezone.py + tests/providers/  232 passed

Co-authored-by: factory-droid[bot] <138933559+factory-droid[bot]@users.noreply.github.com>

nanobot/agent/tools/cron.py

@@ -43,30 +43,12 @@ _CRON_PARAMETERS = tool_parameters_schema(
     required=["action"],
     description=(
         "Action-specific parameters: add requires a non-empty message plus one schedule "
-        "(every_seconds, cron_expr, or at); remove requires job_id; list only needs action."
+        "(every_seconds, cron_expr, or at); remove requires job_id; list only needs action. "
+        "Per-action requirements are enforced at runtime (see field descriptions) so the "
+        "top-level schema stays compatible with providers (e.g. OpenAI Codex/Responses) that "
+        "reject oneOf/anyOf/allOf/enum/not at the root of function parameters."
     ),
 )
-_CRON_PARAMETERS["oneOf"] = [
-    {
-        "properties": {
-            "action": {"enum": ["add"]},
-            "message": {"type": "string", "minLength": 1},
-        },
-        "required": ["action", "message"],
-    },
-    {
-        "properties": {
-            "action": {"enum": ["list"]},
-        },
-        "required": ["action"],
-    },
-    {
-        "properties": {
-            "action": {"enum": ["remove"]},
-        },
-        "required": ["action", "job_id"],
-    },
-]
 
 
 @tool_parameters(_CRON_PARAMETERS)

tests/cron/test_cron_tool_list.py

@@ -348,24 +348,20 @@ def test_add_job_can_disable_delivery(tmp_path) -> None:
 def test_cron_schema_advertises_action_specific_requirements(tmp_path) -> None:
     tool = _make_tool(tmp_path)
 
+    # Only ``action`` is required at the schema root — per-action requirements
+    # are enforced at runtime via ``validate_params`` and surfaced to the LLM
+    # through field descriptions. We intentionally do NOT set top-level
+    # ``oneOf``/``anyOf``/``allOf``/``enum``/``not``: OpenAI Codex/Responses
+    # reject those at the root of function parameters (#3265 regression).
     assert tool.parameters["required"] == ["action"]
-    assert tool.parameters["oneOf"] == [
-        {
-            "properties": {
-                "action": {"enum": ["add"]},
-                "message": {"type": "string", "minLength": 1},
-            },
-            "required": ["action", "message"],
-        },
-        {
-            "properties": {"action": {"enum": ["list"]}},
-            "required": ["action"],
-        },
-        {
-            "properties": {"action": {"enum": ["remove"]}},
-            "required": ["action", "job_id"],
-        },
-    ]
+    for disallowed in ("oneOf", "anyOf", "allOf", "not"):
+        assert disallowed not in tool.parameters, (
+            f"Top-level '{disallowed}' is rejected by OpenAI Codex/Responses tool schemas"
+        )
+    message_desc = tool.parameters["properties"]["message"]["description"]
+    assert "REQUIRED" in message_desc and "action='add'" in message_desc
+    job_id_desc = tool.parameters["properties"]["job_id"]["description"]
+    assert "REQUIRED" in job_id_desc and "action='remove'" in job_id_desc
 
 
 def test_validate_params_requires_message_only_for_add(tmp_path) -> None: