fix(cron): initialize MCP servers before constructing the cron AIAgent (#21354)

cron/scheduler.py:run_job() constructed AIAgent(...) without ever calling
discover_mcp_tools(). The CLI and gateway paths do this at startup; cron
jobs inherited none of it and the user's configured mcp_servers were
invisible inside every cron run.

Insert discover_mcp_tools() right before AIAgent(), wrapped in try/except
so a broken MCP server can't kill an otherwise-working cron job. The call
is idempotent: register_mcp_servers() short-circuits on already-connected
servers, so subsequent ticks in the same scheduler process pay ~0ms.
Scoped to the LLM path only; no_agent script jobs skip it entirely.

Closes #4219.

tests/cron/test_scheduler_mcp_init.py

@@ -0,0 +1,140 @@
+"""Regression tests for MCP server availability in cron jobs.
+
+Background
+==========
+``cron/scheduler.py:run_job()`` constructs ``AIAgent(...)`` directly without
+calling ``discover_mcp_tools()`` — the initialization that CLI and gateway
+paths do at startup. Cron jobs therefore never saw any MCP tools from
+``mcp_servers`` in config.yaml. See #4219.
+
+The fix inserts ``discover_mcp_tools()`` before the ``AIAgent(...)`` call,
+wrapped in try/except so a broken MCP server can't kill an otherwise
+working cron job. ``discover_mcp_tools`` is idempotent — subsequent ticks
+short-circuit on already-connected servers.
+"""
+
+from __future__ import annotations
+
+from unittest.mock import patch, MagicMock
+
+import pytest
+
+
+def test_run_job_calls_discover_mcp_tools_before_agent_construction():
+    """The LLM-path branch of run_job must call discover_mcp_tools() before
+    the AIAgent construction, so MCP tools are in the registry by the time
+    the agent asks for its tool schema."""
+    from cron import scheduler
+
+    job = {
+        "id": "mcp-cron-test",
+        "name": "mcp-cron-test",
+        "prompt": "test",
+    }
+
+    call_order = []
+
+    def fake_discover():
+        call_order.append("discover_mcp_tools")
+        return ["mcp_server1_tool"]
+
+    # AIAgent is a class; replace with a recording stub
+    class _FakeAgent:
+        def __init__(self, *args, **kwargs):
+            call_order.append("AIAgent.__init__")
+            self._kwargs = kwargs
+            self._interrupt_requested = False
+            self.quiet_mode = True
+
+        def run_conversation(self, *args, **kwargs):
+            return {
+                "final_response": "ok",
+                "messages": [],
+            }
+
+    with patch("tools.mcp_tool.discover_mcp_tools", side_effect=fake_discover), \
+         patch("run_agent.AIAgent", _FakeAgent), \
+         patch("cron.scheduler._resolve_cron_enabled_toolsets", return_value=None):
+        scheduler.run_job(job)
+
+    # Discovery must be called, and must be called BEFORE agent construction.
+    assert "discover_mcp_tools" in call_order, (
+        "run_job did not call discover_mcp_tools — MCP tools unavailable in cron"
+    )
+    d_idx = call_order.index("discover_mcp_tools")
+    a_idx = call_order.index("AIAgent.__init__")
+    assert d_idx < a_idx, (
+        f"discover_mcp_tools was called AFTER AIAgent construction "
+        f"(indices discover={d_idx}, agent={a_idx}); MCP tools missed the "
+        f"registry window. Full order: {call_order}"
+    )
+
+
+def test_run_job_tolerates_discover_mcp_tools_failure():
+    """A broken MCP server must not kill an otherwise working cron job.
+    discover_mcp_tools() raising should be caught and logged, and the agent
+    should still run."""
+    from cron import scheduler
+
+    job = {
+        "id": "mcp-cron-fail",
+        "name": "mcp-cron-fail",
+        "prompt": "test",
+    }
+
+    agent_was_constructed = []
+
+    class _FakeAgent:
+        def __init__(self, *args, **kwargs):
+            agent_was_constructed.append(True)
+            self._interrupt_requested = False
+            self.quiet_mode = True
+
+        def run_conversation(self, *args, **kwargs):
+            return {"final_response": "ok", "messages": []}
+
+    def fake_discover_that_raises():
+        raise RuntimeError("MCP server unreachable")
+
+    with patch(
+        "tools.mcp_tool.discover_mcp_tools",
+        side_effect=fake_discover_that_raises,
+    ), patch("run_agent.AIAgent", _FakeAgent), \
+         patch("cron.scheduler._resolve_cron_enabled_toolsets", return_value=None):
+        # Should NOT raise
+        success, doc, final_response, error = scheduler.run_job(job)
+
+    assert agent_was_constructed, (
+        "AIAgent was not constructed after discover_mcp_tools raised — "
+        "MCP failure incorrectly killed the cron job"
+    )
+
+
+def test_no_agent_cron_job_does_not_initialize_mcp():
+    """Cron jobs with no_agent=True are script-only — no AIAgent, no MCP
+    tools needed. We must NOT pay the MCP init cost for those."""
+    from cron import scheduler
+
+    job = {
+        "id": "noagent-job",
+        "name": "noagent-job",
+        "no_agent": True,
+        "script": "/nonexistent/script.sh",
+    }
+
+    discover_called = []
+
+    def fake_discover():
+        discover_called.append(True)
+        return []
+
+    # _run_job_script returns (ok, output); make it fail cleanly so we
+    # don't need a real script file.
+    with patch("tools.mcp_tool.discover_mcp_tools", side_effect=fake_discover), \
+         patch("cron.scheduler._run_job_script", return_value=(False, "no such file")):
+        scheduler.run_job(job)
+
+    assert not discover_called, (
+        "discover_mcp_tools was called for a no_agent job — wasted MCP init "
+        "for a script-only cron tick"
+    )