fix(scheduler): ensure scheduler starts after setup/config update

Add ensure_started() to SchedulerService as idempotent entry point.
Start scheduler in auth setup run_initialization() after NFO scan.
Sync anime_directory and start scheduler in config update endpoint.
Add unit and endpoint tests for ensure_started() behavior.

tests/api/test_config_endpoints.py

@@ -2,7 +2,7 @@
 
 import tempfile
 from pathlib import Path
-from unittest.mock import patch
+from unittest.mock import AsyncMock, patch
 
 import pytest
 from httpx import ASGITransport, AsyncClient
@@ -207,3 +207,46 @@ async def test_tmdb_validation_endpoint_exists(authenticated_client):
     assert "message" in data
     assert data["valid"] is False  # Empty key should be invalid
     assert "required" in data["message"].lower()
+
+
+@pytest.mark.asyncio
+async def test_update_config_with_anime_directory_starts_scheduler(
+    authenticated_client, mock_config_service
+):
+    """PUT /api/config with anime_directory syncs and starts scheduler."""
+    mock_scheduler = AsyncMock()
+    
+    with patch("src.server.services.scheduler_service.get_scheduler_service") as mock_sched_fn:
+        mock_sched_fn.return_value = mock_scheduler
+
+        with patch("src.config.settings.settings") as mock_settings:
+            mock_settings.anime_directory = None
+
+            resp = await authenticated_client.put(
+                "/api/config",
+                json={"other": {"anime_directory": "/data/anime"}},
+            )
+
+            assert resp.status_code == 200
+            mock_scheduler.ensure_started.assert_called_once()
+
+
+@pytest.mark.asyncio
+async def test_update_config_without_anime_directory_does_not_start_scheduler(
+    authenticated_client, mock_config_service
+):
+    """PUT /api/config without new anime_directory does not call scheduler.ensure_started()."""
+    mock_scheduler = AsyncMock()
+    
+    with patch("src.server.services.scheduler_service.get_scheduler_service") as mock_sched_fn:
+        mock_sched_fn.return_value = mock_scheduler
+
+        with patch("src.config.settings.settings") as mock_settings:
+            mock_settings.anime_directory = "/already/set"
+
+            resp = await authenticated_client.put(
+                "/api/config", json={"other": {}}
+            )
+
+            assert resp.status_code == 200
+            mock_scheduler.ensure_started.assert_not_called()

tests/unit/test_scheduler_service.py

@@ -559,3 +559,38 @@ class TestStartupRecovery:
                 info_calls = [str(c) for c in mock_logger.info.call_args_list]
                 assert any("next_run" in c for c in info_calls)
 
+
+# ---------------------------------------------------------------------------
+# 12.8  ensure_started() – idempotent startup
+# ---------------------------------------------------------------------------
+
+class TestEnsureStarted:
+    @pytest.mark.asyncio
+    async def test_ensure_started_when_not_running(
+        self, scheduler_service, mock_config_service
+    ):
+        """ensure_started() calls start() when scheduler is not running."""
+        # Mock start method
+        scheduler_service.start = AsyncMock()
+
+        # Call ensure_started
+        await scheduler_service.ensure_started()
+
+        # Verify start() was called exactly once
+        scheduler_service.start.assert_called_once()
+
+    @pytest.mark.asyncio
+    async def test_ensure_started_when_already_running(self, scheduler_service):
+        """ensure_started() returns immediately when already running (idempotent)."""
+        # Set up as already running
+        scheduler_service._is_running = True
+
+        # Mock start method
+        scheduler_service.start = AsyncMock()
+
+        # Call ensure_started
+        await scheduler_service.ensure_started()
+
+        # Verify start() was NOT called
+        scheduler_service.start.assert_not_called()
+