refactor(schedule): move orchestrator to application/ + review fixes (stage 8)

Follow-up to the layered refactor (review-driven):

- Move scheduling/orchestrator.py -> application/orchestrator.py
  (orchestrator is application-level coordination, not a cron-trigger
  primitive; matches the intended target tree)
- Migrate orchestrator re-exports from scheduling/__init__.py to
  application/__init__.py; scheduling/ now exposes only CronScheduler
- Rewrite imports + 5 mock.patch string targets in test_janitor.py and
  the orchestrator import in test_layering.py
- Update docstring refs in application/service.py + execution/worker.py
- Add 4 runner smoke tests (test_layering.py): _limited_log under-limit /
  empty-sentinel / above-MAX_LOG_BYTES truncation; execute_artifact
  rejects unsupported script_type with ValueError
- infrastructure/__init__.py re-exports SchedulerStorageClient so
  ``from schedule.infrastructure import SchedulerStorageClient`` is a
  stable top-level surface
- CLAUDE.md engineering note: extend the commit trail to 7476c27 and
  note the stage-8 orchestrator placement

Zero behavior change; schedule/pyproject.toml untouched. 29 tests green.

Co-Authored-By: Claude <noreply@anthropic.com>

schedule/tests/test_layering.py

@@ -36,7 +36,7 @@ from schedule.domain.context import (
 from schedule.domain.execution import ExecutionResult
 from schedule.execution import NodeExecutor
 from schedule.infrastructure.storage import SchedulerStorageClient
-from schedule.scheduling.orchestrator import DispatchOrchestrator
+from schedule.application.orchestrator import DispatchOrchestrator
 from schedule.scheduling.scheduler import CronScheduler
 
 
@@ -175,3 +175,48 @@ def test_notebook_runner_shim_reexports_real_main() -> None:
     from schedule.notebook_runner import main as shim_main
 
     assert shim_main is real.main
+
+
+# ── execution/runners: stage-4 merge boundary smoke (F4) ──────────────────
+
+
+def test_limited_log_under_limit_returns_encoded_unchanged() -> None:
+    from schedule.execution.runners import notebook
+
+    assert notebook._limited_log("hello") == b"hello"
+
+
+def test_limited_log_empty_returns_sentinel() -> None:
+    from schedule.execution.runners import notebook
+
+    assert notebook._limited_log("") == b"execution produced no console output\n"
+
+
+def test_limited_log_above_max_bytes_truncates_with_suffix() -> None:
+    from schedule.execution.runners import notebook
+
+    sentinel = b"\n[log truncated by scheduler worker]\n"
+    overflowing = "x" * (notebook.MAX_LOG_BYTES + 1)
+    truncated = notebook._limited_log(overflowing)
+    assert len(truncated) == notebook.MAX_LOG_BYTES
+    assert truncated.endswith(sentinel)
+
+
+@pytest.mark.asyncio
+async def test_execute_artifact_unsupported_script_type_raises() -> None:
+    """``script_type`` outside ``{"notebook", "python"}`` must raise —
+    otherwise the worker would silently drop a malformed run into the
+    queue and the node would hang.
+    """
+    from schedule.execution.runners import notebook
+
+    with pytest.raises(ValueError, match="unsupported script_type"):
+        await notebook.execute_artifact(
+            source=b"print('hi')\n",
+            run_id="01RUN0000000000000000000A",
+            node_run_id="01NODE000000000000000000A",
+            script_type="bogus",
+            artifact_path="x.py",
+            arguments=[],
+            timeout_seconds=30,
+        )