refactor(runtime): add run DDD boundary skeleton

backend/packages/harness/deerflow/runtime/runs/execution/executor.py

@@ -0,0 +1,18 @@
+"""Run executor contract."""
+
+from __future__ import annotations
+
+from typing import Protocol
+
+from ..domain import Run
+
+
+class RunExecutor(Protocol):
+    """Executes one run against the underlying agent or graph runtime."""
+
+    async def execute(self, run: Run) -> None: ...
+
+
+__all__ = [
+    "RunExecutor",
+]