fix(runtime): make rollback restore checkpoint supersede newer checkpoints (#2582)

* Restore rollback checkpoints with fresh ids

* Tighten rollback checkpoint tests and imports

* Update test_run_worker_rollback.py

---------

Co-authored-by: Willem Jiang <willem.jiang@gmail.com>

backend/packages/harness/deerflow/runtime/runs/worker.py

@@ -23,6 +23,8 @@ from dataclasses import dataclass, field
 from functools import lru_cache
 from typing import TYPE_CHECKING, Any, Literal, cast
 
+from langgraph.checkpoint.base import empty_checkpoint
+
 if TYPE_CHECKING:
     from langchain_core.messages import HumanMessage
 
@@ -442,6 +444,12 @@ async def _rollback_to_pre_run_checkpoint(
     if checkpoint_to_restore.get("id") is None:
         logger.warning("Run %s rollback skipped: pre-run checkpoint has no checkpoint id", run_id)
         return
+    restore_marker = _new_checkpoint_marker()
+    checkpoint_to_restore = {
+        **checkpoint_to_restore,
+        "id": restore_marker["id"],
+        "ts": restore_marker["ts"],
+    }
     metadata = pre_run_snapshot.get("metadata", {})
     metadata_to_restore = metadata if isinstance(metadata, dict) else {}
     raw_checkpoint_ns = pre_run_snapshot.get("checkpoint_ns")
@@ -493,6 +501,11 @@ async def _rollback_to_pre_run_checkpoint(
         )
 
 
+def _new_checkpoint_marker() -> dict[str, str]:
+    marker = empty_checkpoint()
+    return {"id": marker["id"], "ts": marker["ts"]}
+
+
 def _lg_mode_to_sse_event(mode: str) -> str:
     """Map LangGraph internal stream_mode name to SSE event name.