Python: Include sub-workflow structure in graph signature for checkpoint validation

python/packages/core/agent_framework/_workflows/_workflow.py

@@ -744,10 +744,19 @@ def _compute_graph_signature(self) -> dict[str, Any]:
         ignoring data/state changes. Used to verify that a workflow's structure hasn't
         changed when resuming from checkpoints.
         """
-        executors_signature = {
-            executor_id: f"{executor.__class__.__module__}.{executor.__class__.__name__}"
-            for executor_id, executor in self.executors.items()
-        }
+        from ._workflow_executor import WorkflowExecutor
+
+        executors_signature = {}
+        for executor_id, executor in self.executors.items():
+            executor_sig: Any = f"{executor.__class__.__module__}.{executor.__class__.__name__}"
+
+            if isinstance(executor, WorkflowExecutor):
+                executor_sig = {
+                    "type": executor_sig,
+                    "sub_workflow": executor.workflow._graph_signature,
+                }
+
+            executors_signature[executor_id] = executor_sig
 
         edge_groups_signature: list[dict[str, Any]] = []
         for group in self.edge_groups:

python/packages/core/tests/workflow/test_checkpoint_validation.py

@@ -7,6 +7,7 @@
     WorkflowBuilder,
     WorkflowCheckpointException,
     WorkflowContext,
+    WorkflowExecutor,
     WorkflowRunState,
     handler,
 )
@@ -81,3 +82,87 @@ async def test_resume_succeeds_when_graph_matches() -> None:
     ]
 
     assert any(event.type == "status" and event.state == WorkflowRunState.IDLE for event in events)
+
+
+# -- Sub-workflow checkpoint validation tests --
+
+
+class SubStartExecutor(Executor):
+    @handler
+    async def run(self, message: str, ctx: WorkflowContext[str]) -> None:
+        await ctx.send_message(message)
+
+
+class SubFinishExecutor(Executor):
+    @handler
+    async def finish(self, message: str, ctx: WorkflowContext[Never, str]) -> None:
+        await ctx.yield_output(message)
+
+
+def build_sub_workflow(sub_finish_id: str = "sub_finish"):
+    sub_start = SubStartExecutor(id="sub_start")
+    sub_finish = SubFinishExecutor(id=sub_finish_id)
+    return WorkflowBuilder(start_executor=sub_start).add_edge(sub_start, sub_finish).build()
+
+
+def build_parent_workflow(storage: InMemoryCheckpointStorage, sub_finish_id: str = "sub_finish"):
+    sub_workflow = build_sub_workflow(sub_finish_id=sub_finish_id)
+    sub_executor = WorkflowExecutor(sub_workflow, id="sub_wf", allow_direct_output=True)
+
+    start = StartExecutor(id="start")
+    finish = FinishExecutor(id="finish")
+
+    builder = (
+        WorkflowBuilder(max_iterations=3, start_executor=start, checkpoint_storage=storage)
+        .add_edge(start, sub_executor)
+        .add_edge(sub_executor, finish)
+    )
+    return builder.build()
+
+
+async def test_resume_succeeds_when_sub_workflow_matches() -> None:
+    storage = InMemoryCheckpointStorage()
+    workflow = build_parent_workflow(storage, sub_finish_id="sub_finish")
+
+    _ = [event async for event in workflow.run("hello", stream=True)]
+
+    checkpoints = await storage.list_checkpoints()
+    assert checkpoints, "expected at least one checkpoint to be created"
+    target_checkpoint = checkpoints[-1]
+
+    resumed_workflow = build_parent_workflow(storage, sub_finish_id="sub_finish")
+
+    events = [
+        event
+        async for event in resumed_workflow.run(
+            checkpoint_id=target_checkpoint.checkpoint_id,
+            checkpoint_storage=storage,
+            stream=True,
+        )
+    ]
+
+    assert any(event.type == "status" and event.state == WorkflowRunState.IDLE for event in events)
+
+
+async def test_resume_fails_when_sub_workflow_changes() -> None:
+    storage = InMemoryCheckpointStorage()
+    workflow = build_parent_workflow(storage, sub_finish_id="sub_finish")
+
+    _ = [event async for event in workflow.run("hello", stream=True)]
+
+    checkpoints = await storage.list_checkpoints()
+    assert checkpoints, "expected at least one checkpoint to be created"
+    target_checkpoint = checkpoints[-1]
+
+    # Build parent with a structurally different sub-workflow (different executor id inside)
+    mismatched_workflow = build_parent_workflow(storage, sub_finish_id="sub_finish_alt")
+
+    with pytest.raises(WorkflowCheckpointException, match="Workflow graph has changed"):
+        _ = [
+            event
+            async for event in mismatched_workflow.run(
+                checkpoint_id=target_checkpoint.checkpoint_id,
+                checkpoint_storage=storage,
+                stream=True,
+            )
+        ]