diff --git a/backend/tests/test_workflow_api.py b/backend/tests/test_workflow_api.py
new file mode 100644
index 0000000..feb02d5
--- /dev/null
+++ b/backend/tests/test_workflow_api.py
@@ -0,0 +1,74 @@
+from pathlib import Path
+from types import SimpleNamespace
+import tempfile
+import unittest
+from unittest.mock import patch
+
+from sqlalchemy import create_engine
+from sqlalchemy.orm import sessionmaker
+
+from backend.agent import api
+from backend.agent.models import WorkflowDefinition, WorkflowRun
+from backend.agent.schemas import WorkflowRunRequest
+from backend.agent.workflows.builtins import seed_builtin_workflows
+from backend.database import Base
+from backend.models import ChatMessage, ChatSession
+
+
+class WorkflowApiTests(unittest.IsolatedAsyncioTestCase):
+    async def asyncSetUp(self):
+        self.temp = tempfile.TemporaryDirectory()
+        self.engine = create_engine(
+            f"sqlite:///{Path(self.temp.name) / 'api.db'}",
+            connect_args={"check_same_thread": False},
+        )
+        Base.metadata.create_all(self.engine)
+        self.Session = sessionmaker(bind=self.engine)
+        db = self.Session()
+        seed_builtin_workflows(db)
+        direct = db.query(WorkflowDefinition).filter_by(slug="input-output").one()
+        chat = ChatSession(session_id="regenerate-chat")
+        db.add(chat)
+        db.flush()
+        user = ChatMessage(session_pk=chat.id, role="user", content="original")
+        db.add(user)
+        db.flush()
+        db.add(ChatMessage(
+            session_pk=chat.id,
+            role="assistant",
+            content="old answer",
+            workflow_id=direct.id,
+            workflow_revision_id=direct.current_revision_id,
+        ))
+        db.commit()
+        self.user_message_id = user.message_id
+        self.direct_revision_id = direct.current_revision_id
+        db.close()
+
+    async def asyncTearDown(self):
+        self.engine.dispose()
+        self.temp.cleanup()
+
+    async def test_regeneration_reuses_user_row_and_prunes_old_answer(self):
+        started = []
+        fake_runtime = SimpleNamespace(start=started.append)
+        request = WorkflowRunRequest(
+            session_id="regenerate-chat",
+            message="edited",
+            model="test-model",
+            selection_mode="direct",
+            workflow_revision_id=self.direct_revision_id,
+            regenerate_index=0,
+        )
+        with patch.object(api, "SessionLocal", self.Session), patch.object(api, "runtime", fake_runtime):
+            response = await api.create_workflow_run(request)
+
+        self.assertEqual(started, [response["run_id"]])
+        db = self.Session()
+        rows = db.query(ChatMessage).order_by(ChatMessage.id.asc()).all()
+        self.assertEqual(len(rows), 1)
+        self.assertEqual(rows[0].message_id, self.user_message_id)
+        self.assertEqual(rows[0].content, "edited")
+        run = db.query(WorkflowRun).filter_by(id=response["run_id"]).one()
+        self.assertEqual(run.user_message_id, self.user_message_id)
+        db.close()
diff --git a/backend/tests/test_workflow_runtime.py b/backend/tests/test_workflow_runtime.py
index 0b88800..1b07309 100644
--- a/backend/tests/test_workflow_runtime.py
+++ b/backend/tests/test_workflow_runtime.py
@@ -98,6 +98,9 @@ class RuntimeTests(unittest.IsolatedAsyncioTestCase):
         self.assertTrue(db.query(WorkflowEvent).filter(WorkflowEvent.event_type == "source_found").count())
         db.close()
 
+        test_run = await self.execute(self.create_run(value, session=False))
+        self.assertEqual(test_run.status, "completed")
+
     async def test_concurrent_nodes_and_condition_branch(self):
         value = graph(
             [