AssertionError: Invalid app mode: agent

Start in api/core/memory/token_buffer_memory.py at _build_prompt_message_with_files, then trace the suggested-questions request through api/services/message_service.py and api/controllers/web/message.py. Reproduce the GET /api/messages/{id}/suggested-questions failure for a conversation whose mode is agent, and verify that the request no longer raises AssertionError or returns a 500.

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Dify version

1.17.1

Cloud or Self Hosted

Self Hosted (Docker)

Steps to reproduce

2026-09-16 06:00:47.779 ERROR [Dummy-1119] [message.py:265] 44638e7c1e425f05bd1acc755e9c74ff - internal server error.
Traceback (most recent call last):
File "/app/api/controllers/web/message.py", line 242, in get
questions = MessageService.get_suggested_questions_after_answer(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/app/api/services/message_service.py", line 426, in get_suggested_questions_after_answer
histories = memory.get_history_prompt_text(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/app/api/core/memory/token_buffer_memory.py", line 243, in get_history_prompt_text
prompt_messages = self.get_history_prompt_messages(max_token_limit=max_token_limit, message_limit=message_limit)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/app/api/core/memory/token_buffer_memory.py", line 189, in get_history_prompt_messages
user_prompt_message = self._build_prompt_message_with_files(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/app/api/core/memory/token_buffer_memory.py", line 86, in _build_prompt_message_with_files
raise AssertionError(f"Invalid app mode: {self.conversation.mode}")
AssertionError: Invalid app mode: agent
2026-09-16 06:00:47.780 ERROR [Dummy-1119] [app.py:875] 44638e7c1e425f05bd1acc755e9c74ff - Exception on /api/messages/dda45706-a869-4ee6-a013-7f6526a03dd0/suggested-questions [GET]
Traceback (most recent call last):
File "/app/api/controllers/web/message.py", line 242, in get
questions = MessageService.get_suggested_questions_after_answer(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/app/api/services/message_service.py", line 426, in get_suggested_questions_after_answer
histories = memory.get_history_prompt_text(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/app/api/core/memory/token_buffer_memory.py", line 243, in get_history_prompt_text
prompt_messages = self.get_history_prompt_messages(max_token_limit=max_token_limit, message_limit=message_limit)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/app/api/core/memory/token_buffer_memory.py", line 189, in get_history_prompt_messages
user_prompt_message = self._build_prompt_message_with_files(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/app/api/core/memory/token_buffer_memory.py", line 86, in _build_prompt_message_with_files
raise AssertionError(f"Invalid app mode: {self.conversation.mode}")
AssertionError: Invalid app mode: agent

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/app/api/.venv/lib/python3.12/site-packages/flask/app.py", line 917, in full_dispatch_request
rv = self.dispatch_request()
^^^^^^^^^^^^^^^^^^^^^^^
File "/app/api/.venv/lib/python3.12/site-packages/flask/app.py", line 902, in dispatch_request
return self.ensure_sync(self.view_functions[rule.endpoint])(**view_args) # type: ignore[no-any-return]
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/app/api/.venv/lib/python3.12/site-packages/flask_restx/api.py", line 404, in wrapper
resp = resource(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^
File "/app/api/.venv/lib/python3.12/site-packages/flask/views.py", line 110, in view
return current_app.ensure_sync(self.dispatch_request)(**kwargs) # type: ignore[no-any-return]
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/app/api/.venv/lib/python3.12/site-packages/flask_restx/resource.py", line 41, in dispatch_request
resp = meth(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^
File "/app/api/controllers/web/wraps.py", line 38, in decorated
return view(app_model, end_user, *args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/app/api/controllers/web/message.py", line 266, in get
raise InternalServerError()
werkzeug.exceptions.InternalServerError: 500 Internal Server Error: The server encountered an internal error and was unable to complete your request. Either the server is overloaded or there is an error in the application.
2026-09-16 06:00:48.685 INFO [Dummy-1120] [_client.py:1025] c1bdbd4995a851b7801963bcecc1168c - HTTP Request: POST http://plugin_daemon:5002/plugin/81dee897-d63d-4dc7-8072-6f7fb3338da3/dispatch/llm/invoke "HTTP/1.1 200 OK"

✔️ Expected Behavior

❌ Actual Behavior

No response