Run Flow component returns empty content when invoked as an Agent tool

Bug Description

When a Run Flow component is invoked by an Agent as a tool, the tool receives the correct input argument but returns empty content.

The same Run Flow component works correctly when executed directly without tool mode.

A similar problem was reported in #14791. I added my reproduction details there, but because that issue is already closed and the problem remains reproducible on Langflow 1.12.1, I am opening this issue to document the current behaviour.

This may also be related to the tool-invocation problem addressed by #14793.

Reproduction

Minimal setup Subflow

Chat Input → Chat Output

I also tested:

Text Input → Chat Output

The subflow only passes the received input directly to the output. It does not contain an Agent or language model.

Parent flow

Chat Input → Agent → Chat Output

The Run Flow component is connected to the Agent as a tool.

The Agent is instructed to call the Run Flow tool and pass its received input unchanged.

Steps to reproduce

1. Create a subflow containing only Chat Input → Chat Output.
2. Create a parent flow with an Agent.
3. Select the subflow in a Run Flow component.
4. Connect the Run Flow component to the Agent as a tool.
5. Send Test123 to the parent flow.
6. Inspect the Agent trace and Run Flow tool result.

Expected behavior

The Run Flow tool should pass Test123 to the subflow and return:

Test123

When I execute the Run Flow component directly and provide Test123 as its input, the subflow correctly returns Test123.

When the Agent invokes the same component as a tool, the tool-call arguments contain the correct value:

{
  "flow_tweak_data": {
    "TextInput-XXXX~input_value": "Test123"
  }
}

However, the tool returns empty content:

{
  "type": "tool_end",
  "output": {
    "content": ""
  }
}

Who can help?

@italojohnny @ogabrielluiz

Operating System

Linux Docker container on Windows 11

Langflow Version

1.12.1

Python Version

None

Screenshot

No response

Flow File

No response