NAT A2A & MCP per_user workflow not starting

Version

v1.8.0

Which installation method(s) does this occur on?

No response

Describe the bug.

Hi,

yesterday we wanted to start agentic workflows using Nemo Agent Toolkit v1.8 but it fails to start an workflow and raises an error for a specific combination of configurations. We believe it is a bug.

Our current setup:

We have an orchestrator agent workflow running and want to connect an sub-agent using A2A. The sub agent has a connect to an authenticated MCP server. As stated in the docs both, the orchestrator and the sub-agent are "per_user_react_agent" type and the MCP connect in the sub-agent is "per_user_mcp_client" and has an "mcp_oauth2" authentication method. However the sub-agent workflow fails to start with the following error:

[Paste the error here,2026-08-17 13:56:56 - ERROR - nat.cli.commands.start:243 - Failed to initialize workflow
Error: Must set a workflow before building

This is the whole traceback. We managed to narrow down the problem: The workflow launch fails when the sub-agent is "per_user_react_agent" and the mcp server is "per_user_mcp_client" type. When using the non per_user types the workflow starts but fails with an 401 Unauthorized for the MCP initialization, which is expected since we have an authenicated MCP server.

Are there problems with an A2A setup and per_user workflows in combination with MCP?

Please find attached our configs and startup commands. We are using Docker Containers as we are running in K8s. The images were built from the Dockerfile in the v1.8.0 tagged git release. The orchestrator is working as expected, only the sub-agent with the MCP connection raises the problems.

orchestrator_start_server.py
orchestrator_agent_config.yml

subagent_config.yml
subagent_start_server.py

We need your help to solve this.

Regards
Daniel

Minimum reproducible example

See attachments

Relevant log output

[Paste the error here,2026-08-17 13:56:56 - ERROR - nat.cli.commands.start:243 - Failed to initialize workflow
Error: Must set a workflow before building

Other/Misc.

No response

Code of Conduct

• I agree to follow the NeMo Agent Toolkit Code of Conduct
• I have searched the open bugs and have found no duplicates for this bug report

Start with nat.cli.commands.start at the reported failure and reproduce the configuration using the attached orchestrator_start_server.py, subagent_start_server.py, orchestrator_agent_config.yml, and subagent_config.yml. Compare startup behavior for per_user_react_agent with per_user_mcp_client and mcp_oauth2 against the non-per_user setup. Done means the A2A sub-agent workflow initializes without the “Must set a workflow before building” error while retaining authenticated MCP behavior.