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.NET: [Bug]: Exception in workflow, that is added as agent, results in json serialisation error message instead of exception #8012
Description
Description
Have a workflow that throws an exception. Have the workflow registered as an agent.
Call the agent. Instead of the actual exception being logged, it results in a JSON serialisation error towards the user.
This was an issue in Semantic Kernel already: microsoft/semantic-kernel#10708
Code Sample
var workflowAsAgent = builder
.AddWorkflow("super-agent", CreateWorkflowDelegate)
.AddAsAIAgent(); // Now the workflow can be used as an agentError Messages / Stack Traces
Internal (swallowed) exception:
Exception has occurred: CLR/System.InvalidOperationException
Exception thrown: 'System.InvalidOperationException' in Microsoft.Agents.AI.Workflows.dll: 'Executor 'AggregatorExecutor' cannot send messages of type 'MySolution.Workflow.RawAggregate'.'
at Microsoft.Agents.AI.Workflows.InProc.InProcessRunnerContext.<SendMessageAsync>d__30.MoveNext() in /home/vsts/work/1/s/agent-framework/dotnet/src/Microsoft.Agents.AI.Workflows/InProc/InProcessRunnerContext.cs:line 235What the user sees:
Serialization and deserialization of 'System.Reflection.MethodBase' instances is not supported. Path: $.TargetSite. (Code: execution_error)
Package Versions
<PackageVersion Include="Microsoft.Agents.AI" Version="1.20.0" />
<PackageVersion Include="Microsoft.Agents.AI.A2A" Version="1.20.0-preview.260831.1" />
<PackageVersion Include="Microsoft.Agents.AI.DevUI" Version="1.20.0-preview.260831.1" />
<PackageVersion Include="Microsoft.Agents.AI.Hosting.A2A" Version="1.20.0-preview.260831.1" />
<PackageVersion Include="Microsoft.Agents.AI.Hosting.A2A.AspNetCore" Version="1.20.0-preview.260831.1" />
<PackageVersion Include="Microsoft.Agents.AI.Hosting.AGUI.AspNetCore" Version="1.20.0-preview.260831.1" />
<PackageVersion Include="Microsoft.Agents.AI.Hosting.AspNetCore" Version="1.20.0-preview.260831.1" />
<PackageVersion Include="Microsoft.Agents.AI.Hosting.OpenAI" Version="1.20.0-alpha.260831.1" />
<PackageVersion Include="Microsoft.Agents.AI.Workflows" Version="1.20.0" />
<PackageVersion Include="Microsoft.Agents.AI.Workflows.Generators" Version="1.20.0" />.NET Version
.Net 10.0
Additional Context
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github-actions commentedon Sep 2, 2026
🤖 Automated triage reproduction notes (agent-authored — trust but verify)
Agent analysis
The bug is in dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowSession.cs::InvokeStageAsync at lines 538-552, where a WorkflowErrorEvent containing the original Exception is assigned to AgentResponseUpdate.RawRepresentation. It is triggered when a workflow-as-agent throws and a host serializes that raw representation. Minimal repro: run a throwing workflow through AsAIAgent(), select the emitted WorkflowErrorEvent raw representation, and serialize it with System.Text.Json.
dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowHostSmokeTests.cs1.20.0