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ToolResultFunctionMiddleware

NexusLabs.Foundry.MicrosoftAgentFramework.Workflows

NexusLabs.Foundry.MicrosoftAgentFramework.Workflows.Middleware

ToolResultFunctionMiddleware Class

MAF function-invocation middleware that intercepts [AgentFunction] return values and exceptions, ensuring the LLM always receives a structured JSON response instead of a raw stack trace.

public sealed class ToolResultFunctionMiddleware : NexusLabs.Foundry.MicrosoftAgentFramework.IAIAgentBuilderPlugin

Inheritance System.Object 🡒 ToolResultFunctionMiddleware

Implements NexusLabs.Foundry.MicrosoftAgentFramework.IAIAgentBuilderPlugin

Remarks

When an [AgentFunction] method returns a NexusLabs.Foundry.MicrosoftAgentFramework.Tools.IToolResult: - Success — the LLM receives the NexusLabs.Foundry.MicrosoftAgentFramework.Tools.IToolResult.BoxedValue directly. - Failure — the LLM receives { "error": { … } } (the NexusLabs.Foundry.MicrosoftAgentFramework.Tools.IToolResult.BoxedError wrapped), and the original System.Exception is preserved on NexusLabs.Foundry.MicrosoftAgentFramework.Tools.IToolResult.Exception for diagnostics.

When an [AgentFunction] throws an unhandled exception, the middleware catches it, wraps it in an NexusLabs.Foundry.MicrosoftAgentFramework.Tools.ToolResult.UnhandledFailure(System.Exception,System.Func{System.Exception,NexusLabs.Foundry.MicrosoftAgentFramework.Tools.ToolError}) result, and returns a safe generic error message to the LLM. NexusLabs.Foundry.MicrosoftAgentFramework.Tools.IToolResult.IsTransient is null in this case.

System.OperationCanceledException is intentionally not caught — it propagates so cooperative cancellation (parent timeouts, user cancels, structured-concurrency aborts) continues to function correctly. Tools that legitimately catch and translate cancellation should do so inside the tool body, not rely on this middleware.

Non-NexusLabs.Foundry.MicrosoftAgentFramework.Tools.IToolResult return values pass through unchanged.

Methods

ToolResultFunctionMiddleware.Configure(AIAgentBuilderPluginOptions) Method

Called once per agent creation to configure the builder's middleware pipeline. Use NexusLabs.Foundry.MicrosoftAgentFramework.AIAgentBuilderPluginOptions.AgentBuilder to add Use(...) middleware layers.

public void Configure(NexusLabs.Foundry.MicrosoftAgentFramework.AIAgentBuilderPluginOptions options);

Parameters

options NexusLabs.Foundry.MicrosoftAgentFramework.AIAgentBuilderPluginOptions

Provides access to the AIAgentBuilder for the agent being constructed.

Implements Configure(AIAgentBuilderPluginOptions)