AG-UI .NET — troubleshooting

Goal: map a symptom to its cause and fix in an AG-UI .NET app.

The agent forgets earlier turns / history is truncated

The server is stateless and keeps nothing between turns, so the client must resend the full history each turn. If you send only the latest message, the model loses all prior context.

Fix: keep a running List<ChatMessage>, append the assistant reply (history.AddMessages(updates.ToChatResponse())), and resend the whole list. For a server that holds the conversation, keep the thread id stable by reusing the same ChatOptions instance across turns.

update.ConversationId is always null

This is by design — the SDK never surfaces a service conversation id. A non-null ConversationId would make Microsoft.Extensions.AI wrappers send only deltas, which truncates history against a stateless server.

Fix: don't track conversations by ConversationId. Use the thread id from the RUN_STARTED event (update.RawRepresentation as RunStartedEvent), or just reuse the same ChatOptions to keep one stable thread.

State, reasoning, or lifecycle updates never arrive

These ride on content-less updates — update.RawRepresentation (a StateSnapshotEvent, RunStartedEvent, RawEvent, …) with no text. The non-streaming GetResponseAsync aggregation drops updates that carry no message content.

Fix: consume the streaming API (await foreach over GetStreamingResponseAsync) and inspect update.RawRepresentation / update.Contents inside the loop, rather than aggregating to a single ChatResponse.

A tool throws at runtime or emits AOT/trim warnings

A tool whose argument or result type is non-primitive needs source-generated serialization; reflection-based schema/binding fails under Native AOT and trimming.

Fix: put the tool's parameter and result types in a JsonSerializerContext, register it on the host (ConfigureHttpJsonOptions(o => o.SerializerOptions.TypeInfoResolverChain.Add(...))), and pass it to AIFunctionFactory.Create(method, serializerOptions: ctx.Options).

An unknown-tool call errors mid-run

When the client declares a tool the server doesn't own, the server's function-invoking client tries to execute it and fails — unless told the call belongs elsewhere.

Fix: register the server chat client with .UseFunctionInvocation(fic => fic.TerminateOnUnknownCalls = true). The unknown (client) tool then ends the server turn cleanly and is forwarded to the client to execute.

The endpoint returns 406 Not Acceptable

Transport is content-negotiated. A 406 means the request's Accept header asked for a format the server can't produce (e.g. protobuf with no protobuf formatter registered, or an Accept that excludes text/event-stream).

Fix: make the client accept a format the server offers. For SSE, allow text/event-stream (or */*); for protobuf, register ProtobufEventStreamFormatter on the server and list it in the client's AGUIEventStreamHandler.

An interrupt or approval won't resume

Resuming a paused run needs both the request and the matching response in the resumed message list, sharing the same id — the SDK pairs them to reconnect to the paused call.

Fix: append both — the ToolApprovalRequestContent (or InterruptRequestContent) on an assistant message and its CreateResponse(...) / InterruptResponseContent(requestId) on a user message — then stream again. Sending the response alone leaves nothing to resume.

Inspecting what's on the wire

See the raw event frames directly with curl:

curl -N -X POST http://localhost:5000/ \
  -H "Content-Type: application/json" -H "Accept: text/event-stream" \
  -d '{"threadId":"t1","runId":"r1","messages":[{"id":"m1","role":"user","content":"Hi"}]}'

A healthy run shows RUN_STARTED … TEXT_MESSAGE_CONTENT … RUN_FINISHED. A paused run ends RUN_FINISHED { outcome: interrupt }. Tool runs show TOOL_CALL_START / TOOL_CALL_ARGS / TOOL_CALL_END / TOOL_CALL_RESULT.

In code, telemetry and custom server events surface as a RawEvent on the update:

if (update.RawRepresentation is RawEvent { Source: var source, Event: var payload })
{
    Console.WriteLine($"[{source}] {payload.GetRawText()}");
}

Verify the fix

After applying a fix, reproduce the original prompt and confirm the symptom is gone against the wire stream — e.g. the second turn now reflects the first (history), the StateSnapshotEvent now arrives (streaming), or the response Content-Type now matches the negotiated transport (406).