.NET: Make anonymous AG-UI session persistence safe in AGUIServer sample

[rogerbarreto]

Problem

The AGUIClientServer/AGUIServer sample enables WithInMemorySessionStore() but does not register an AgentIsolationKeyProvider. Anonymous POST requests therefore fail before the model call because strict session isolation cannot produce a key.

Simply setting withIsolation: false is not a safe general solution. The endpoint accepts caller-provided thread and run identifiers, and the singleton in-memory store would allow anonymous callers who know those identifiers to access the same retained conversation state.

Desired behavior

The local sample should support anonymous multi-turn conversations without sharing server-retained state between unrelated clients.

Possible approaches include:

• Generate a high-entropy client-scoped key and send it through a header or cookie consumed by an AgentIsolationKeyProvider.
• Keep the server stateless and have the client resend complete conversation history.
• Add a purpose-built anonymous isolation helper with clear local-development limits.

Acceptance criteria

• The documented REST/client flow works without an authenticated principal.
• Separate anonymous clients cannot resume each other's conversations using only thread or run identifiers.
• The sample explains how production deployments should use authenticated principal claims.
• Retained anonymous sessions have an explicit cleanup or bounded-lifetime strategy.

[hey-Chloe]

Hi, I’d like to work on this issue. I reviewed the isolation failure and the follow-up discussion in #7986, including why withIsolation: false was reverted.

I propose taking the stateless path described here: remove server-side session storage from the anonymous AGUIServer sample, have AGUIClient resend the complete conversation history, and document that production persistence must be isolated by a stable authenticated principal. This avoids treating caller-controlled thread/run IDs as an identity boundary and avoids retaining unbounded anonymous state.

I’ll add provider-free TestServer regression coverage for two-turn anonymous conversations and verify that reusing thread/run IDs cannot expose another client’s server-retained state. I’ll also run the relevant .NET build and AG-UI integration tests.

If this direction matches the maintainers’ intent, please assign #7993 to me.