[Question] Recommended way to pass server-side userId when using AG-UI starter with HarnessAgent?

[likebean]

Context

We are building a multi-user platform with:

• Backend: Spring Boot + Spring Security (session/cookie auth)
• Agent: HarnessAgent (singleton, stateless engine with AgentStateStore)
• Frontend: CopilotKit → AG-UI protocol
• Integration: agentscope-agui-spring-boot-starter (AguiRestController / AguiAgentAdapter)

Per the Context & AgentState docs, (userId, sessionId) should be passed via RuntimeContext on each call. The Quickstart also shows userId / sessionId being set in the HTTP handler.

However, the AG-UI integration path seems different from the HarnessGateway / builder example (ChatController → MsgContext.userId → RuntimeContext).

What we observed

1. RC4 (AguiAgentAdapter): calls agent.stream(msgs, options) without RuntimeContext, so threadId is not mapped to sessionId.
2. main (after fix(agui): propagate run input and frontend tools #1895): buildRuntimeContext() sets sessionId = threadId and puts RunAgentInput into context — but still no userId.
3. Without userId, ReActAgent falls back to __anon__/{sessionId} slot keys, which breaks multi-user isolation when multiple logged-in users share the same AG-UI threadId namespace.

We understand userId should come from the integration layer (server auth), not from the frontend forwardedProps (untrusted).

Questions

1. Is there an official recommended pattern for passing server-side authenticated userId into RuntimeContext when using the AG-UI Spring Boot starter with HarnessAgent?
2. Should we wait for / contribute to the hook mechanism proposed in Feature Request: Support Custom Agent Hooks via forwardedProps #901 (AguiRequestHook + forwardedProps), or is there a better extension point (e.g. custom AguiRequestProcessor, RuntimeContextCustomizer)?
3. For production multi-tenant chat, do you recommend staying on AG-UI + starter, or switching to the builder-style HarnessGateway path (custom SSE, not AG-UI)?

Related issues / PRs

• [Feature]: Agui mode does not expose sessionId during agent execution, preventing saveTo / session persistence #751 — AG-UI sessionId not exposed during execution (persistence)
• Feature Request: Support Custom Agent Hooks via forwardedProps #901 — Custom hooks via forwardedProps (open)
• fix(agui): propagate run input and frontend tools #1895 / fix(agui,harness): propagate runtime context and harden shell working_directory #1780 — RuntimeContext propagation for AG-UI (sessionId ← threadId)

Our current workaround

Wrapping the registered Agent to inject SecurityContext → RuntimeContext.userId before delegating to HarnessAgent.stream(..., ctx). This works but feels like integration-layer logic placed at the wrong abstraction level.

Any guidance or planned API for this scenario would be appreciated. Happy to contribute a PR if there is a preferred design.

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Environment: agentscope-java 2.0.0-RC4, Spring Boot 3.4, Java 17