[Node] Add onElicitationRequest Callback for Elicitation Provider Support

[MRayermannMSFT]

REQUIRES CHANGES FROM TO BE RELEASED: https://github.com/github/copilot-agent-runtime/pull/5267

What

Adds onElicitationRequest to the Node.js SDK's SessionConfig, enabling SDK clients to act as elicitation providers — receiving and responding to form-based UI dialog requests from the agent runtime. The SDK automatically negotiates the requestElicitation capability during session create/resume, handles elicitation.request RPC callbacks, and keeps session.capabilities up to date via capabilities.changed events as providers join or leave. Includes E2E tests covering capability reporting, multi-client capability propagation, and provider disconnect cleanup, along with updated README documentation.

Why

The CLI runtime now supports fan-out elicitation — dispatching structured input requests to all connected clients that advertise elicitation support, with the first response winning. Without this SDK-side change, Node.js clients had no way to register as elicitation providers, meaning these requests could only be served by the CLI's own TUI.

[github-actions]

Cross-SDK Consistency Review

This PR adds onElicitationRequest callback support to the Node.js/TypeScript SDK, enabling clients to act as elicitation providers. While this is a valuable feature addition, it creates a feature parity gap across the SDK implementations.

Summary of Changes (Node.js Only)

The PR adds:

1. onElicitationRequest handler in SessionConfig and ResumeSessionConfig
2. ElicitationHandler and ElicitationRequest types
3. requestElicitation flag sent during session create/resume
4. RPC handler registration for elicitation.request callbacks
5. Automatic capabilities.changed event handling to update session.capabilities dynamically
6. Comprehensive documentation in README with examples
7. E2E tests covering single-client and multi-client scenarios

Feature Parity Status

SDK	OnUserInputRequest	OnElicitationRequest	capabilities.changed handling
Node.js	✅ Supported	✅ Added in this PR	✅ Added in this PR
Python	✅ Supported	❌ Missing	❌ Missing
Go	✅ Supported	❌ Missing	❌ Missing
.NET	✅ Supported	❌ Missing	❌ Missing

Recommendation

The Python, Go, and .NET SDKs should receive equivalent implementations to maintain feature parity. Based on the Node.js changes, each SDK would need:

Python (python/copilot/)

• Add on_elicitation_request: ElicitationHandler to SessionConfig and ResumeSessionConfig (similar to on_user_input_request)
• Define ElicitationHandler type alias following the existing UserInputHandler pattern
• Add request_elicitation flag to create/resume RPC calls
• Register RPC handler for elicitation.request in client.py
• Implement _register_elicitation_handler() method in CopilotSession
• Handle capabilities.changed events to update session.capabilities dynamically
• Add README documentation and E2E tests

Go (go/)

• Add OnElicitationRequest ElicitationHandler to SessionConfig and ResumeSessionConfig
• Define ElicitationHandler func(request ElicitationRequest, invocation ElicitationInvocation) (ElicitationResponse, error)
• Add RequestElicitation bool to create/resume RPC params
• Register RPC method handler for elicitation.request in client.go
• Implement registerElicitationHandler() and handleElicitationRequest() in session.go
• Handle capabilities.changed events in session event processing
• Add README documentation and E2E tests

.NET (dotnet/src/)

• Add OnElicitationRequest property to SessionConfig and ResumeSessionConfig
• Define ElicitationHandler delegate following the UserInputHandler pattern
• Add RequestElicitation to create/resume RPC parameters
• Register RPC handler for elicitation.request in Client.cs
• Implement RegisterElicitationHandler() and handle callbacks in Session.cs
• Handle capabilities.changed events to update session capabilities
• Add README documentation and E2E tests

Note on Blocking

This should not block the Node.js PR from merging, but I recommend:

1. Creating follow-up issues/PRs to track implementation in other SDKs
2. Documenting this as a Node.js-only feature temporarily in the main README
3. Prioritizing Python/Go/.NET implementations to minimize the feature gap duration

The implementation pattern is consistent and well-tested in Node.js, making it straightforward to port to the other SDKs following their respective language idioms.

Generated by SDK Consistency Review Agent for issue #908 · ◷