[AT-230]: Add follow_up_refinement agent event type

[dmitrycnstrc]

The agent now emits a follow_up_refinement SSE event (a narrowing question with
selectable options). The Agent module only subscribes to event types listed in
Agent.EventTypes, so the event was silently dropped from the stream.

[Copilot]

🟡 Changes recommended

The newly added test introduces inconsistent string quoting that likely violates existing style/lint conventions in the spec file.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Adds support for a new Agent SSE event type (follow_up_refinement) so it is no longer dropped by the stream listener, and updates typings/tests to match.

Changes:

• Added FOLLOW_UP_REFINEMENT to Agent.EventTypes so the listener subscribes to it.
• Extended TypeScript declarations with AgentEventTypes and FollowUpRefinementEventData.
• Added a unit test asserting follow_up_refinement events are enqueued into the stream.

File summaries

File	Description
src/types/agent.d.ts	Adds typings for Agent.EventTypes and the new refinement event payload shape.
src/modules/agent.js	Registers follow_up_refinement in the static EventTypes map so it’s listened for.
spec/src/modules/agent.js	Adds coverage ensuring the new event type is enqueued into the readable stream.

Review details

• Files reviewed: 2/3 changed files
• Comments generated: 1
• Review effort level: Lite

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[Copilot]

🟢 Approval recommended

The change is small, consistent across runtime + typings, and includes a focused test verifying the new event type is forwarded.

Review details

• Files reviewed: 2/3 changed files
• Comments generated: 0 new
• Review effort level: Lite