Chore/include action metadata from API responses

[HenryHengZJ]

Issue

When an agentflow hits a human-in-the-loop node (human input or agent tool approval), an action object is created containing approve/reject buttons and context data. This action is stored in the database and streamed via SSE to the UI — but it is not returned in the non-streaming prediction API response for agentflows. Developers building on the prediction API cannot detect when human input is needed without parsing SSE streams.

Fix

Add action to agentflow non-streaming response

[gemini-code-assist]

Code Review

This pull request introduces the handling of an 'action' field across several server-side components, including event publishers and flow builders, to ensure consistent metadata propagation. A review comment suggests an optimization in 'buildAgentflow.ts' to use an existing object directly instead of performing a redundant JSON parse.