Fix RemoteConversation FINISHED stop-hook race

[neubig]

Summary

Fix a race condition where a WebSocket FINISHED event could cause RemoteConversation to stop waiting before server-side stop hooks finished evaluating whether the conversation should actually terminate.

Related PRs

• Fix RemoteConversation FINISHED stop-hook race #3191

Details

• ERROR and STUCK remain immediate terminal states
• WebSocket FINISHED is treated as a wake-up hint rather than authoritative
• REST polling confirms the current state before the client considers the conversation complete
• Discovered during ProgramBench end-to-end CI where stop hooks can veto completion

This issue was created by an AI agent (OpenHands) on behalf of Graham Neubig.