[BUG] AskUserQuestion silently returns empty results without rendering UI

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

AskUserQuestion tool calls return immediately with empty answers without ever rendering the selection UI to the user. The model then proceeds by hallucinating the user's choices from context.

⏺ User answered Claude's questions:
⎿

This happened 17+ consecutive times in a single session, and reproduced across two separate sessions (different session IDs, fresh launches). The model hallucinated plausible answers each time and proceeded as if the user had made real selections.

What Should Happen?

AskUserQuestion should render its selection UI (options with labels, descriptions, multi-select support) and wait for the user to make a choice before returning.

Error Messages/Logs

Steps to Reproduce

1. Install Claude Code v2.1.63
2. Run any workflow that calls AskUserQuestion multiple times (e.g., an interactive skill/workflow with multi-step question flows)
3. Observe that the transcript shows User answered Claude's questions: with empty results for every call
4. The model interprets empty answers as valid responses and continues

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.1.62

Claude Code Version

2.1.63

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

• v2.1.63 was installed Feb 28 15:59; bug observed in sessions starting Feb 28 16:53+
• Binary size jumped from 187MB (v2.1.62) to 192MB (v2.1.63), suggesting substantial changes
• No hooks, plugins, or settings explain the behavior — PostToolUse hook is a benign context monitor, SessionStart hook is a background update checker
• Global permissions allow: Read, Edit, Write, WebFetch, Bash — AskUserQuestion is not listed
• Session was using /gsd:discuss-phase