AskUserQuestion auto-submits with empty response when called from custom commands/skills

Environment

• Claude Code version: 2.1.63
• OS: macOS (Darwin 25.2.0)
• Model: Opus 4.6 (Claude Max)
• Shell: zsh

Summary

AskUserQuestion tool calls auto-submit immediately with empty responses when invoked from within a custom command (via /command-name). The tool works correctly in normal conversation — it renders the interactive UI and blocks for user input. But when the same tool is called from a command, it returns instantly without displaying the question to the user.

Regression

This was working correctly on 2/27/2026. Broke on 2/28/2026. Same version (2.1.63), same machine, same files.

Minimal Reproduction

1. Create .claude/commands/test-ask.md:

---
description: Minimal AskUserQuestion test
allowed-tools: AskUserQuestion
---

Ask the user this question using AskUserQuestion:

Question: "Pick a color"
Header: "Color"
Options:
- "Red" — A warm color
- "Blue" — A cool color
- "Green" — A nature color

After the user answers, output: "You picked: [their answer]"

1. Start a fresh Claude Code session
2. Run /test-ask
3. Expected: Color picker UI renders, Claude waits for user to select an option
4. Actual: "User answered Claude's questions:" appears with an empty response, Claude immediately continues without waiting

Output

❯ /test-ask

⏺ User answered Claude's questions:
  ⎿  

⏺ It looks like the answer wasn't captured in the response. Could you tell me which
   color you picked — Red, Blue, or Green?

The user never sees the question or gets a chance to answer.

Working case (normal conversation)

In the same session, typing "Ask me to pick a color using AskUserQuestion" works correctly — the interactive UI renders and Claude waits for input.

What I've ruled out

| Hypothesis | Test | Result |
|---|---|---|
| Custom command content causing issue | Created brand-new minimal test-ask.md (above) with no dependencies | Bug reproduces with minimal command |
| Plugin interference | Disabled all custom plugins, retested | Bug persists |
| Project-specific issue | Reproduced across 4 different projects | Bug is global |
| Settings/permissions | Reviewed settings.json | No AskUserQuestion-related entries |

Impact

This breaks any command or skill that relies on AskUserQuestion for interactive user input. Commands that use multi-step discovery workflows (asking questions, collecting preferences, etc.) speed through all questions without collecting any user input.