[BUG] Plan agent doesn't call AskUserQuestion despite documentation and tool access

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?

## Description
Plan agent skips AskUserQuestion when requirements are ambiguous. Previous Plan Mode (main context)
consistently called this tool - desired behavior now missing.

## Current vs Expected

Current: Plan agent makes assumptions, returns plan without user input

Expected: Call AskUserQuestion for ambiguous choices (auth method, libraries, architecture),
then plan based on answers

## Evidence
ExitPlanMode docs mandate:
Before using this tool, ensure your plan is clear and unambiguous. If there are multiple valid
approaches or unclear requirements:

1. Use the AskUserQuestion tool to clarify with the user
2. Ask about specific implementation choices (e.g., architectural patterns, which library to use)

...

1. Only proceed with ExitPlanMode after resolving ambiguities

Plan agent has "All tools" access including AskUserQuestion.

## Reproduction

Input: "Plan authentication implementation"

Current behavior: Creates plan assuming specific auth method

Expected behavior:

1. AskUserQuestion with options: OAuth, JWT, sessions, third-party
2. User selects
3. Plan based on selection

What Should Happen?

Call AskUserQuestion for ambiguous choices (auth method, libraries, architecture),
then plan based on answers

Error Messages/Logs

Steps to Reproduce

Input: "Plan authentication implementation"

Current behavior: Creates plan assuming specific auth method

Expected behavior:

1. AskUserQuestion with options: OAuth, JWT, sessions, third-party
2. User selects
3. Plan based on selection

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.0.30

Platform

Anthropic API

Operating System

Other Linux

Terminal/Shell

Xterm

Additional Information

_No response_