[BUG] RangeError: Maximum call stack size exceeded during AskUserQuestion (post-parallel-agents)

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?

Environment

• Claude Code: v2.1.1
• Model: Opus 4.5
• Platform: macOS (Darwin, arm64/Homebrew)

Description

CLI crashed with stack overflow while displaying an AskUserQuestion prompt, after 3 parallel Explore agents had completed.

Reproduction

1. Run session with multiple file operations and commits
2. Launch 3 parallel Explore agents to investigate codebase
3. After agents complete, Claude triggers AskUserQuestion with multiple-choice options
4. While question UI is displayed (idle, waiting for input), crash occurs

Error

Exception in PromiseRejectCallback:
file:///opt/homebrew/lib/node_modules/@anthropic-ai/claude-code/cli.js:4549
[minified code dump]

RangeError: Maximum call stack size exceeded

Analysis

Visible code fragments show recursion in:

• Message normalization (query_message_normalization_start/end)
• I81 - recursive object traversal
• A70 - async generator wrapper
• API request preparation

This differs from #14860/#9157 (terminal rendering recursion) - the crash appears to be in conversation history processing, not text wrapping.

Possibly Related

• #14860 / #9157 - Stack overflow in terminal rendering
• #14897 - Parallel agents causing memory issues
• #8829 - Parallel agent crashes

Additional Context

• Crash occurred during idle state, not active processing
• Work completed before crash was preserved
• Session had accumulated context from 3 completed Explore agents

What Should Happen?

The AskUserQuestion prompt should remain stable while waiting for user input. The CLI should handle accumulated conversation context from completed parallel agents without stack overflow.

Error Messages/Logs

Exception in PromiseRejectCallback:
file:///opt/homebrew/lib/node_modules/@anthropic-ai/claude-code/cli.js:4549
[large minified code dump to stdout]

RangeError: Maximum call stack size exceeded

Exception in PromiseRejectCallback:
file:///opt/homebrew/lib/node_modules/@anthropic-ai/claude-code/cli.js:1562
[additional minified code dump]


The crash dumped significant chunks of minified internal JS to the terminal, including fragments related to prompt caching, message normalization, tool schema building, and recursive object traversal in function `I81`.

Steps to Reproduce

1. Start a Claude Code CLI session (v2.1.1, Opus 4.5)
2. Perform several operations to build up conversation context (file reads, bash commands, git commits)
3. Request a task that triggers 3 parallel Explore agents to investigate a codebase
4. Wait for all 3 agents to complete and return results
5. Claude triggers an AskUserQuestion with multiple-choice options
6. While the question UI is displayed and waiting for user input (idle state), crash occurs

Claude Model

Not sure / Multiple models

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.0.76

Claude Code Version

2.1.1

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Warp

Additional Information

_No response_