[BUG] Claude Code Stopping mid-execution using Haiku 4.5

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?

Use Case: Our use case here is driving iOS e2e tests on CI, running claude code in a headless prompt mode, integrating with mobile-mcp and taking screenshots of the active simulator, etc.
These premature exits are happening maybe in 50% of tests, with some tests needing 3-4 auto-resumes.

Issue occurs when abort signal check happens after empty assistantMessages check, causing premature exit instead of proper abort handling.

Key findings:

Abort signal checked too late (line 649 vs line 555 in query.ts)
APIUserAbortError returns without yielding messages
No validation for unexpectedly empty assistantMessages array
Includes reproduction scenario, code locations, and potential solutions.

Logs
Pre-execution stop - claude_output_1.json
Post-execution stop - claude_output_2.json

What Should Happen?

Claude should not stop execution
claude_output_1.json

claude_output_2.json

Error Messages/Logs

See attached Logs

Steps to Reproduce

Claude Model

Haiku 4.5

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.0.30

Platform

Anthropic API

Operating System

Other

Terminal/Shell

Other

Additional Information

_No response_