[BUG] Background subagents silently auto-deny permissions (Write tool)

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?

When running subagents in background mode, permission requests for tool use are silently auto-denied without user prompts. Subagents report successful completion but operations never execute.
This appears to be a broader issue affecting multiple tool types in background mode (related to #30693 which affects Bash permissions).

Current behavior:

• Subagents silently auto-deny Write permissions across all scenarios
• Return success status despite operations failing
• No user notification or error messages
• Main agents detects failed tool usage after it read all subagent outputs

What Should Happen?

• Permissions should be inherited from parent session, OR
• User should be prompted for permission (forwarded to foreground), OR
• Background subagents should fail with clear error messages indicating permission denial

Error Messages/Logs

No error provided

Steps to Reproduce

1. Create multiple subagents to generate and write files
2. Run them in parallel using background task execution
3. Monitor subagent execution - reports show success
4. Verify files exist on disk - they don't

Occurs in multiple scenarios:

• Subagents with no tool allows provided (general purpose)
• Subagents with tool allows explicitly configured (custom subagents)
• Subagents initially run in foreground, allowed tool use and then moved to background afterwards
• Subagents created with run_in_background: true from start

Claude Model

Not sure / Multiple models

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

Claude Code ( 2.1.71)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

_No response_