[BUG] Subagent cascade bug: Multiple parallel instances spawn on test failure

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

When a subagent creates a Python test script that encounters an error during execution, Claude Code spawns multiple parallel instances of the same subagent task instead of handling the failure gracefully.

Steps to Reproduce

1. Initiate a task that requires creating a test script
2. Have the subagent (in this case "flow-hawk") create a test file
3. When the test file encounters an error during execution
4. Observe multiple parallel instances of the same subagent task spawning

Actual Behavior

• Multiple "flow-hawk" instances executing "Implement adaptive window sizing" in parallel
• Redundant parallel execution of the same task
• Resource waste and potential conflicts from parallel writes

Evidence

<img width="507" height="799" alt="Image" src="https://github.com/user-attachments/assets/965f8cdc-3913-411f-83b0-f077c58b689f" />

Environment

• Claude Code version: 1.0.120
• OS: macOS Tahoe 26

• Context: Creating test_adaptive_integration.py (134 lines)

Impact

• Performance degradation
• Resource exhaustion
• Potential file conflicts from parallel writes
• Poor user experience requiring manual interruption (ctrl+t)

What Should Happen?

Expected Behavior

• Single subagent should handle test failure and retry/fix
• Error handling should be sequential, not parallel
• No duplicate subagent instances should spawn

Error Messages/Logs

Steps to Reproduce

1. Ask Claude Code to create a Python module with tests:

"Create an adaptive window sizing module with unit tests"

1. When it creates the test file, ensure it fails by asking:

"Make the test import a non-existent module"

1. Watch Claude Code attempt to run the failing test

1. Bug: Multiple parallel "flow-hawk" subagents spawn immediately (20+ instances all running "Implement adaptive window sizing")

Minimal trigger code:

# test_adaptive_integration.py
from non_existent_module import Something  # This import fails
def test_something():
    pass


Result: Cascade of parallel subagents instead of single error handling

### Claude Model

Opus

### Is this a regression?

Yes, this worked in a previous version

### Last Working Version

_No response_

### Claude Code Version

1.0.120

### Platform

Other

### Operating System

macOS

### Terminal/Shell

VS Code integrated terminal

### Additional Information

_No response_