Subagent UI spam: Agent output printed repeatedly in terminal

Description

I'm experiencing a UI issue where subagent output gets printed 10s to hundreds of times in the terminal while the agent is working. The repeated output makes it appear as if the agent might be caught in a loop, though I can't confirm this is actually happening.

<img width="569" height="906" alt="Image" src="https://github.com/user-attachments/assets/1a498c8a-d65f-4f5f-a2fe-5045060bded3" />

Expected Behavior

Subagent output should be displayed once or with reasonable frequency updates.

Actual Behavior

The same subagent output gets printed repeatedly (10s to 100s of times) in the terminal, creating spam-like behavior.

Impact

• Makes it difficult to follow actual progress
• Terminal becomes cluttered with repeated messages
• Unclear if agent is actually looping or just UI display issue

Environment

• Platform: macOS (Darwin 23.5.0)
• Using Claude Code CLI

Steps to Reproduce

Occurs intermittently when using subagents for various tasks - no specific reproduction steps identified yet. But seems to be potentially occuring when implementing code against test cases, but can't cofirm this is what is causing it. It could also be caused by a long running session against a masterfully well crafted implementation plan 😉