[BUG] Claude Code Terminal Hang After Pasting Text

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?

Claude Code completely hangs when pasting text into the terminal. After pasting ~31 lines, the terminal became unresponsive - couldn't type, Ctrl+C and Ctrl+Q didn't work. Had to kill -9 the process.

Debugging revealed the process had written 162 MB to stdout (from pasting 31 lines) and was blocked in a write() system call. The terminal showed bracketed paste mode indicator [201~[Pasted text #1 +31 lines] and "INSERT" mode before freezing.

claude_hang_lsof.txt
claude_hang_trace.txt
mcp_playwright_lsof.txt
mcp_playwright_trace.txt

What Should Happen?

Pasting text should not generate massive output or hang the terminal. Even with large output, Claude Code should:

• Handle terminal backpressure gracefully
• Buffer or paginate output appropriately
• Remain interruptible with Ctrl+C
• Not block indefinitely on write operations

claude_hang_lsof.txt

Error Messages/Logs

No error messages - terminal completely froze. Before hang, terminal showed:

[201~[Pasted text #1 +31 lines]
-- INSERT -- ⏵⏵ accept edits on (shift+tab to cycle)

Then became completely unresponsive.

Steps to Reproduce

1. Start Claude Code in a project directory
2. Paste approximately 30+ lines of text into the terminal
3. Terminal shows bracketed paste mode: [201~[Pasted text #1 +31 lines]
4. Terminal shows "INSERT" mode message
5. Terminal hangs completely

Note: Could not reproduce consistently - only happened once. May be timing or content-dependent.

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.0.37 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

iTerm2

Additional Information

What I was doing:
Working in my project directory

[201~[Pasted text #1 +31 lines]
-- INSERT -- ⏵⏵ accept edits on (shift+tab to cycle)

Then it froze completely.

What I Found

I used sample and lsof to debug the hung process before killing it:

Process was blocked writing to terminal:

PID    %CPU  STATE  TIME
93814  0.0   S+     3:51.79

0% CPU means it wasn't spinning - it was blocked on I/O.

Stack trace showed it was stuck in write():

8646/8842 samples (98%) in:
  kevent → waiting for I/O
  
176/8842 samples (2%) in:
  node::StreamBase::Write → write (in libsystem_kernel.dylib)

The process was blocked trying to write to the terminal.

File descriptor showed massive output:

node 93814  1u  CHR  16,9  0xa251366  895  /dev/ttys009

That offset 0xa251366 = 170,000,102 bytes = ~162 MB of data written to stdout.

The Issue

When I pasted ~31 lines of text, Claude Code somehow generated 162 MB of output trying to process or display it, which completely overwhelmed the terminal buffer. The write operation blocked indefinitely, and the entire terminal became unresponsive.

Debug Data Collected

I captured full traces before killing the process:

Process info:

• PID: 93814
• Working directory: /Users/sandman/Documents/project
• Started: Nov 12 20:41:38
• Hung at: Nov 13 20:27:47 (had been running fine for ~24 hours until paste)

Stack trace: Full sample output showing 98% of time in kevent (waiting) and 2% blocked in write()

Open files: lsof showing 170 MB written to terminal device

MCP servers active:

• mcp-server-playwright (PID 44833) - trace shows it was idle during hang

Can provide full sample traces and lsof output files if needed for investigation.

Terminal Configuration

• Terminal: iTerm2
• Shell: zsh with oh-my-zsh
• Bracketed paste mode: Active (evidenced by [201~ escape sequence)

Why Ctrl+C Didn't Work

The process was blocked in a kernel system call (write), so it couldn't process signals until the write completed. Since the terminal couldn't consume 162 MB of data, the write never completed, creating a deadlock.