Claude Code consumes 100%+ CPU when idle in terminal

Description

Claude Code (the CLI) consumes 100%+ CPU even when idle in a terminal session. This drains battery significantly on laptops.

Environment

• macOS 26.2 (Darwin 25.2.0)
• Claude Code installed via npm
• Running in terminal (both standalone and within tmux)

Reproduction

1. Start claude in a terminal
2. Leave it idle (not actively processing a request)
3. Observe CPU usage via ps aux | grep claude or Activity Monitor

Observed Behavior

$ ps aux | grep claude
user  52191 103.9  1.1 467673200 566032 s007  R+    8:04AM  34:21.11 claude 
user  48497  42.2  0.8 478110720 425616 s004  S+   Mon11AM  69:31.67 claude

Two Claude processes:

• One using 103.9% CPU (started today, running 34 min)
• One using 42.2% CPU (started Monday, running for days)

Stack Sample Analysis

Running sample <pid> shows the process is stuck in a tight loop:

737 uv__run_check  (in node) + 136  [0x104f9fc14]
  721 node::Environment::CheckImmediate(uv_check_s*)  (in node) + 400
    720 node::InternalMakeCallback(...)
      719 v8::Function::Call(...)
        [deep V8/JS execution]

This pattern suggests setImmediate() calls are being rapidly re-scheduled without proper yielding, causing a busy-wait loop instead of sleeping when idle.

Expected Behavior

When Claude Code is idle (waiting for user input), CPU usage should be near 0%.

Workaround

Kill the process: kill <pid>