[BUG] High baseline CPU/RAM on idle — v2.1.50 Windows 11

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?

Two separate Claude Code CLI instances in plain CMD consuming 29% CPU and 1.4 GB RAM combined while essentially idle. Fresh PC boot, vanilla setup — no MCP servers, no plugins, no custom CLAUDE.md. Both terminals are sluggish: input lag, slow scrolling, delayed response streaming. Rest of the system runs fine.

Instance 1: Reading old messages, no active task
Instance 2: Resumed session, ~49k/200k context tokens, no active task

| Process | CPU | RAM | Power Usage |
|---------|-----|-----|-------------|
| Claude Code #1 | 14.5% | 757 MB | Very High |
| Claude Code #2 | 14.5% | 636 MB | Very High |
| Chrome (10 tabs) | 1.2% | 634 MB | Low |

Environment:

• Version: 2.1.50
• OS: Windows 11
• Terminal: CMD
• Plan: Max5 subscription
• MCP servers: None
• Plugins: None
• No custom CLAUDE.md or rules

Related: #4953, #9711, #11122, #8968

Unlike those issues, this is not a gradual memory leak — it's high baseline consumption within minutes of a fresh boot on a completely vanilla setup.

What Should Happen?

A CLI tool should idle under 1-2% CPU, not 14.5% per instance. Memory should be in the 100-300 MB range, not 600-750 MB for a text-based terminal agent. Windows should not flag a command line tool as "Very High" power usage while it sits idle.

Error Messages/Logs

Steps to Reproduce

1. Fresh boot Windows 11 PC.
2. Open CMD, run claude. Read old messages — don't start any task.
3. Open second CMD, run claude, resume an older session (~49k tokens context).
4. Don't run any task in either instance.
5. Check Task Manager — observe 14.5% CPU, 600-750 MB RAM, and "Very High" power per process.

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.50

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

_No response_