[BUG] High CPU usage (5-10%) during idle and file operations on Windows

Describe the bug
Claude Code consumes 5-10% CPU even when idle, with spikes during file edit operations on Windows.

To Reproduce

1. Launch Claude Code CLI on Windows
2. Observe CPU usage while Claude is idle (no active prompts)
3. CPU usage sits at 5%
4. During file edit operations (Edit tool), CPU spikes to 10%

Expected behavior
CPU usage should be minimal (< 1%) when idle and during simple file operations.

Environment

• OS: Windows
• Claude Code version: Latest
• Context: Working with multiple git repositories in additional working directories

Additional context
This is noticeably impacting system performance during extended sessions. There's a related issue #17359 about usage increases on launch, but this persists throughout the entire session even when no work is being done.

Impact
High CPU usage makes it difficult to keep Claude Code running during long work sessions, especially on resource-constrained systems.