[Bug] Excessive CPU usage during idle state in parallel sessions

**Bug Description**
Claude code should not use cpu time idling. I run multiple claude code sessoin in parallel. every one consumes 3% cpu time doing nothin. they should consume no cpu time doing so.

**Environment Info**
- Platform: linux
- Terminal: tmux
- Version: 2.1.270
- Feedback ID: 588c9967-d669-47d3-b320-6f22d69aa176

Tasks: 520 total, 1 running, 519 sleeping, 0 stopped, 0 zombie
%Cpu(s): 2,2 us, 1,3 sy, 0,0 ni, 96,0 id, 0,4 wa, 0,0 hi, 0,0 si, 0,0 st
MiB Mem : 128518,6 total, 24585,8 free, 15944,7 used, 89864,3 buff/cache
MiB Swap: 30517,0 total, 30516,1 free, 0,9 used. 112573,8 avail Mem

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
521863 flo 20 0 1450,4g 264512 144284 S 7,4 0,2 0:02.91 chrome
1832323 root 20 0 28,6g 1,6g 466044 S 3,3 1,3 130:15.89 Xorg
3971231 flo 20 0 1161,7g 323108 111100 S 3,3 0,2 66:54.87 element-desktop
21599 flo 20 0 5582792 473976 120416 S 2,8 0,4 107:09.49 claude
1833334 flo 20 0 729256 75420 51724 S 2,8 0,1 11:17.60 xfce4-terminal
3278834 flo 20 0 5589912 368568 120532 S 2,8 0,3 32:00.54 claude
4088011 flo 20 0 53,0g 576544 312220 S 2,8 0,4 1:18.80 chrome
33462 flo 20 0 5586956 456864 120800 S 2,3 0,3 106:57.58 claude
3278476 flo 20 0 5594060 377732 120672 S 1,9 0,3 31:31.16 claude
3279219 flo 20 0 5589396 345988 120740 S 1,9 0,3 26:05.59 claude
3281622 flo 20 0 5591572 427844 120920 S 1,9 0,3 37:48.05 claude
526124 flo 20 0 1450,2g 109572 82720 S 1,4 0,1 0:00.15 chrome
4088054 flo 20 0 52,5g 147672 117176 S 1,4 0,1 0:45.09 chrome
1267 root 20 0 0 0 0 S 0,9 0,0 55:02.86 nvidia-modeset/kthread_q
4306 flo 20 0 463760 12772 9828 S 0,9 0,0 0:17.80 gvfs-udisks2-vo
518742 flo 20 0 5584556 278364 87952 S 0,9 0,2 0:11.59 claude
526088 flo 20 0 1450,2g 125424 96828 S 0,9 0,1 0:00.30 chrome
2706600 flo 20 0 5591616 309964 64380 S 0,9 0,2 9:23.12 claude
3281875 flo 20 0 5585252 322400 120396 S 0,9 0,2 25:30.21 claude

**Errors**
```json
[]
```

Start by reproducing the idle behavior with multiple Claude Code sessions in Linux under tmux, using the reported version and process monitor output as a baseline. Trace which idle activity accounts for the CPU time. Done means idle sessions no longer consume measurable CPU, while active sessions continue to work normally.

Written by the indexing model from the issue text.