[Bug] System tool tokens not included in current_usage input token count

Bug Description
It seems that current_usage's input tokens are not taking into consideration the tokens for system tools. My currently calculated statusline window is 162K. /context shows 181k window size and system tools are 19.8k. It's adding up for me.

<img width="1436" height="30" alt="Image" src="https://github.com/user-attachments/assets/61f84458-ed1e-47b8-828d-145b6f674a40" />

<img width="581" height="193" alt="Image" src="https://github.com/user-attachments/assets/06e9280b-bc2c-46e8-8aab-e2e3a721ab99" />

Wondering if the explanation is accurate or whether there is anything missing in it.
<img width="1381" height="400" alt="Image" src="https://github.com/user-attachments/assets/8f77aef7-a049-4272-a134-4496e8ddf220" />

Environment Info

• Platform: darwin
• Terminal: zed
• Version: 2.0.74
• Feedback ID: 8d8f2f23-5d68-4550-888e-e9609264cc69

Errors

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