/usage should work while command code is actively working

Summary

/usage cannot be checked while command code is actively running a task. This makes it hard to monitor usage during long-running tasks, which is when usage information is most useful.

Expected Behavior

i should be able to run /usage while command code is working and see the usage that has already been recorded.

the currently in-flight request does not need to be included. it could simply show usage through the last completed request.

Actual Behavior

while command code is actively working, i cannot use /usage to check my current usage. i have to wait until the task/turn finishes before i can see it.

for long-running tasks this means i cannot tell how much of my usage limit has already been consumed while deciding whether to let the task continue or interrupt it.

Steps to reproduce the issue

1. start command code
2. give it a task that takes a while to complete
3. while command code is still actively working, try to run /usage
4. /usage does not immediately show the current recorded usage
5. wait for the active task to finish
6. /usage can then be checked normally

Command Code Version

1.26.0

Operating System

macOS

Terminal/IDE

ghostty

Shell

zsh

Session file (optional)

No response

Fix prompt (optional)

No response

Additional context

OS: macOS Tahoe 26.6.1

从 /usage 命令的入口点开始，跟踪活动任务运行期间使用量的记录方式。使用一个长时间运行的任务重现该问题，然后验证 /usage 会报告截至最后一个已完成请求的使用量，而无需等待任务完成。