[BUG] Second account shows 100% usage after first prompt despite zero prior usage — same billing method as another account

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?

When switching Claude Code to a second, previously-unused account (via
/login → "Claude account with subscription") that shares the same credit
card as another account I use, the very first prompt sent on the new account
immediately results in 100% usage shown on claude.ai — despite this account
never having been used before.

This has happened 3 times over 3 consecutive days, always right after
switching accounts.

This appears to be the same root cause as #41881 ("Accounts on the same
billing method share a single rate limit quota pool"), where usage quota
is pooled server-side by billing method rather than tracked independently
per account.

What Should Happen?

Each account should have its own independently tracked usage quota,
regardless of shared billing method, since each is sold and billed as a
separate $20/month subscription.

Error Messages/Logs

Steps to Reproduce

1. Have two separate Claude accounts (different organizations), both on

paid subscriptions, using the same credit card

1. Exhaust session usage on Account 1 in Claude Code
2. Run /login in Claude Code, select "Claude account with subscription",

authenticate as Account 2 (which has zero prior usage)

1. Send a single prompt on Account 2
2. Check usage on claude.ai for Account 2 — it immediately shows 100% used,

even though this is the very first prompt ever sent on this account

Note: I have not yet confirmed whether usage is already at 100% immediately
upon login before sending any prompt — only that it reaches 100% right after
the first prompt.

Claude Model

_No response_

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.251

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

Other

Additional Information

This is a regression — I have been switching between these two accounts
regularly for all time without this issue occurring.
The problem started 1 or 2 weeks ago and has now happened 3 times, always
right after switching accounts.