Billing bug: Extra usage pool consumed while session limit still has remaining capacity

Description

Extra usage pool is being consumed even though included session usage still has remaining capacity (showing 95%). The expected behavior is that included plan usage is exhausted first before extra usage is billed.

Steps to Reproduce

1. Using Claude Code with Opus 4.6 (1M context) model
2. Working in a session with normal usage
3. Checked usage dashboard: session limit shows ~95% remaining, but extra usage pool is fully depleted
4. Claude Opus[1m] stops with API Usage Rate Limits

Expected Behavior

Included session/plan usage should be consumed first. Extra usage pool should only be drawn from after included usage is fully exhausted.

Actual Behavior

Extra usage pool was consumed (and depleted) while session limit still showed ~95% remaining capacity. This resulted in unexpected charges.

Environment

• Model: Claude Opus 4.6 (1M context) — claude-opus-4-6[1m]
• Platform: Linux (WSL2)
• Date observed: 2026-02-28

Impact

Unexpected financial charges from extra usage pool being consumed prematurely. Requesting investigation and refund/credit for incorrectly billed extra usage.

So nearly the entire included session allocation was untouched, yet the extra usage pool was fully depleted. This means almost all usage was incorrectly billed to the extra usage pool instead of the included plan allocation.