[Bug]: Usage cost ignores Fast mode pricing

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

apps/server

Steps to reproduce

1. Enable Fast mode for a Codex or Claude provider session in T3 Code.
2. Run one or more turns that are served in Fast mode.
3. Open the Usage page.
4. Compare the displayed raw token cost with the provider’s Fast/Priority token rates.

Expected behavior

Fast mode should use the provider’s applicable Fast/Priority rates.
Standard responses should use standard rates, including when the provider falls back to standard processing.

Actual behavior

The Usage page prices all transcript usage at the base rate, so Fast mode price is under-reported

Impact

Cosmetic issue

Version or commit

main @ 5a8461480

Environment

All T3 Code server environments using Fast mode for Codex or Claude

Logs or stack traces

Screenshots, recordings, or supporting files

No response

Workaround

Ignore as inconsequential, or use the provider dashboard if the real number is important

Start in apps/server and trace how transcript usage is priced for the Usage page, focusing on Codex and Claude sessions and their Fast-mode metadata. Compare the provider’s Fast/Priority and standard rates, including fallback behavior. Done means Fast-mode usage uses the applicable rates while standard processing remains on standard pricing.