## Why
The TUI computed proactive `Heads up, you have less than ...` warnings
before considering workspace credits. As a result, users could see
included-limit warnings even when they could continue using Codex with
workspace credits.
`has_credits` alone is not sufficient to determine whether finite
credits are usable: a spend-control hard limit can cap the reported
balance to zero while `has_credits` still reflects the workspace's raw
balance. Unlimited credits are the opposite case: they are usable even
though no numeric balance is reported.
## What changed
- suppress proactive TUI rate-limit usage warnings and the lower-cost
model nudge when usable workspace credits are available
- treat credits as usable when `has_credits` is true and either
`unlimited` is true or the parsed balance is positive
- continue showing warnings when the usable balance is zero, including
when a spend-control limit has capped otherwise available workspace
credits
- add regression coverage for zero-balance, positive-balance, and
unlimited workspace-credit snapshots
## Validation
- `just test -p codex-tui rate_limit_usage_warnings_`
Brooks
5013d10824