[codex] suppress low usage remaining warnings when credits are available

[brooks-oai]

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_

[chatgpt-codex-connector]

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