fix(codex): stop inferring Fast tier from model or reasoning effort

[swear01]

Bug

The Codex StatusBar can still show a green fast badge when Fast service tier is not active.

After #904 added real serviceTier plumbing, StatusBar.tsx retained a heuristic fallback: low/minimal/none reasoning effort, or a model name containing mini/fast, is treated as Fast mode. Codex CLI /fast is a distinct catalog-provided service tier, not a reasoning level or model size.

Expected behavior

• Show the Codex fast badge only when the explicit session/service tier says Fast is active.
• Do not infer Fast from reasoning effort or model name.
• Add tests covering unset tier + low effort, unset tier + mini model, explicit Fast, and Standard/off.

Regression/incomplete follow-up to #904; related acceptance criteria were originally tracked in #898.

[github-actions]

Confirmed. The current web status bar can still show the green fast badge even when serviceTier is unset, because it falls back to model/reasoning heuristics. Specifically, unset tier + none/minimal/low reasoning, or a model string containing mini/fast, currently evaluates as Fast mode.

The explicit service-tier plumbing does exist elsewhere (fast / standard), so this looks localized to the StatusBar display fallback and missing render tests for the badge cases you listed.

Relevant code:

• web/src/components/AssistantChat/StatusBar.tsx:133 - isCodexFastMode() infers Fast from reasoning effort and model name.
• web/src/components/AssistantChat/StatusBar.tsx:218 - status bar uses explicit serviceTier when present, but falls back to the heuristic when it is null/undefined.
• web/src/components/AssistantChat/StatusBar.tsx:265 - green fast badge renders when codexFastMode is true.
• web/src/components/AssistantChat/HappyComposer.tsx:1258 - serviceTier is passed into StatusBar.
• shared/src/apiTypes.ts:150 - service-tier API schema treats Fast mode as explicit fast / standard values.
• hub/src/web/routes/sessions.ts:597 - /service-tier applies the explicit session config.
• cli/src/codex/utils/appServerConfig.ts:65 - stored service tier maps fast to Codex app-server priority, standard to null, and unset to omitted.
• web/src/components/AssistantChat/StatusBar.test.ts:4 - current StatusBar test coverage only checks whether the bar is shown for agent flavors; no fast-badge render cases found.

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HAPI Bot