test: cover Claude ultra no-op, Codex excludeUltra, mobile Priority

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Summary

Daily coverage pass for recently merged risky paths that lacked direct regression tests: Claude mid-session Codex ultra handling, Claude Codex-sub catalog excludeUltra, and the mobile home-composer Priority toggle synthesized from fast-only variants (#146).

Tiny testability extract only — mobile option synthesis moved into a pure helper; no user-facing behavior change.

Risky behavior now covered

• Claude mid-session ultra no-op — setModel with effort / reasoningEffort: 'ultra' must not call applyFlagSettings (Claude effortLevel has no ultra tier).
• Codex excludeUltra — defaultCodexReasoningEffortOption({ excludeUltra: true }) drops Multi-agent ultra from Claude Codex-sub picker rows (fix(server): drop Codex 'ultra' tier from Codex-sub rows in the Claude picker #143).
• Mobile Priority from variants — when a model only advertises fast via fast-only variants, the Options sheet synthesizes a Priority boolean toggle (fix(mobile): surface fast (Priority) toggle from model variants #146).

Test files added/updated

• apps/server/test/unit/agents/claude-agent.provider.spec.ts — ultra skip cases
• apps/server/test/unit/agents/codex-model-options.spec.ts — excludeUltra unit case
• apps/mobile/src/lib/model-option-descriptors.ts + .spec.ts — extracted helper + 5 specs
• apps/mobile/src/components/home-composer.tsx — uses the helper (behavior-preserving)

Why these tests materially reduce regression risk

• Sending invalid Claude effortLevel: 'ultra' mid-session can break live query flag updates for Codex-sub sessions.
• Re-adding ultra to Claude picker rows would offer a tier the Claude runtime cannot honor.
• Losing the Priority synthesis would hide a control users rely on for Codex/Cursor fast models on phone.

Changes

• Added regression specs for Claude ultra no-op and Codex excludeUltra
• Extracted composerModelOptionDescriptors for deterministic mobile coverage of fix(mobile): surface fast (Priority) toggle from model variants #146

Type

• test — test-only

Checklist

• TDD-first — wrote specs for the missing behaviors; mobile helper extracted to make them pass
• Suite is green — targeted: server Claude + Codex option specs (66 pass); mobile model-option-descriptors.spec.ts (5 pass)
• Changeset — skipped (<!-- no-changeset -->; test + behavior-preserving extract)
• Docs synced — N/A (no API/docs change)
• No secrets committed
• No new vulnerabilities introduced

Test plan

cd apps/server && bun test test/unit/agents/claude-agent.provider.spec.ts test/unit/agents/codex-model-options.spec.ts
cd apps/mobile && bun run test src/lib/model-option-descriptors.spec.ts

Related issues / PRs

Refs #143, #146. Follow-up to coverage automation #142.

Screenshots / recordings

N/A