test(codex): repair dev by granting the gated 5.6 roster to candidate-scope preview cases

[lidge-jun]

Summary

dev is currently red. #2515 and #2550 were each green in isolation, but their
interaction is semantic: #2550 made gpt-5.6-* account-gated and fails closed when the
entitlement snapshot carries no roster for an account (src/codex/auth-context.ts:463),
while two account-preview cases added by #2515 bind on gpt-5.6-sol without installing a
roster mock. On dev both now throw CodexPoolAuthenticationError: No eligible Codex account supports this model.

This grants those two cases the same roster the neighbouring preview cases already install
(installCodexRosterMock with GPT56_NATIVE_MODELS, the pattern introduced by #2550
itself at lines 732 and 793). Test-only change; no runtime behaviour is modified.

Failing run before the fix: https://github.com/lidge-jun/opencodex/actions/runs/32863008724

Verification

$ bun test tests/subagent-model-fallback.test.ts tests/subagent-fallback-handle-responses.test.ts
 88 pass
 0 fail
 238 expect() calls

Before the change the same command reported 86 pass / 2 fail.

Checklist

• Targets dev
• Focused regression run locally
• No runtime behaviour change (test fixture only)
• No secrets or account details in the diff

Summary by CodeRabbit

• Tests
  • Updated subagent fallback pool tests to reflect account eligibility for gated models.
  • Improved test coverage for affinity binding and entitlement handling.

[github-actions]

✅ Deterministic PR hygiene checks passed.

[coderabbitai]

Caution

Review failed

The pull request is closed.

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: 7c9ddead-8b46-4016-b0b5-fb27eaec9004

📥 Commits

Reviewing files that changed from the base of the PR and between e42778a and 3a5b81e.

📒 Files selected for processing (1)

• tests/subagent-fallback-handle-responses.test.ts

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📝 Walkthrough

Walkthrough

Two subagent fallback tests now install Codex roster mocks that grant GPT56_NATIVE_MODELS to both pool accounts. This keeps account-gated bindings eligible during affinity setup. No production code changed.

Changes

Fallback test entitlement setup

Layer / File(s)	Summary
Install roster mocks before fallback binding tests/subagent-fallback-handle-responses.test.ts	The fallback preview and recovery preview tests grant GPT56_NATIVE_MODELS to pool_acc_a and pool_acc_b before binding affinity. This prevents the account-gated gpt-5.6-sol binding from failing closed with no eligible account. Lines 846–851 and 919–923.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Suggested reviewers: ingwannu

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch codex/fix-subagent-fallback-entitlement-roster

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