[WIP] Add regression coverage for model propagation in workflow

[Copilot]

Thanks for asking me to work on this. I will get started on it and keep this PR's description up to date as I form a plan and make progress.

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This section details on the original issue you should resolve

<issue_title>[squad-plan] Add regression coverage for model propagation from workflow frontmatter to aw_info and engine runtime</issue_title>
<issue_description>## Objective
Add focused tests that lock in correct propagation of top-level workflow model through compilation artifacts and runtime configuration.

Issue context

Issue #50312 exposed a likely gap in test coverage: Avenger specified model: claude-haiku-4.5, but audited runs used claude-opus-4-8. Even once the underlying bug is fixed, we need durable regression coverage around model propagation to prevent recurrence.

Implementation guidance

• Add targeted tests near existing engine/aw_info coverage in pkg/workflow.
• Cover at least:
  • top-level model on a Claude engine workflow
  • activation job outputs exposing the same model
  • generated aw_info step receiving the expected model value
  • runtime engine config/args not silently swapping to a different default
• If useful, add a narrow audit-side test only if reporting logic contributed to the mismatch.

Acceptance criteria

• New tests clearly cover top-level model propagation for the Claude engine path.
• Tests would catch a future regression where frontmatter says one model but activation/runtime uses another.
• Test additions are targeted and pass with existing workflow/unit test runners (make test-unit).

Dependency / ordering notes

Best done immediately after or alongside the model-mismatch fix issue. If that investigation reveals the problem is only in reporting (not runtime), tailor these tests to the true failure point.

Generated by 🧑‍🤝‍🧑 Squad Plan · auto · 37.1 AIC · ⌖ 2.24 AIC · ⊞ 9.5K · ◷
_{Comment /squad-plan to run again}

• Closes [squad-plan] Add regression coverage for model propagation from workflow frontmatter to aw_info and engine runtime #50318

Comments on the Issue (you are @copilot in this section)

• Fixes [squad-plan] Add regression coverage for model propagation from workflow frontmatter to aw_info and engine runtime #50318