[agent-issue]: Mirror gh-aw's runtime model controls in ado-aw #2245

Submission requirements

• I generated this issue with an agent that used .github/agents/ado-aw.agent.md.
• I reviewed the generated issue and confirm it is being filed directly in githubnext/ado-aw.

Problem summary

Allow operators to switch the main agent and threat-detection models through Azure DevOps pipeline variables or variable groups, mirroring gh-aw's runtime model controls.

During a model outage, changing hardcoded models currently requires editing workflow markdown, regenerating the lockfile, and merging a PR. Runtime controls would let subsequent runs use an available model without that turnaround.

Reproduction details

Inspected ado-aw v0.52.1 and main at c1ae381:

• engine.model: "$(REVIEW_MODEL)" is rejected by model-identifier validation.
• engine.env.COPILOT_MODEL: "$(REVIEW_MODEL)" is rejected because only specific provider environment keys allow ADO expressions.

These are source-confirmed restrictions, not an executed standalone repro. This is a feature request, not a hosted-run failure.

Proposed next step

Mirror gh-aw's precedence using proposed ADO variables:

1. Explicit model configured for the engine instance.
2. ADO_AW_MODEL_AGENT_COPILOT or ADO_AW_MODEL_DETECTION_COPILOT.
3. Shared ADO_AW_DEFAULT_MODEL_COPILOT.
4. Existing default behavior.

Resolve variables at pipeline runtime, preserve existing explicit-model behavior, and record the effective models in run metadata. Pass values through environment mappings with validation and quoted arguments rather than direct shell substitution. Cover precedence, missing/invalid values, and independent detection selection with tests.

Posted by Copilot CLI assistant.