Set explicit supported Copilot model for GitHub Guard Coverage Checker

[Copilot]

The scheduled GitHub Guard Coverage Checker (MCP + CLI) workflow was failing in the agent step due to an unsupported model configuration (400 The requested model is not supported). This change pins the workflow to a supported Copilot model to prevent non-transient model-selection failures.

• Workflow frontmatter update

  • Converted engine config from scalar to explicit object in .github/workflows/github-mcp-guard-coverage-checker.md.
  • Pinned model to gpt-5.4 for deterministic model selection.

• Compiled lock alignment

  • Updated .github/workflows/github-mcp-guard-coverage-checker.lock.yml to match the source workflow change:
    • GH_AW_INFO_MODEL: gpt-5.4
    • COPILOT_MODEL: gpt-5.4
    • refreshed frontmatter_hash metadata to stay in sync with the .md workflow.

Example of the effective source change:

engine:
  id: copilot
  model: gpt-5.4

[Copilot]

✅ Ready to approve

The change is narrowly scoped to workflow configuration, is internally consistent across source + lock, and directly addresses the reported non-transient model-selection failure.

Note: this review does not count toward required approvals for merging.

Pull request overview

This PR fixes the scheduled GitHub Guard Coverage Checker (MCP + CLI) workflow’s agent step failing due to unsupported/invalid model selection by pinning the workflow to a known supported Copilot model.

Changes:

• Updated the workflow frontmatter to use an explicit engine object and set model: gpt-5.4.
• Updated the compiled lock workflow to align with the frontmatter change, including setting GH_AW_INFO_MODEL and COPILOT_MODEL to gpt-5.4 and refreshing the frontmatter_hash.

File summaries

File	Description
.github/workflows/github-mcp-guard-coverage-checker.md	Switches engine from scalar to object and pins the Copilot model to gpt-5.4 in source frontmatter.
.github/workflows/github-mcp-guard-coverage-checker.lock.yml	Aligns the compiled workflow with the pinned model by setting runtime env vars to gpt-5.4 and updating metadata hashes.

Copilot's findings

• Files reviewed: 2/2 changed files
• Comments generated: 0

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