[Code Quality] Add missing engine to schema built-in engine catalog and remove deprecated alias examples

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Description

The schema consistency check found two gaps: (1) a runtime-supported engine is missing from the built-in engine catalog in docs/ and the schema, causing false validation expectations; (2) deprecated underscore-form alias examples still appear in documentation despite the parser treating them as deprecated.

Suggested Changes

• Add the missing engine name to the built-in engine catalog in the schema file
• Add the engine to the top-level frontmatter docs overview table
• Remove or update deprecated copilot_engine underscore alias examples in documentation
• Ensure the schema and docs match actual runtime support

Files Affected

• Schema file (built-in engine catalog section)
• Frontmatter documentation overview
• Any doc files still showing deprecated copilot_engine alias

Success Criteria

• Schema engine list matches runtime-supported engines
• Deprecated alias examples removed from docs
• make recompile and docs validation pass

Source

Extracted from Schema Consistency Check - 2026-07-16 #45924

Priority

Medium — prevents user confusion from schema/docs lagging behind runtime

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• expires on Jul 18, 2026, 5:23 PM UTC-08:00

[github-actions]

This issue was automatically closed because it expired on 2026-07-19T01:23:59.503Z.

Closed by Workflow