[Code Quality] Add antigravity engine to schema examples and engines.md documentation

[github-actions]

Description

The antigravity engine is registered as a built-in in pkg/workflow/engine_definition.go and used in .github/workflows/smoke-antigravity.md, but it is absent from the JSON schema engine examples and missing from docs/src/content/docs/reference/engines.md. Users writing workflows cannot discover it from the docs or get schema completion for it.

Suggested Changes

1. Add antigravity to the engine enum/examples in pkg/parser/schemas/main_workflow_schema.json (currently only copilot and claude are shown).
2. Add an antigravity section to docs/src/content/docs/reference/engines.md with configuration examples.
3. Update docs/src/content/docs/reference/frontmatter.md to add a short engine.extensions subsection alongside the existing engine.driver entry.
4. Remove or demote the deprecated safe-outputs.dispatch_repository alias from docs/src/content/docs/reference/frontmatter-full.md — replace with a migration note pointing to the canonical spelling.

Files Affected

• pkg/parser/schemas/main_workflow_schema.json — expand engine examples
• docs/src/content/docs/reference/engines.md — add antigravity section
• docs/src/content/docs/reference/frontmatter.md — add engine.extensions subsection
• docs/src/content/docs/reference/frontmatter-full.md — demote deprecated alias

Success Criteria

• Schema provides antigravity as a valid engine option with description
• engines.md documents antigravity with a usage example
• frontmatter.md covers engine.extensions
• Deprecated alias is marked clearly and not shown as a primary example

Source

Extracted from Schema Consistency Check 2026-07-21 #46991

Priority

Medium — documentation gap causes user confusion; engine is fully functional but undiscoverable

🔍 Task mining by Discussion Task Miner - Code Quality Improvement Agent · 39.1 AIC · ⌖ 5.29 AIC · ⊞ 7K · ◷

• expires on Jul 21, 2026, 11:40 PM UTC-08:00

[github-actions]

This issue was automatically closed because it expired on 2026-07-22T07:40:03.638Z.

Closed by Workflow