[Code Quality] Add antigravity engine to schema built-in engine catalog and reference docs

[github-actions]

Description

The antigravity engine is a first-class built-in engine used in production workflows (.github/workflows/smoke-antigravity.md) and listed in pkg/workflow/engine_definition.go, but it is completely absent from:

1. docs/src/content/docs/reference/engines.md — which lists only Copilot, Claude, Codex, Gemini, OpenCode, and Pi
2. pkg/parser/schemas/main_workflow_schema.json — engine ID/example descriptions omit antigravity

This means valid workflows using antigravity appear undocumented, and schema examples steer users away from a supported engine.

Suggested Changes

• Add antigravity to the engine list in docs/src/content/docs/reference/engines.md (line ~16-21)
• Add antigravity to the built-in engine ID descriptions/examples in pkg/parser/schemas/main_workflow_schema.json (around line ~12540-12550)
• Optionally add a brief description of the engine alongside its peers

Files Affected

• docs/src/content/docs/reference/engines.md
• pkg/parser/schemas/main_workflow_schema.json

Success Criteria

• antigravity appears alongside other built-in engines in the reference docs
• Schema examples/descriptions include antigravity as a valid built-in engine ID
• No regressions in schema validation or doc generation

Source

Extracted from Schema Consistency Check - 2026-07-20 #46731

Priority

Medium - Users authoring workflows with antigravity have no documentation guidance. Effort: ~1 hour.

🔍 Task mining by Discussion Task Miner - Code Quality Improvement Agent · 35.6 AIC · ⌖ 5.2 AIC · ⊞ 7K · ◷

• expires on Jul 21, 2026, 5:27 AM UTC-08:00

[github-actions]

This issue was automatically closed because it expired on 2026-07-21T13:27:11.563Z.

Closed by Workflow