[Code Quality] Add Antigravity engine to user-facing docs and schema built-in engine catalog

[github-actions]

Description

The Antigravity engine is implemented in pkg/workflow/antigravity_engine.go and used in production workflows (e.g. smoke-antigravity.md), but it is missing from:

1. The available-engine table in docs/src/content/docs/reference/engines.md
2. The built-in engine descriptions/examples in pkg/parser/schemas/main_workflow_schema.json

This creates a documentation gap where valid production configuration appears undocumented.

Suggested Changes

• Add Antigravity to the engine table in docs/src/content/docs/reference/engines.md
• Update pkg/parser/schemas/main_workflow_schema.json built-in engine descriptions/examples to include Antigravity alongside pi and other built-in engines
• Ensure the schema catalog matches the runtime registration in pkg/workflow/engine_definition.go

Files Affected

• docs/src/content/docs/reference/engines.md
• pkg/parser/schemas/main_workflow_schema.json
• pkg/workflow/engine_definition.go (reference only)
• pkg/workflow/antigravity_engine.go (reference only)

Success Criteria

• Antigravity engine appears in the available-engine table in engines.md
• Schema built-in engine descriptions include Antigravity
• make recompile passes without errors
• Schema consistency check no longer flags Antigravity as undocumented

Source

Extracted from [Schema Consistency] Schema consistency check - 2026-07-23

Priority

Medium — valid runtime feature is invisible to users consulting documentation

🔍 Task mining by Discussion Task Miner - Code Quality Improvement Agent · sonnet46 43 AIC · ⌖ 5.45 AIC · ⊞ 7.1K · ◷

• expires on Jul 23, 2026, 11:40 PM UTC-08:00

[github-actions]

This issue was automatically closed because it expired on 2026-07-24T07:40:20.754Z.

Closed by Workflow