[Code Quality] Add antigravity engine to docs/src/content/docs/reference/engines.md #48800

Description

The antigravity engine is a fully supported built-in engine (see pkg/workflow/engine_definition.go and pkg/workflow/antigravity_installer.go) and is used in real workflows (.github/workflows/smoke-antigravity.md, engine.id: antigravity). However, the canonical engine reference doc omits it entirely.

Suggested Changes

• Add an antigravity entry to docs/src/content/docs/reference/engines.md alongside Copilot, Claude, Codex, Gemini, OpenCode, and Pi.
• Include install/setup notes consistent with pkg/workflow/antigravity_installer.go.
• Cross-check other engine-listing docs pages for the same omission.

Files Affected

• docs/src/content/docs/reference/engines.md
• (reference only, no code changes) pkg/workflow/engine_definition.go, pkg/workflow/antigravity_installer.go

Success Criteria

• antigravity appears in the engine reference doc with equivalent detail to other engines.
• No other engine docs pages are found to have the same gap (or follow-up issues filed if so).

Source

Extracted from Schema Consistency Check discussion #48781

Priority

Medium - user-facing documentation gap for a supported feature.

🔍 Task mining by Discussion Task Miner - Code Quality Improvement Agent · sonnet50 · 29.8 AIC · ⌖ 4.66 AIC · ⊞ 9.8K · ◷

• expires on Jul 29, 2026, 11:42 PM UTC-08:00