[deep-report] Document antigravity engine in engines.md and fix stale built-in engine comments

[github-actions]

Description

The schema-consistency audit (#44217, 2026-07-08) found the antigravity engine ships and is used in real workflows (pkg/workflow/antigravity_engine.go, pkg/workflow/data/engines/antigravity.md, .github/workflows/smoke-antigravity.md) but is invisible in docs/comments:

• docs/src/content/docs/reference/engines.md supported-engine catalog omits antigravity.
• pkg/workflow/engine_definition.go top comment and the NewEngineCatalog comment still list built-ins as only claude, codex, copilot, gemini, opencode, crush — omitting both pi and antigravity.

Add antigravity (and pi) to the engines.md catalog/examples and update the stale engine_definition.go comments to match the actual catalog.

Expected Impact

Users reading docs/comments get the correct supported-engine set; reduces confusion and mis-authoring. Also relevant to the recurring "Smoke Antigravity produced no safe outputs" failures.

Suggested Agent

Docs / Schema Consistency agent.

Estimated Effort

Fast (< 30 min)

Data Source

DeepReport 2026-07-08 · schema-consistency report #44217

Generated by 🔬 Deep Report · 301.4 AIC · ⌖ 10.9 AIC · ⊞ 10K · ◷

• expires on Jul 10, 2026, 7:37 AM UTC-08:00

[github-actions]

🍪 Issue Monster selected this for Copilot

I've identified this issue as a good candidate for automated resolution and requested assignment to the Copilot coding agent.

If assignment succeeds, the Copilot coding agent will analyze the issue and create a pull request with the fix.

Om nom nom! 🍪

🍪 Om nom nom by Issue Monster · 1.25 AIC · ⌖ 6.22 AIC · ⊞ 7.9K · ◷