v0.21.0

[0.21.0] - 2026-06-03

Added

• Added experimental Antigravity IDE (Google DeepMind) as a fourth
  agent-runtime target (--runtime antigravity, combinable e.g.
  --runtime claude,antigravity). Renders GEMINI.md (project-level
  instruction file), shared .agents/skills/*/SKILL.md (same convention as
  Codex), and .agents/hooks.json with 6 hook groups mapped to Antigravity
  lifecycle triggers (PreInvocation, PreToolUse, PostToolUse, Stop).
  Guard enforcement works via AHK_RUNTIME=antigravity. Antigravity exposes
  ~5 of 9 Claude lifecycle triggers; UserPromptSubmit, PreCompact,
  SubagentStop, SessionEnd have no equivalent and are tracked as parity
  gaps. Vietnamese GEMINI.md template (--lang vi) is included from day
  one. doctor --runtime antigravity validates the GEMINI.md contract, hooks
  contract, and skill rendering. An E2E smoke (scripts/e2e-antigravity-cli.mjs)
  validates the generated surface including dual-runtime rendering. Use
  --runtime antigravity.

Documentation

• Updated README runtime support table and CLI examples with Antigravity.
• Updated docs/architecture.md with agent runtime rendering surface table.
• Updated schema/harness-spec.yaml consumer mapping cheat-sheet.

Validation

• node scripts/e2e-antigravity-cli.mjs: passed (7/7 checks).
• node --test tests/antigravity-adapter.test.mjs: passed (20/20 tests).
• npm test: 851 pass, 1 pre-existing fail (missing ajv dep), 2 skipped.

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Full history: CHANGELOG.md
Install: npx agent-harness-kit@0.21.0 init