#16687: fix(antigravity): default to Gemini 3 Pro and remove broken deprecated model defaults

## Summary Describe the problem and fix in 2–5 bullets: - Problem: Antigravity Claude defaults (`...claude-opus-4-5-thinking` and earlier `...4-6-thinking`) are currently unreliable in practice. - Why it matters: New users land on a broken default model path immediately after auth, causing first-run failures. - What changed: Set Antigravity default model to `google-antigravity/gemini-3-pro-high`; updated testing docs/examples to use Gemini Antigravity models instead of Claude Antigravity defaults. - What did NOT change (scope boundary): No OAuth protocol logic, no token storage format, no provider ID changes. ## Change Type (select all) - [x] Bug fix - [ ] Feature - [ ] Refactor - [x] Docs - [ ] Security hardening - [ ] Chore/infra ## Scope (select all touched areas) - [ ] Gateway / orchestration - [ ] Skills / tool execution - [x] Auth / tokens - [ ] Memory / storage - [x] Integrations - [ ] API / contracts - [ ] UI / DX - [ ] CI/CD / infra ## Linked Issue/PR - Closes # - Related #14203 ## User-visible / Behavior Changes List user-visible changes (including defaults/config). If none, write `None`. - New Antigravity auth setups now default to `google-antigravity/gemini-3-pro-high`. - Live testing docs/examples now emphasize Gemini Antigravity models. ## Security Impact (required) - New permissions/capabilities? (`Yes/No`) No - Secrets/tokens handling changed? (`Yes/No`) No - New/changed network calls? (`Yes/No`) No - Command/tool execution surface changed? (`Yes/No`) No - Data access scope changed? (`Yes/No`) No - If any `Yes`, explain risk + mitigation: ## Repro + Verification ### Environment - OS: macOS - Runtime/container: Node 22 + pnpm workspace - Model/provider: google-antigravity - Integration/channel (if any): onboarding auth default + docs - Relevant config (redacted): N/A ### Steps 1. Run Antigravity auth setup flow. 2. Inspect generated default model in config/profile result. 3. Check docs live-testing examples for Antigravity model references. ### Expected - Default points to `google-antigravity/gemini-3-pro-high`. - Docs no longer recommend Antigravity Claude defaults. ### Actual - Matches expected in changed files. ## Evidence Attach at least one: - [ ] Failing test/log before + passing after - [x] Trace/log snippets - [ ] Screenshot/recording - [ ] Perf numbers (if relevant) Scoped checks executed during commit helper: - `oxlint --type-aware --fix docs/help/testing.md extensions/google-antigravity-auth/index.ts` - `oxfmt --write --no-error-on-unmatched-pattern docs/help/testing.md extensions/google-antigravity-auth/index.ts` ## Human Verification (required) What you personally verified (not just CI), and how: - Verified scenarios: Confirmed default model constant and docs examples now target Gemini Antigravity model IDs. - Edge cases checked: Ensured examples still include at least two Antigravity models (`gemini-3-pro-high`, `gemini-3-flash`) for smoke runs. - What you did **not** verify: Full live auth + streaming execution against Google Antigravity. ## Compatibility / Migration - Backward compatible? (`Yes/No`) Yes - Config/env changes? (`Yes/No`) No - Migration needed? (`Yes/No`) No - If yes, exact upgrade steps: ## Failure Recovery (if this breaks) - How to disable/revert this change quickly: Revert commit `45b192c15`. - Files/config to restore: `extensions/google-antigravity-auth/index.ts`, `docs/help/testing.md`. - Known bad symptoms reviewers should watch for: New setups still defaulting to Antigravity Claude models. ## Risks and Mitigations List only real risks for this PR. Add/remove entries as needed. If none, write `None`. - Risk: Some users may prefer previous Claude default behavior. - Mitigation: Users can still manually set any supported model; this only changes the default path. ## AI Assistance - [x] AI-assisted - [x] Lightly tested Agent-Signoff: LobsterGuard <!-- greptile_comment --> <h3>Greptile Summary</h3> Changes default Antigravity model from broken `google-antigravity/claude-opus-4-6-thinking` to working `google-antigravity/gemini-3-pro-high` and updates test examples throughout documentation. - Updated `DEFAULT_MODEL` constant in `extensions/google-antigravity-auth/index.ts:20` - Modified `isModernModelRef` filter in `src/agents/live-model-filter.ts:63` to only accept Gemini models for antigravity provider - Added test coverage in `src/agents/live-model-filter.test.ts` to verify Gemini-only filtering - Updated documentation examples in `docs/help/testing.md` to reference working Gemini models The Chinese translation docs (`docs/zh-CN/help/testing.md`) still contain old model references, but per AGENTS.md lines 33-34, Chinese docs are auto-generated and should be updated via the translation pipeline rather than manually. <h3>Confidence Score: 4/5</h3> - Safe to merge with minimal risk - straightforward default model change with appropriate test coverage - Changes are well-scoped to fixing broken defaults. Test coverage added for the filter logic change. Documentation updated consistently. The only minor gap is the Chinese docs not being updated, but per repository guidelines these are auto-generated and shouldn't be manually edited. The PR correctly preserves backward compatibility logic in `model-forward-compat.ts` for users who may still reference the old Claude models. - No files require special attention _{Last reviewed commit: c12ad9d} <!-- greptile_other_comments_section --> <!-- /greptile_comment -->