#23250: feat: add Sonnet 4.6 forward compat for google-antigravity

## Summary Google Cloud Code Assist (google-antigravity) already serves `claude-sonnet-4-6` and `claude-sonnet-4-6-thinking` — the Antigravity IDE exposes them — but pi-ai's `models.generated.js` has not been updated to include these entries yet. This means configuring `google-antigravity/claude-sonnet-4-6-thinking` in openclaw fails with "Unknown model". This PR adds `resolveAntigravitySonnet46ForwardCompatModel`, mirroring the existing `resolveAntigravityOpus46ForwardCompatModel` pattern. It clones the registered `claude-sonnet-4-5-thinking` / `claude-sonnet-4-5` templates with the 4.6 model IDs so users can use Sonnet 4.6 on antigravity without waiting for a pi-ai catalog update. ### What changed - Added `ANTIGRAVITY_SONNET_46_*` constants (model IDs, template IDs) following the existing Opus 4.6 pattern - Added `resolveAntigravitySonnet46ForwardCompatModel` function handling both thinking and non-thinking variants, with dash and dot model ID formats - Wired it into the `resolveForwardCompatModel` chain ### Why forward compat instead of a models.generated.js update The model registry is generated from pi-ai's catalog. Until that catalog is updated, forward compat is the standard pattern used by openclaw for new model variants (see Opus 4.6, GPT 5.3 Codex, GLM-5, Anthropic Sonnet 4.6 on native provider). ## Test plan - [ ] Configure `google-antigravity/claude-sonnet-4-6-thinking` as primary or fallback model - [ ] Verify model resolves without "Unknown model" error - [ ] Verify API calls succeed against Google Cloud Code Assist endpoint 🤖 Generated with [Claude Code](https://claude.com/claude-code) <!-- greptile_comment --> <h3>Greptile Summary</h3> This PR adds forward compatibility support for Claude Sonnet 4.6 models on the `google-antigravity` provider, mirroring the existing Opus 4.6 pattern. The implementation correctly handles both dash (`claude-sonnet-4-6`) and dot (`claude-sonnet-4.6`) model ID formats, as well as thinking and non-thinking variants. **Key changes:** - Added Sonnet 4.6 model ID constants and template fallbacks - Implemented `resolveAntigravitySonnet46ForwardCompatModel` following the Opus pattern - Wired the resolver into the forward-compat chain **Issue found:** - Missing `ANTIGRAVITY_SONNET_46_FORWARD_COMPAT_CANDIDATES` export that's needed for `openclaw models list` to show these models (see inline comment) The core resolution logic is solid and matches the established pattern. Once the export is added and `list.registry.ts` is updated to consume it, Sonnet 4.6 will work seamlessly. <h3>Confidence Score: 3/5</h3> - Safe to merge after addressing the missing export for model listing - The implementation correctly follows the established Opus 4.6 pattern and the resolution logic will work. However, the missing `ANTIGRAVITY_SONNET_46_FORWARD_COMPAT_CANDIDATES` export means these models won't appear in `openclaw models list` output, which is a discrepancy with how Opus 4.6 works and likely unintended. - `src/agents/model-forward-compat.ts` needs the export added, and `src/commands/models/list.registry.ts` should be updated to consume it _{Last reviewed commit: 95b7319} <!-- greptile_other_comments_section --> <!-- /greptile_comment -->