- Introduce `CleanJSONSchemaForAntigravityClaudeTool` and model-aware schema sanitization helpers to flatten multi-branch `anyOf`/`oneOf` unions specifically for Antigravity Claude tool parameter schemas.
- Preserve multi-branch union support for Gemini model variants while preventing Claude backend HTTP 400 validation errors on nested unions.
- Ensure proper inheritance of nullable markers and idempotency across the translator and executor chain.
Closes: #3662