- Add `is-compat` support to OpenAI compatibility model config, capabilities, hashing, and example config.
- Propagate `IsCompat` through API-key model resolution and switch OpenAI-compat executor translation to compatibility-aware routing.
- Keep Claude assistant thinking content in compatibility mode while keeping default behavior unchanged when `is-compat` is disabled.
Closes: #4776
- Added `is-compat` model metadata plumbing from config through executor and helpers, including hash computation.
- Introduced a compatibility-aware translation path (`TranslateRequestWithAPIKeyModelCompatibility`) and wired it into Claude/Gemini/Codex/Interactions request flows.
- Updated Claude message sanitization/translation behavior to keep empty-thinking compatibility blocks (including signatures) when `is-compat` is enabled, while keeping default behavior unchanged.
