- Updated session handling to replace `Session_id` and `Conversation_id` headers with new logic ensuring consistent use of `Cache.ID` and prompt keys.
- Restored `Session_id` as a priority extraction source for `ExtractSessionID`.
- Added tests to validate case-sensitive and case-insensitive headers, canonical account header usage, and session key preservation.
- Removed legacy support for deprecated `Conversation_id` header to clean up API.