- Introduced `alpha-search` flag for Codex API keys to enable Alpha Search functionality. - Added `CredentialPolicyCodexAlphaSearchV1` for filtering and validating API keys compatible with Alpha Search. - Extended configuration, synthesizer, and watcher functionality to track and manage `alpha-search` flag changes. - Updated Codex executor to dynamically construct Alpha Search endpoint based on API key attributes. - Enhanced tests to validate Alpha Search flag handling, endpoint construction, and credential filtering. Closes: #4692