commit_message.txt

🏗️ Architect: Centralize Study Key Validation

🏗️ Design Change:
Simplified `KeepStudyKeyStrategy` and `PopStudyKeyStrategy` by moving the logic that raises `ClientError` for a missing study key fully to `EndpointABC._validate_study_key()`, rather than keeping duplicate exception handling in the strategies.

♻️ DRY Gains:
Eliminated duplicate validation code; removed `exception_cls` argument dependency, ensuring all study key presence validations are centralized exactly in one place without dual execution.

🛡️ Solidity:
Reduced logical complexity inside strategies which are now purely responsible for property extraction / state mutation, strictly adhering to Single Responsibility Principle.

⚠️ Breaking Changes:
None. The validation is identical but now occurs consistently in `EndpointABC._validate_study_key()`.