All other search DTOs (SemanticSearchBodyDto, HybridSearchBodyDto, BrainQueryDto, BrainSearchDto) already enforce @MaxLength(500) on their query fields. SearchQueryDto.q was missed, leaving the full-text knowledge search endpoint accepting arbitrarily long queries. Adds @MaxLength(500) decorator and validation test coverage. Co-Authored-By: Claude Opus 4.6 <[email protected]>