Fixes 21 remaining open CodeQL alerts across 14 files: removed 1 unused import (response_limiter.py), added explanatory comments to 10 empty-except blocks (asyncio.CancelledError teardown patterns, optional imports, parse failures), and narrowed 10 broad BaseException/bare-except catches to specific types (ValueError, TypeError, AttributeError, JSONDecodeError, Exception). No behavioral changes - purely code quality fixes.