Add comprehensive functionality review for untested TXTControl library

[Copilot]

Author requested code review of TXTControl (async Python library for fischertechnik TXT controller) without making edits, as hardware testing is unavailable.

Review Deliverable

Created FUNCTIONALITY_REVIEW.md with systematic analysis across 16 categories including architecture, protocol implementation, error handling, security, and performance.

Critical Bugs Identified

Three showstopper issues found through static analysis:

1. Line 173: Port hardcoded as 6500 instead of 65000 (contradicts README) - connection will fail
2. Line 302: Calls non-existent _Buffer.handle_data() - runtime AttributeError guaranteed
3. Line 683: Missing raise before TXTError() - silent failure on duplicate output slots

Key Findings

• Architecture: Well-designed asyncio patterns, proper resource management via context managers
• Protocol: Binary communication with struct packing, but no timeout/retry logic
• Validation: Pervasive lack of input validation (speeds, distances, PWM levels)
• Testing: Zero test coverage, author acknowledges untested status
• Documentation: Comprehensive README but contains port number discrepancy

Assessment

Library demonstrates strong async design and clean API improvement over ftrobopy, but is not production-ready. Requires critical bug fixes, input validation, and hardware validation before alpha release.

Review provides line-by-line issue tracking table, severity classifications, and prioritized remediation roadmap.

Original prompt

review the functionality as I can't text the program. do not edit the program

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