NexusFix

Use when building, reviewing, debugging, or optimizing NexusFIX-based C++ FIX protocol code. Covers session management, order entry, market data subscription, low-latency message parsing, and zero-allocation hot-path constraints. Also use when generating new FIX connectivity code that must follow C++23 best practices with std::expected error handling, fixed-point arithmetic, and SIMD-accelerated parsing.