Ring Buffer Bug: Modulus Empty Check Silently Drops Full Payloads

A subtle logic flaw in a C++ ring buffer implementation caused the empty() function to incorrectly return true after the buffer was completely filled. The bug stemmed from using modulus-based equality to compare read and write pointers, which produces identical residues when the buffer is exactly full or genuinely empty. Because the error involved no undefined behavior, tools like UBSan and ASan raised no alerts, and all existing unit tests continued to pass. The only observable symptom was silently dropped payloads downstream, making the defect easy to overlook during code review. The fix replaces the modulus check with a simple subtraction of raw cursor values to accurately track occupancy, distinguishing full from empty states reliably.