Debugging MDC Context Loss in Java 21 Virtual Threads: Why ThreadLocal Fails Under Load

Java 21's virtual threads promise dramatic throughput improvements for high-concurrency systems, but they expose fatal flaws in ThreadLocal-based context handling like Logback's MDC. Context loss and memory leaks become inevitable under virtual thread scheduling. This demands a migration to Java 21's Scoped Values for thread-safe, leak-free distributed tracing in production.