[KingUdo]

Summary of Changes

• Introduced MAX_CONCURRENT_CLIENTS (default: 100, configurable via environment variable).
• Enforced a concurrency limit in start_telnet_server using threading.BoundedSemaphore.
• If the maximum connection limit is reached, incoming connections are rejected immediately with a friendly message (Server busy. Connection closed.) and closed, preventing unbounded thread spawning and memory/OS resource exhaustion.
• Ensured the semaphore is released in the finally block of handle_client.
• Added unit test test_handle_client_releases_semaphore to verify resource cleanup.
• Fixes Denial of Service risk: Unbounded thread spawning on client connections #3.

Testing

Ran pytest across the whole suite:

============================== 19 passed in 3.17s ==============================